{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_37682/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_37682","id":"gutenberg_37682","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/37682","summary":null,"tags":["Category: Philosophy & Ethics","Category: Science - Chemistry/Biochemistry","Category: Teaching & Education","Chemistry -- Early works to 1800"],"text":"Produced by Bryan Ness, LN Yaddanapudi and the Online\nDistributed Proofreading Team at https://www.pgdp.net (This\nbook was produced from scanned images of public domain\nmaterial from the Google Print project.)\n\n\n\n\n\n    [Transcriber's Note: A few typographical errors have been\n    corrected. Details are given at the end of the text.]\n\n\n\n\nHEADS OF LECTURES\n\nON A COURSE OF\n\nEXPERIMENTAL PHILOSOPHY,\n\nPARTICULARLY INCLUDING\n\nCHEMISTRY,\n\nDELIVERED AT THE NEW COLLEGE\nIN HACKNEY.\n\n_By JOSEPH PRIESTLEY, LL.D. F.R.S._\n\nAC. IMP. PETROP. R. PARIS. HOLM. TAURIN. AUREL. MED.\nPARIS. HARLEM. CANTAB. AMERIC. ET PHILAD. SOC.\n\nQUI DOCET DISCIT.--WM. LILLY\n\nLONDON:\n\nPRINTED FOR J. JOHNSON, NO. 72, ST. PAUL'S CHURCH-YARD.\n\n1794.\n\n\n\n\nTHE PREFACE.\n\n\nSituated, as I happily am, in the neighbourhood of the _New College at\nHackney_, an institution that does honour to the Dissenters, an\ninstitution open to all persons without distinction[1], and connected as\nI am by friendship with the tutors, I was glad to give it every\nassistance in my power; and therefore undertook to read the _Lectures on\nHistory and General Policy_ which I had composed when I was tutor at\nWarrington, and also to give another course on the subject of\n_Experimental Philosophy_. With this view I drew up the following _Heads\nof Lectures_; and, to save the students the trouble of transcribing\nthem, they are now printed. To other persons they may serve as a\ncompendious view of the most important discoveries relating to the\nsubject.\n\n    [Footnote 1: One gentleman of the Roman Catholic persuasion, and\n    several of the Church of England, are now in the College.]\n\nAs it was found most convenient, with respect to the other business of\nthe college, to confine this course to one lecture in a week, I\ncontrived to bring within that compass as much of the subject of\nexperimental philosophy as I well could, and especially to include the\nwhole of what is called _chemistry_, to which so much attention is now\ngiven, and which presents so many new fields of philosophical\ninvestigation.\n\nBesides that the plan of the young gentlemen's studies would not admit\nof it, I think it most advisable not to trouble beginners with more than\na large outline of any branch of science. By this means they are not\nfatigued by too long an attention to any one subject, a greater variety\nof articles may be brought before them, and in future life they may\npursue any of them as much farther as their inclination may dispose, and\ntheir ability and opportunity shall enable, them to do it.\n\nI do not give any account of the _experiments_ introduced into the\nseveral lectures. They will be sufficiently indicated by the subjects of\nthem. They were as many as I could conveniently make within the time;\nand where the experiments themselves could not be made, I usually\nexhibited both the different substances employed in them, and those that\nwere the result of them.\n\nAs these lectures were calculated for the use of the students at the New\nCollege, I prefix an _Address to them_, the same in substance with that\nwhich I delivered to them at the close of the session of 1791. In it may\nbe seen a specimen of the language we hold to them on the subject of\n_politics_, which with reasonable men will serve as an answer to the\nmany calumnies that have been thrown out against us, as disaffected to\nthe government of this country.\n\nSuch institutions will, indeed, always be objects of hatred and dread to\n_bigots_ and the advocates for _arbitrary power_, but the pride of a\ntruly _free country_. I therefore conclude with my earnest prayer (the\naccomplishment of which the present state of the College does not allow\nus to doubt) ESTO PERPETUA.\n\n\n\n\nTHE DEDICATION.\n\nTO THE STUDENTS AT THE NEW COLLEGE IN HACKNEY.\n\n\nMy young Friends,\n\nHaving drawn up the following _Heads of Lectures_ for your use, I take\nthe liberty thus publickly to dedicate them to you; and as I earnestly\nwish for your improvement and happiness in all respects, excuse me if I\ntake the farther liberty of making a few observations, and giving you\nsome advice, of a more general nature, adapted to your age and\ncircumstances.\n\nAs you will soon leave this place of education, and enter upon your\nseveral professions and employments, I hope your conduct will\ndemonstrate to the world the solid advantages of this institution, and\nthat the great expence attending it, and the best attention of the\nmanagers, have not been bestowed in vain.\n\nMany liberal friends of science, of virtue, and of religion, have\ncontributed to procure you the advantages which you enjoy. They have\nspared no pains to provide able and careful tutors, and you have had\nevery other advantage for the prosecution of your studies that they\ncould procure you, unclogged by any subscription to articles of faith,\nor obligation of any other kind, besides such as they have deemed\nnecessary for your own good, and to give the institution its greatest\neffect. This is an advantage you could not have found elsewhere, at\nleast in this country. And in every seminary of education much more\ndepends upon opportunity for study, free from any obstruction, and undue\nbias, than upon the ability of tutors; though there is an additional\nadvantage when they are able men, and eminent in the branches of science\nwhich they undertake to teach. But this is by no means so essential as\nmany other circumstances.\n\nWhatever be the qualifications of your tutors, your improvement must\nchiefly depend upon yourselves. They cannot _think_ or _labour_ for\nyou. They can only put you in the best way of thinking and labouring for\nyourselves. If, therefore, you get knowledge, you must acquire it by\nyour own industry. You must form all conclusions, and all maxims, for\nyourselves, from premises and _data_ collected, and considered by\nyourselves. And it is the great object of this institution to remove\nevery bias the mind can lie under, and give the greatest scope to true\nfreedom of thinking and inquiry. And provided you be intelligent and\nvirtuous men, and good citizens, it will be no cause of regret to the\nfriends of this institution, if, with respect to _religion_, or\n_politics_, you adopt systems of principles, and maxims of conduct, very\ndifferent from theirs.\n\nGive me leave, now that I am addressing you as _young men_, and young\n_students_, to suggest a caution on a subject, of the importance of\nwhich it is hardly possible that you should be sufficiently aware,\nbecause it is only impressed by that _experience_ which you have not yet\nhad. I mean that degree of vanity which generally accompanies the\nacquirements that diligent persons of your age make in places of liberal\neducation, and the contempt they are too apt to entertain for those who\nhave not made the same proficiency with themselves. And I assure you,\nthat in the observations I shall make on this subject, I have no view\nwhatever to any thing that I have observed, or heard, of any of you in\nparticular. But I have been in your situation myself, and I know the\nimportance of these observations to students in general.\n\nYou are now at an age in which young persons usually make the most\nsensible advances in knowledge, and in which the understanding appears\nto ripen the most rapid manner. You are able to say every year, every\nmonth, and almost every day, what particular advances you have made, and\nhow much you know more than you did before. And being taught, and\naccustomed, to express your thoughts in writing, you find yourselves\nqualified to do this in a manner of which you had no idea, or\nexpectation, but a little time ago. You also perfectly remember what you\nhave so recently learned, and many respects may be more particular and\nexact than even your tutors themselves.\n\nThe almost unavoidable effect of this is a high idea of your own powers\nand attainments, and too often a proportionable contempt of those who,\nnot having had equal advantages, cannot do what you are easily capable\nof. A certain degree of vanity is, therefore, excusable in young\npersons; and, indeed, it is by means of it that they are excited to\nexert themselves in a manner that they would not otherwise have done.\nBut be careful that this temper be not indulged to excess, for it will\nthen be found to have serious ill consequences; the least of which is\nthe precluding future improvement, from being already satisfied with\nyourselves, and conscious of a sufficient superiority over others.\n\nThe foundation of this self-conceit, on account of literary attainments,\nwill be found to be extremely weak. In fact, we learn more before the\nperiod to which you are now arrived, and I hope you will continue to\nlearn more after it, without its being so much noticed; and the\n_ability_ that is discovered in the acquirements which are the subjects\nof this vanity is not greater than appears on other occasions. Only they\nare not so conspicuous.\n\nWhat we all learn in the first three years of our lives, is much more\nextraordinary in its nature than all that we acquire afterwards. I mean\nthe perfect use of our limbs, and the elements of speech. What we learn\nin a month in that early period of life, could not, if we were brought\nup in the ignorance of it, be learned in a year at any subsequent\nperiod. But these acquirements being universal, and what the\ncircumstances in which we are all necessarily in compel us to learn, it\ndoes not appear extraordinary in any particular individual. Also, the\nproficiency that boys make at a grammar school, in which, in general,\nthe dead languages only are taught (a knowledge of which is commonly the\nresult of severe application) is too common to be the cause of much\nself-conceit. But the advances that are made at places of liberal\neducation are both less common, and of a more conspicuous nature.\n\nYou will also find, if you continue your application to study, that it\nis only the elements of science that you can acquire here, and that if\nyou live many years, they will bear but a small proportion to your\nfuture acquirements. But those future acquirements, in consequence of\ntheir bearing a less proportion to your whole stock of knowledge, will\nnot be so conspicuous. Thus, though all the buildings that in one year\nare added to such a city as London would make a pretty large country\ntown, they bear so small a proportion to what was built before, that\nthey are not much noticed; whereas, had half the quantity of building\nbeen erected in a place where no house had existed before, it would have\nbeen a memorable event in the history of the country.\n\nAlso, as in old cities many buildings will fall to decay, while new ones\nare added; you must expect to forget much of what you now know. No man\ncan give equal attention to every object; and as we advance in life,\nwe, in general, only learn new things at the expence of the old ones.\nBut then they are the more valuable articles of knowledge, the more\ngeneral and leading principles, which remain with us; while the more\nuseless ones, things to which we give less attention because we find\nthem to be of less use, disappear. Yet it is no uncommon thing for\ningenious students to despise old scholars who are not so ready in the\n_minutiae_ of literature, though they may have forgotten more than those\nyouths ever knew, and may retain what they cannot acquire without\nforgetting as much.\n\nAnother observation proper to lessen the conceit of literary men, is,\nthat genius is not confined to _them_, but is equally great, though not\nequally conspicuous, in every other line of life, and especially in\nmanufactures and the arts. Here, however, discoveries equal, with\nrespect to _sagacity_, to those of Newton, contribute little to\nposthumous fame, because the discoverers are not writers.\n\nBut the greatest branch of intellectual excellence with respect to\nwhich every other is nothing, and which, from its nature, can never be\nfoundation of any self-conceit, is _virtue_, or right dispositions of\nmind, leading to right conduct in life. Proper sentiments, and just\naffections of mind, arise from just, and often comprehensive, views of\nthings, past, present, and to come. And if the real greatness of any\nthought, or action, be estimated by the number of elements that\nconstitute it, and its remoteness from the dictates of sense and natural\nappetite, a virtuous and pious man will appear to be a much more\ndignified character, more proper to be viewed with admiration and\nesteem, than the greatest scholar; discovering, in fact, greater\ncomprehension and force of mind. I mean, however, that virtue which is\nthe result of reflection, of discipline, and much voluntary exertion,\nwhich, though operating with equal promptness and facility, is as much\nsuperior to mere _innocence_, and what is commonly called _good nature_,\nas motions secondarily automative are to those that are primarily so; a\ncomparison which you who have studied _Hartley's Theory of the Mind_\nwill see the force of.\n\nThese considerations I take the liberty to suggest, as being proper to\nlessen that vanity which is so incident to those who distinguish\nthemselves in the fields of literature, and which, operating like the\nacquisition of riches, or power, or any possession that is _rare_ among\nmen, instead of enlarging, may tend to contract the mind, by confining\nits attention to itself. Beginning with a generous emulation, it\nproceeds to envy and jealousy, and ends in actual hatred and malignity,\nagainst which you cannot, surely, be too strongly put upon your guard;\nthis being the greatest depravity to which human nature is subject, and\nwhich yet, like any other vice, may be in full possession of the mind,\nwithout the person himself knowing, or suspecting it; unless he give\nmore attention to his feelings than most persons do. If no man ever\nthought himself to be avaricious, or cruel, can it be expected that any\nperson should ever discover that he is too self-conceited?\n\nBetter, however, infinitely better, were it to rank with the merest\ndunces, than have the conceit and malignity (produced originally from\nconceit) of some who have distinguished themselves the most as\nlinguists, critics, and poets. Even the study of nature, though, from\nits vast extent, it is less apt to produce this baneful effect, is not\nalways a sufficient guard against it. This is an affecting and an\nalarming consideration. But in the intellectual, as in the civil and\ncommercial world, we gain nothing but at the risk of some loss; and in\nthis case the possible gain is worth the risk of even this great loss.\n\nFor when literary, and scientific excellence coincide with that which is\nof a moral nature, it adds unspeakably to the value of a character.\nIngenuity coupled with modesty, and great genius with benevolence and\ntrue piety, constitute the perfection of human character, and is what we\nshould ever have in view. And a course of education in which both these\nobjects are equally attended to, is the only one that deserves to be\ncalled _liberal_: but such as, I hope, you have found this to be.\n\nGive me leave further to observe to you, that the time that you spend in\na place of liberal education is of more importance to you than you can\nbe at present aware of. Whatever be the sphere of life for which you are\ndestined, the probability is, that you will hereafter have but little\nleisure for reading and studying, compared to what you have now.\nBesides, general maxims of all kinds, such as are the foundation of all\nour future conduct, in morals, religion, or politics, are generally\nformed at your time of life. From this period expect no great change in\nyour opinions, or conduct; because now it is that you give particular\nattention to the forming your opinions on all subjects of importance; so\nthat very little that is materially new to you can be expected to occur\nto you in future life, and almost every thing that you would choose to\nread will only tend to confirm you in the general principles that you\nwill now adopt. There are, no doubt, exceptions to this, as well as\nevery other general observation; but it is wisdom to suppose, and to act\nupon the supposition, that we are constituted as the generality of\nmankind are, and that we shall feel, and act, as they do. Since, then,\nso much depends on the leading principles and maxims which you will now\nadopt, be it your care to form just and good ones, and let no authority\nof tutors, or others, have any undue influence over you. In all cases\nthink and judge for yourselves, and especially on all subjects of\nimportance, and with as much attention as you can give to them.\n\nIt may not be amiss, in the present state of things, to say something\nrespecting another subject, which now commands universal attention. You\ncannot but be apprised, that many persons entertain a prejudice against\nthis College, on account of the republican, and, as they choose to call\nthem, the licentious, principles of government, which are supposed to be\ntaught here. Show, then, by your general conversation, and conduct, that\nyou are the friends of peace and good order; and that, whatever may be\nyour opinions with respect to the best form of government for people who\nhave no previous prejudices or habits, you will do every thing in your\npower for the preservation of that form of it which the generality of\nyour countrymen approve, and under which you live, which is all that can\nbe reasonably expected of any subject. As it is not necessary that every\ngood son should think his parent the wisest and best man in the world,\nbut it is thought sufficient if the son pay due respect and obedience to\nhis parent; so neither is it to be expected that every man should be of\nopinion that the form of government under which he happens to be born is\nthe best of all possible forms of government. It is enough that he\nsubmit to it, and that he make no attempt to bring about any change,\nexcept by fair reasoning, and endeavouring to convince his countrymen,\nthat it is in their power to better their condition in that respect, as\nwell as in any other. Think, therefore, speak, and write, with the\ngreatest freedom on the subject of government, particular or general,\nas well as on any other that may come before you. It can only be avowed\ntyranny that would prevent this. But at the same time submit yourselves,\nand promote submission in others, to that form of government which you\nfind to be most approved, in this country, which at present\nunquestionably is that by _King, Lords, and Commons_.\n\nAs to _religion_, we may, surely, be allowed to think and act entirely\nfor ourselves; in all cases obeying God and conscience rather than man.\nBut let us be thankful for the degree of liberty that we are allowed,\nthough it be not all that we are justly entitled to; and let us not use\nany other means than reason and argument in order to better our\ncondition. By this peaceable and steady conduct we shall at length\nconvince those who will hear reason, that we are entitled to greater\nconsideration; and doubt not but whatever is _true_ and _right_, will\nfinally prevail, and be universally established.\n\nThat any of your tutors, or any of the friends of this institution,\nwish to promote reformation, in church or state, by any other means than\nthose of reason, and argument, is a _calumny_, utterly void of\nfoundation, or probability. But your conduct, dispersed as you will soon\nbe in different parts of the country, will be the best means of refuting\nit. Let us leave the method of proceeding by _riot_ and _tumult_ to\nthose persons to whose schemes such proceedings are congenial. Truth\nstands in no need of such support, and will always triumph when assailed\nby such weapons. In return, then, for the advantages which you have\nenjoyed in this institution, do it this service; and in recommending it,\nI trust you are doing substantial service to the cause of liberty and\ntruth; and conferring a most important benefit on your country, and on\nmankind.\n\n\n\n\nCONTENTS.\n\n\nLECTURE I.\n_The Introduction_                                              1\n\nLECTURE II.\n_Of the Properties of all Matter_                               9\n_Of Aeriform Substances_                                       13\n\nLECTURE III.\n_Of Atmospherical Air_                                         15\n\nLECTURE IV.\n_Of Dephlogisticated Air_                                      18\n_Of Phlogisticated Air_                                        20\n\nLECTURE V.\n_Of Inflammable Air_                                           21\n\nLECTURE VI.\n_Of Nitrous Air_                                               23\n\nLECTURE VII.\n_Of Fixed Air_                                                 27\n_Of Hepatic Air_                                               29\n_Of Phosphoric Air_                                            30\n\nLECTURE VIII.\n_Of Dephlogisticated Marine Acid Air_                          31\n_Of Phlogisticated Marine Acid Air_                            32\n\nLECTURE IX.\n_Of Vitriolic Acid Air_                                        34\n_Of Fluor Acid Air_                                            36\n\nLECTURE X.\n_Of Alkaline Air_                                              37\n_Miscellaneous Observations relating to Air_                   38\n\nLECTURE XI.\n_Of Liquid Substances; and first of Water_                     41\n\nLECTURE XII.\n_Of the Nitrous Acid_                                          45\n\nLECTURE XIII.\n_Of the Vitriolic Acid_                                        49\n_Of the Marine Acid_                                           52\n\nLECTURE XIV.\n_Of the Vegetable Acids, and others of a less perfect nature_  54\n\nLECTURE XV.\n_Of the Phosphoric Acid_                                       59\n\nLECTURE XVI.\n_Of Alkalis_                                                   62\n\nLECTURE XVII.\n_Of Liquid Inflammable Substances_                             66\n_Of AEther_                                                     68\n\nLECTURE XVIII.\n_Of Oil_                                                       70\n\nLECTURE XIX.\n_Of Solid Substances_                                          76\n_Of Calcareous Earth_                                          77\n_Of Siliceous Earth_                                           79\n\nLECTURE XX.\n_Of Argillaceous Earth_                                        81\n_Of Terra Ponderosa_                                           82\n_Of Magnesia_                                                  83\n\nLECTURE XXI.\n_Of Ores_                                                      84\n_Of Gold_                                                      87\n\nLECTURE XXII.\n_Of Silver_                                                    90\n_Of Platina_                                                   92\n\nLECTURE XXIII.\n_Of Mercury_                                                   94\n\nLECTURE XXIV.\n_Of Lead_                                                      99\n_Of Copper_                                                   101\n\nLECTURE XXV.\n_Of Iron_                                                     105\n\nLECTURE XXVI.\n_Of Tin_                                                      109\n_Of the Semi-metals_                                          113\n\nLECTURE XXVII.\n_Of Nickel_                                                   115\n_Of Arsenic_                                                  116\n_Of Cobalt_                                                   118\n_Of Zinc_                                                     119\n\nLECTURE XXVIII.\n_Of Antimony_                                                 121\n_Of Manganese_                                                123\n_Of Wolfram_                                                  124\n_Of Molybdena_                                                125\n_Of Solid Combustible Substances_                             126\n\nLECTURE XXIX.\n_Of the Doctrine of Phlogiston and the Composition of Water_  127\n\nLECTURE XXX.\n_Of Heat_                                                     135\n\nLECTURE XXXI.\n_Of Animal Heat_                                              145\n\nLECTURE XXXII.\n_Of Light_                                                    148\n\nLECTURE XXXIII.\n_Of Magnetism_                                                155\n\nLECTURE XXXIV.\n_Of Electricity_                                              162\n\nLECTURE XXXV.\n_The same Subject continued_                                  170\n\nLECTURE XXXVI.\n_The same Subject continued_                                  177\n\n\n\n\nLECTURES ON EXPERIMENTAL PHILOSOPHY.\n\n\n\n\nLECTURE I.\n\n\n_The Introduction._\n\nThe object of experimental philosophy is the knowledge of nature in\ngeneral, or more strictly, that of the properties of natural substances,\nand of the changes of those properties in different circumstances. This\nknowledge can only be attained by _experiment_, or _observation_; as\nthat clay is capable of becoming hard by means of fire, and thereby\nbeing made into bricks, and that by the same means lime-stone can be\nconverted into quick-lime, and by the addition of water and sand, make\nmortar. It is by observation also that we discover that stones and other\nheavy bodies fall to the ground, and that a magnet will attract iron. In\nother words, experimental philosophy is an investigation of the wisdom\nof God in the works and _the laws of nature_, so that it is one of the\ngreatest objects to the mind of man, and opens a field of inquiry which\nhas no bounds; every advance we make suggesting new doubts and subjects\nof farther inquiry.\n\nThe uniformity we discover in the properties of natural substances\nenables us to lay down general rules, or principles, which, being\ninvariable, we call the laws of nature; and by our knowledge of these\nlaws we are able to predict, and at our own pleasure to produce,\nparticular results, and this is the source of all the powers of man. It\nis the direction we acquire of the powers of nature; so that, as Lord\nBacon observed, _knowledge is power_.\n\nAll arts and manufactures are derived from science. Thus the doctrine of\n_mechanics_ is an application of the law of gravitation. Every thing we\nare capable of doing by means of the steam-engine is derived from our\nknowledge of the properties of water in steam; all the great effects of\ngunpowder we owe to our knowledge of the composition, and chemical\nproperties, of that substance.\n\nEvery new appearance in nature is preceded by some new circumstance, and\nto this, or rather to something always attending it, we say that the\nappearance is _owing_. This circumstance we therefore call the _cause_,\nand the new appearance the _effect_ of that cause. Thus we say that the\nunion of phlogiston to a particular kind of earth is the cause of its\nbecoming a metal.\n\nIt is one of the principal rules of philosophizing to admit no more\ncauses than are necessary to account for the effects. Thus, if the power\nof gravity, by which heavy bodies fall to the earth, be sufficient to\nretain the planets in their orbits, we are authorized to reject the\n_Cartesian Vortices_. In other words, we must make no more general\npropositions than are necessary to comprehend all the particulars\ncontained in them. Thus, after having observed that iron consists of a\nparticular kind of earth united to phlogiston, and that it is soluble in\nacids; and that the same is true of all other metallic substances, we\nsay, universally, that all metals consist of a peculiar earth and\nphlogiston, and that they are all soluble in some acid.\n\nOf the circumstances which occasion a change in the properties of\nbodies, some are the addition of what are properly called _substances_,\nor things that are the objects of our senses, being _visible_,\n_tangible_, or having _weight_, &c. Thus the addition of an acid changes\nan alkali into a neutral salt. But other changes are occasioned either\nby a change of texture in the substance itself, or the addition of\nsomething that is not the object of any of our senses. Thus, a piece of\nsteel becomes a magnet by the touch of another magnet, and a drop of\nglass acquires the property of flying asunder by a small fracture, in\nconsequence of falling when red hot into cold water. Such also, in the\nopinion of some, is the difference between hot and cold substances.\n\nTill the nature of the cause be ascertained, it is convenient to make\nuse of the term _principle_, as including both of the above-mentioned\ncauses of the change of properties in bodies. Thus, whatever be the real\ncause of gravity, or of inflammability, we may speak of the _principle\nof gravity_, or of _inflammability_; whether, with Newton, we suppose\ngravity to be occasioned by a fluid pervading the whole universe, which\nhe termed _aether_, and whether inflammability be caused by the presence\nof a real substance called phlogiston, or not. In this manner we use the\nletters _x_ and _y_ to denote unknown quantities in algebra.\n\nWhen changes are made in substances by the addition of other substances,\nthey make what is called a _chemical union_; and in this case the\nproperties of the compound cannot with any certainty be deduced from\nthose of the component parts, but must be ascertained by fresh\nexperiments. Thus, from the specific gravities, or the degrees of\nfusibility, of two metals, those of the compound cannot be predicted.\nNeither water nor acid of vitriol will separately dissolve iron, so as\nto produce inflammable air, but both together will do it. However, the\nproperties of similar compounds are similar to one another. Thus, all\nmetals dissolved in acids are precipitated by mild alkalis. This\nchemical union of two substances we ascribe to a certain _elective\nattraction_, or _affinity_ that subsists between them, in consequence of\nwhich they unite with one another whenever a proper opportunity offers,\nin preference to those substances to which they were before united. Thus\nthe vitriolic acid, having a stronger affinity with the vegetable alkali\nwhich is the basis of nitre, will unite with that alkali, and with it\nform another compound, called _vitriolated tartar_, while the acid of\nnitre, being detached from its base, is collected separately.\n\nWhen two substances compose one liquid, and a third, which has a\nstronger affinity with either of the two parts than they have with each\nother, is added to them, it will unite with that part, and take its\nplace in the solution, while the other will in many cases be\nprecipitated, and may be collected. Thus the earth of alum is\nprecipitated from a solution of alum by salt of tartar. This is the case\nof _simple affinity_.\n\nWhen both the substances are compounds, the component parts of which\nhave a weaker affinity with each other than they have with those of the\nother compound, two new combinations are formed, and this is called a\ncase of _double affinity_. Thus when phlogisticated alkali is poured\ninto a solution of green vitriol, the acid of the vitriol unites with\nthe alkali, while the phlogiston joining the calx of iron makes Prussian\nblue.\n\nAll nature lying open to our investigation, we must consider the\ndifferent parts in some order. But it is not very material which we\nadopt, because, begin where we will, the properties of the substances we\nfirst treat of will be connected with those which must be particularly\nconsidered afterwards, the changes in one substance being occasioned by\nits union with another. It will be impossible, for example, to explain\nthe properties of metals without considering the _acids_, because by\ntheir union with acids very important changes are made in their\nproperties.\n\nThere have been three principal methods of arranging natural substances.\nOne is according to the _three kingdoms_, as they are called, into which\nthey have been distributed, viz. the _mineral_, the _vegetable_, and the\n_animal_. Another is according to the _elements_ which enter into their\ncomposition, and a third according to the _form_ in which they are\nusually found, viz. _aerial_, _fluid_, or _solid_. Upon the whole this\nlast appears to me to be the most convenient, especially as it is easy\nto intermix general observations concerning the other divisions when\nthey are particularly wanted. As there will be frequent occasion to\nspeak of the component and elementary parts of all substances, I shall\nhere observe, that, according to the latest observations, the following\nappear to be the elements which compose all natural substances, viz.\n_dephlogisticated air_, or the _acidifying principle_; _phlogiston_, or\nthe _alkaline principle_; the different _earths_, and the principles of\n_heat_, _light_, and _electricity_. Besides these, there are the\nfollowing principles which have not been proved to be substances, viz.\n_attraction_, _repulsion_, and _magnetism_. By the help of these\nprinciples we are able, according to the present state of natural\nknowledge, to explain all the appearances that have yet occurred to us.\n\n\n\n\nLECTURE II.\n\n\n_Of the Properties of all Matter._\n\nBefore I consider the properties of particular substances, it will be\nproper to mention those which are common to them all. But I shall first\nobserve, that the term _substance_ has no proper idea annexed to it, but\nis merely a convenience in speech; since we cannot speak of the\nproperties of substances, such as _hard_, _round_, _coloured_, &c. &c.\n(which circumstances alone affect our senses, and thereby give proper\nideas) without saying that they inhere in, or belong to, some _thing_,\n_substance_, or _substratum_. The terms _being_ and _person_ are also in\nthe same predicament.\n\nOne property of all substances is _extension_, since they all occupy\nsome portion of space.\n\nThe incapacity of any substance to change its place has been termed,\nthough improperly, the _vis inertiae_ of matter. It is sufficient to say,\nthat neither this, nor any other effect can be produced without a cause.\n\n_Infinite divisibility_ is a necessary property of all extended\nsubstance; and from this circumstance it will follow, that the smallest\nquantity of solid matter may be made to fill the largest space, and yet\nnone of the pores shall exceed the smallest given magnitude; and\nconsequently, that, for any thing we know to the contrary, all the\nbodies in the universe may be comprized in the smallest space.\n\nAnother property usually ascribed to all matter is _impenetrability_,\nor the necessary exclusion of any substance from the place occupied by\nanother. But the only proof of impenetrability is the _resistance_ that\nwe find to our endeavours to put one substance into the place of\nanother; and it is demonstrated by experiments, that this resistance is\nnot occasioned by the actual contact of the substances, but by a power\nof repulsion acting at a real distance from their surfaces. It requires\na considerable force to bring two solid substances into as near contact\nas the particles of the same substance; and that _these_ are not in\nactual contact is evident, from their being capable of being brought\nnearer by cold; and this is most remarkable with respect to the\nheaviest, that is, the densest, of all substances, viz. the metals.\n\nA more positive argument for the penetrability of matter is, that the\nparticles of light, after entering the densest transparent substance, do\nnot appear to meet with any obstruction to their progress till they come\nto the opposite side.\n\nThe powers of _attraction_ and _repulsion_ seem to be common to all\nmatter, and the component parts of all substances are kept in their\nplaces by the due balance of those opposite powers. If, by any means,\nthe particles of any substance be removed beyond their sphere of mutual\nattraction, they repel one another, as those of water when it becomes\nsteam.\n\nOf the different kinds of attraction, that of _gravitation_ seems to\nextend to the greatest possible distance; but that which keeps together\nthe parts of the same substance, thence called the _attraction of\ncohesion_, and the different kinds of chemical attractions, called\n_affinities_, only act at a small distance. Of the causes of these\nattractions we are entirely ignorant.\n\n\n_Of Aeriform Substances._\n\nAeriform substances, of which the air that we breathe is one, though\ninvisible, are real substances, as appears by their excluding other\nsubstances.\n\nThat the air has _weight_ appears by actually weighing a vessel before\nand after it is exhausted of air by means of an air-pump (an instrument\ncontrived for that purpose) by its bursting a bladder, and various other\nexperiments.\n\nAir, being a fluid, presses in all directions, as in the experiment of\nthe fountain in _vacuo_, and others.\n\nThe weight of the air is the cause of the suspension of mercury in a\nbarometer, and of the action of pumps. The weight of atmospherical air\nis to that of water in the proportion of about 1 to 800, so as to press\nwith the weight of about fourteen pounds on every square inch of\nsurface.\n\nAir, being an elastic fluid, is capable of occupying more or less space\naccording to the pressure which it sustains, as appears by a bladder\npartially filled with air being expanded when the air is drawn from a\nreceiver in which it is put, by means of the air-pump, and compressed in\nthe condensing engine, an instrument the reverse of the air-pump.\n\nAir is necessary to the conveyance of sound, to the existence of flame,\nand to animal life.\n\n\n\n\nLECTURE III.\n\n\n_Of Atmospherical Air._\n\nThe first species of air that offers itself to our consideration is that\nof the atmosphere, which appears to consist of a mixture of two kinds of\nair, of different and opposite qualities, viz., dephlogisticated and\nphlogisticated, in the proportion of about one third of the former to\ntwo thirds of the latter. It is by means of the former of these two\ningredients that it is capable of supporting flame and animal life.\n\nThis composition of atmospherical air is proved by several substances\nabsorbing the dephlogisticated air, and leaving the phlogisticated. All\nthese processes have been termed _phlogistic_, because the effect is not\nproduced but by substances supposed to contain phlogiston in a volatile\nstate; and by the affinity between phlogiston and the dephlogisticated\npart of the air, the one is separated from the other. Of these processes\nare the calcination of metals, a mixture of iron-filings and sulphur,\nliver of sulphur, the burning of phosphorus, and the effluvia of\nflowers.\n\nIn some cases, however, it is not so clear that any thing is emitted\nfrom the substance that produces this effect; for water deprived of all\nair will absorb the dephlogisticated part of the atmospherical in\npreference to the phlogisticated part.\n\nAs the purity of atmospherical air, or its fitness for respiration,\ndepends upon the proportion of the dephlogisticated air that it\ncontains, any of the above-mentioned processes will suffice to determine\nit. The more any given quantity of air is diminished by any of them, the\npurer it was before the diminution. But this effect is produced the most\nquickly by a mixture of nitrous air, or firing inflammable air in it,\nbeing almost instantaneous.\n\nIn order to measure the purity of air, it is convenient to take more of\nthe nitrous or inflammable air than is necessary to saturate the\ndephlogisticated air it contains. Equal quantities of each best answer\nthe purpose. Supposing a given quantity of atmospherical air to be mixed\nwith an equal quantity of nitrous air, and the residuum to be 1.1\nmeasure, the proportion of dephlogisticated and phlogisticated air in it\nmay be found by the following arithmetical operation, it being here\ntaken for granted that one measure of pure dephlogisticated air will\nsaturate two measures of pure nitrous air.\n\n      2.0 viz. one of each.\n      1.1 the residuum.\n     -----\n    3)0.9 the quantity that has disappeared.\n      0.3 the dephlogisticated air contained\n            in the measure of the air examined.\n\nAnd this substracted from 1 leaves .7 for the proportion of\nphlogisticated air in it.\n\n\n\n\nLECTURE IV.\n\n\n_Of Dephlogisticated Air._\n\nDephlogisticated air, which is one of the component parts of\natmospherical air, is a principal element in the composition of acids,\nand may be extracted by means of heat from many substances which contain\nthem, especially the nitrous and vitriolic; as from nitre, red\nprecipitate, the vitriols, and turbith mineral, and also from these two\nacids themselves, exposed to a red heat in an earthen tube. This kind of\nair is also contained in several substances which had attracted it from\nthe atmosphere, as from precipitate _per se_, _minium_, & _manganese_.\n\nDephlogisticated air is likewise produced by the action of light upon\ngreen vegetables; and this seems to be the chief means employed by\nnature to preserve the purity of the atmosphere.\n\nIt is this ingredient in atmospheric air that enables it to support\ncombustion and animal life. By means of it the most intense heat may be\nproduced, and in the purest of it animals will live nearly five times as\nlong as in an equal quantity of atmospherical air.\n\nIn respiration, part of this air, passing the membrane of the lungs,\nunites with the blood, and imparts to it its florid colour, while the\nremainder, uniting with phlogiston exhaled from the venous blood, forms\nfixed air. It is dephlogisticated air combined with water that enables\nfishes to live in it.\n\nDephlogisticated air is something heavier than atmospherical air, and\nthe purity of it measured by mixing with it two equal quantities of\nnitrous or inflammable air, deducing the residuum after the diminution\nfrom the three measures employed, and dividing the remainder by 3, as in\nthe process for common air.\n\n\n_Of Phlogisticated Air._\n\nThe other ingredient in the composition of atmospherical air is\nphlogisticated air. It is procured by extracting the dephlogisticated\npart of the common air, as by the calcination of metals, &c. &c. by\ndissolving animal substances in nitrous acid, and also by the union of\nphlogiston with nitrous air, as by heating iron in it, and by a mixture\nof iron-filings and sulphur.\n\nPhlogisticated air extinguishes a candle, is entirely unfit for\nrespiration, and is something lighter than common air. It is not capable\nof decomposition, except by exploding it together with a superabundance\nof dephlogisticated air, and a quantity of inflammable air, or by taking\nthe electric spark repeatedly in a mixture of it and dephlogisticated\nair. In these cases nitrous acid is formed.\n\n\n\n\nLECTURE V.\n\n\n_Of Inflammable Air._\n\nInflammable air is procured from all combustible substances by means of\nheat and water, and from several of the metals, especially iron, zink,\nand tin, by the vitriolic and marine acids.\n\nFrom oils and spirit of wine it is procured by the electric spark. By\nthe same means also alkaline air is converted into it.\n\nThat which is procured from metals, especially by steam, is the purest\nand the lightest, about ten times lighter than common air; in\nconsequence of which, if a sufficient quantity be confined in a light\ncovering, it is possible to make it carry up heavy weights.\n\nWhen it is procured from animal or vegetable substances, it is of a\nheavier kind, and burns with a lambent flame, of various colours,\naccording to the circumstances.\n\nCalces of metals heated in inflammable air are revived, and the air\nabsorbed; and since all the metals are revived in the same inflammable\nair, the principle of metallization, or _phlogiston_, appears to be the\nsame in them all.\n\nPure inflammable air seems to consist of phlogiston and water, and the\nlambent kinds to be the same thing, with the addition of some oily\nvapour diffused through it.\n\n\n\n\nLECTURE VI.\n\n\n_Of Nitrous Air._\n\nNitrous air is procured by dissolving most of the metals, especially\niron, mercury, and copper, in the nitrous acid; but that from mercury\nseems to be the purest. Nitrous air produced from copper contains a\nmixture of phlogisticated air. Some nitrous air is also obtained from\nthe solution of all vegetable substances in nitrous acid; whereas animal\nsubstances in the same process yield chiefly phlogisticated air: but in\nboth these cases there is a mixture of fixed air.\n\nThis species of air is likewise produced by impregnating water with\nnitrous vapour. This process continues to have this effect after the\nwater becomes blue, but ceases when it turns green; there not then,\nprobably, being a sufficient proportion of water. Nitrous air is\nlikewise produced by volatile alkali passing over red hot manganese, or\ngreen vitriol, when they are yielding dephlogisticated air. This shews\nthat dephlogisticated air is one ingredient in the composition of\nnitrous air, and the same thing appears by pyrophorus burning in it. On\nthe contrary, when nitrous air is made to pass over red-hot iron,\nvolatile alkali is produced.\n\nNitrous air is completely decomposed by a mixture of about half its bulk\nof dephlogisticated air, and the produce is nitrous acid. And as nitrous\nacid is likewise formed by the union of inflammable and dephlogisticated\nair, one principal ingredient in nitrous air must be common to it and\ninflammable air, or phlogiston. This air is likewise decomposed by\ndephlogisticated nitrous acid, which by this means becomes\nphlogisticated. It is also decomposed by a solution of green vitriol,\nwhich by this means becomes black, and when exposed to the air, or\nheated, emits nitrous air, and recovers its former colour. These\ndecompositions of nitrous air seem to be effected by depriving it of\nphlogiston, and thereby reducing it to the phlogisticated air originally\ncontained in it.\n\nThis kind of air is diminished to about one fourth of its bulk by a\nmixture of iron filings and brimstone, or by heating iron in it, or\ncalcining other metals in it, when the remainder is phlogisticated air.\nAll that iron gets in this process is an addition of weight, which\nappears to be water, but it loses its phlogiston, so that nitrous air\nseems to contain more phlogiston, and less water than phlogisticated\nair.\n\nNitrous air and dephlogisticated air will act upon one another through a\nbladder, but in this case there remains about one-fourth of the bulk of\nnitrous air, and that is phlogisticated air; so that in this case there\nseems to be a conversion of nitrous air into phlogisticated air without\nany addition of phlogiston.\n\nNitrous air is decomposed by pyrophorus, and by agitation in olive oil,\nwhich becomes coagulated by the process. It is also absorbed by spirit\nof turpentine, by ether, by spirit of wine, and alkaline liquors.\n\nIt is imbibed by charcoal, and both that air which is afterwards\nexpelled from it by heat, and that which remains unabsorbed, is\nphlogisticated air.\n\nNitrous air resists putrefaction, but is diminished by the animal\nsubstances exposed to it to about a fourth of its bulk, and becomes\nphlogisticated air. It is likewise fatal to plants, and particularly to\ninsects.\n\nWhen nitrous air is long exposed to iron, it is diminished and brought\ninto a state in which a candle will burn in it, though no animal can\nbreathe it. But this peculiar modification of nitrous air, called\n_dephlogisticated nitrous air_, is produced with the greatest certainty\nby dissolving iron in spirit of nitre saturated with copper,\nimpregnating water with this air, and then expelling it from the water\nby heat. If bits of earthen ware be heated in this dephlogisticated\nnitrous air, a great proportion of it becomes permanent air, not\nmiscible with water, and nearly as pure as common air, so that the\nprinciple of _heat_ seems to be wanting to constitute it permanent air.\n\n\n\n\nLECTURE VII.\n\n\n_Of Fixed Air._\n\nHaving considered the properties of those kinds of air which are not\nreadily absorbed by water, and therefore may be confined by it, I\nproceed to those which _are_ absorbed by it, and which require to be\nconfined by mercury. There are two kinds, however, in a middle state\nbetween these, being absorbed by water, but not very readily; a\nconsiderable time, or agitation, being necessary for that purpose. The\nfirst of these is _fixed air_.\n\nThis kind of air is obtained in the purest state by dissolving marble,\nlime-stone, and other kinds of mild calcareous earth in any acid. It is\nalso obtained by the burning, or the putrefaction, of both animal and\nvegetable substances, but with a mixture of both phlogisticated and\ninflammable air. Fixed air is also produced by heating together iron\nfilings and red precipitate; the former of which would alone yield\ninflammable air, and the latter dephlogisticated. Fixed air is therefore\na combination of these two kinds of air.\n\nAnother fact which proves the same thing is, that if charcoal of copper\nbe heated in dephlogisticated air, almost the whole of it will be\nconverted into fixed air. On the same principle fixed air is produced\nwhen iron, and other inflammable substances, are burned in\ndephlogisticated air, and also when minium, and other substances\ncontaining dephlogisticated air, are heated in inflammable air.\n\nThat water is an essential part of fixed air is proved by an experiment\nupon _terra ponderosa aerata_, which yields fixed air when it is\ndissolved in an acid, but not by mere heat. If steam, however, be\nadmitted to it in that state, it will yield as much fixed air as when it\nis dissolved in an acid.\n\nWater absorbs something more than its own bulk of fixed air, and then\nbecomes a proper acid. Iron dissolved in this water makes it a proper\nchalybeate; as without iron it is of the same nature with Pyrmont or\nSeltzer water, which by this means may be made artificially.\n\nIce will not imbibe this air, and therefore freezing expels it from\nwater.\n\nFixed air extinguishes flame, and is fatal to animals breathing in it.\nAlso water impregnated with this air is fatal to fishes, and highly\ninjurious to plants. But water thus impregnated will prevent, in a great\nmeasure, the putrefaction of animal substances.\n\nFixed air thrown into the intestines, by way of glyster, has been found\nto give relief in some cases of putrid disease.\n\n\n_Of Hepatic Air._\n\nAnother species of air absorbed by water, but not instantly, is termed\n_hepatic air_, being produced by the solution of liver of sulphur, or of\nsulphurated iron, in vitriolic or marine acid.\n\nWater imbibes about twice its bulk of this kind of air, and it is then\nthe same thing with the sulphureous waters of Harrowgate.\n\n\n_Of Phosphoric Air._\n\nPhosphoric air is produced by the solution of phosphorus in caustic\nfixed alkali. If this air be confined by mercury, it will take fire on\nbeing admitted to atmospheric, and much more to dephlogisticated air.\nAfter agitation in water it loses this property, and the residuum is\nmerely inflammable air, with no great diminution of its bulk. This kind\nof air, therefore, probably consists of phosphorus dissolved in\ninflammable air; though it cannot be made by melting it in inflammable\nair.\n\n\n\n\nLECTURE VIII.\n\n\n_Of Dephlogisticated Marine Acid Air._\n\nThis species of air is produced by heating spirit of salt with\nmanganese; or more readily, by pouring acid of vitriol on a mixture of\nsalt and manganese, in the proportion of about 16 of the former to 6 of\nthe latter. In this case the acid of vitriol decomposes the salt, and\nthe marine acid, disengaged in the form of air, takes dephlogisticated\nair from the manganese; so that this species of air seems to consist of\nmarine acid vapour, and dephlogisticated air.\n\nThis species of air has a peculiarly pungent smell, and is absorbed by\nwater as readily as fixed air.\n\nThe water takes about twice its bulk of it; and thereby acquires a\nyellowish tinge. Both this air, and the water impregnated with it,\ndischarges vegetable colours from linen or cotton, and is thereby\nuseful in bleaching.\n\nThis air when cold coagulates into a yellowish substance. It dissolves\nmercury, and with it forms _corrosive sublimate_.\n\n\n_Of Phlogisticated Marine Acid Air._\n\nBesides the preceding kinds of air which are slowly absorbed by water,\nthere are others which are absorbed by it very rapidly, so that they\ncannot be confined but by mercury.\n\nOf this kind is _phlogisticated marine acid air_, procured by the acid\nof vitriol and common salt; the former seizing upon the alkaline basis\nof the latter, and thereby expelling the marine acid in the form of air.\n\nIt is called _phlogisticated_ to distinguish it from _dephlogisticated\nmarine acid air_, which seems to be the same thing, with the addition of\ndephlogisticated air.\n\nPhlogisticated marine acid air is heavier than common air. It\nextinguishes a candle with a blue flame. It dissolves many substances\ncontaining phlogiston, as iron, dry flesh, &c. and thereby forms a\nlittle inflammable air. Water absorbs 360 times its bulk of this air,\nand is then the strongest spirit of salt. It absorbs one-sixth more than\nits bulk of alkaline air, and with it forms the common sal ammoniac. Its\naffinity to water enables it to dissolve ice, and to deprive borax,\nnitre, and other saline substances, of the water that enters into their\ncomposition.\n\n\n\n\nLECTURE IX.\n\n\n_Of Vitriolic Acid Air._\n\nVitriolic acid air is procured by heating in hot acid of vitriol almost\nany substance containing phlogiston, especially the metals which are\nsoluble in that acid, as copper, mercury, &c. This kind of air is\nheavier than common air, and extinguishes a candle, but without any\nparticular colour of its flame. It will not dislodge the nitrous or\nmarine acids from any substance containing them.\n\nBy its affinity to water it deprives borax of it.\n\nOne measure of this air saturates two of alkaline air, and with it forms\nthe vitriolic ammoniac.\n\nWater imbibes between 30 and 40 times its bulk of this air, and retains\nit when frozen. Water thus impregnated dissolves some metals, and\nthereby yields inflammable air.\n\nIf this water be confined in a glass tube, together with common air, and\nbe exposed to a long continued heat, it forms real sulphur, the\ndephlogisticated part of the common air being imbibed, and forming real\nvitriolic acid, which uniting with the phlogiston in the air, forms the\nsulphur. Also this air mixed with atmospheric air will, without heat,\nimbibe some part of it, and thereby become the common acid of vitriol;\nso that water impregnated with vitriolic acid air, commonly called\n_sulphureous_, or _phlogisticated acid of vitriol_, wants\ndephlogisticated air to make it the common acid of of vitriol.\n\nThis kind of air is imbibed by oils, which thereby change their colour;\nwhale oil becoming red, olive oil of an orange colour, and spirit of\nturpentine of the colour of amber.\n\nIf this air be confined in a glass tube by mercury, and the electric\nspark be taken in it, a black tinge will be given to the glass\ncontiguous to the spark, and this black substance appears to be mercury\nsuper-phlogisticated; since by exposure to air it becomes running\nmercury: so that the vapour of mercury must be diffused through every\npart of this air, to the distance of at least several feet from the\nsurface of the mercury.\n\n\n_Of Fluor Acid Air._\n\nFluor acid air is procured by dissolving the earthy substance called\n_fluor_ in vitriolic acid.\n\nThis kind of air extinguishes a candle, and, like vitriolic acid air,\none measure of it saturates two of alkaline air. It is peculiar to this\nkind of air to dissolve glass when it is hot.\n\nIt seems to consist of a peculiar acid vapour united to the stony\nsubstance of the fluor; for water being admitted to it absorbs the acid\nvapour, and the stony substance is deposited. By this means it exhibits\nan amusing appearance, whether water be admitted to a glass jar\npreviously filled with that air, or the bubbles of air be admitted, as\nthey are formed, to a quantity of water resting on mercury.\n\n\n\n\nLECTURE X.\n\n\n_Of Alkaline Air._\n\nAlkaline air is produced by means of heat from caustic volatile alkali,\nand also from a mixture of sal-ammoniac and slaked lime, in the\nproportion of about one-fourth of the former to three-fourths of the\nlatter. In this case the marine acid in the sal-ammoniac unites with the\ncalcareous earth, and the volatile alkali (probably with the assistance\nof the water) takes the form of air.\n\nThis species of air is heavier than inflammable air, but lighter than\nany of the acid airs. Like them, however, it dissolves ice, and\ndeprives alum, and some other saline substances, of the water which they\ncontain. United with fixed air, it makes the concrete volatile alkali;\nwith marine acid air, the common sal-ammoniac; and with water, the\ncaustic volatile alkali.\n\nThe electric spark, or a red heat, converts alkaline air into three\ntimes its bulk of inflammable air; and the calces of metals are revived\nin alkaline, as well as in inflammable air; but there remains about\none-fourth of its bulk of phlogisticated air. These facts shew that\nalkaline air consists chiefly of phlogiston.\n\n\n_Miscellaneous Observations relating to Air._\n\nThe _nitrous_ acid may be exhibited in the form of air, as well as the\nvitriolic, the marine, and the fluor acids. But it cannot be confined\neven by mercury, which it instantly dissolves. It may, however, in some\nmeasure, be confined in a dry glass vessel, from which it will in a\ngreat measure expel the common air. This nitrous acid air is that red\nvapour, which is produced by the rapid solution of bismuth, and some\nother metals in the nitrous acid. But the vegetable acid cannot be\nexhibited in the form of air. It is only capable of being converted into\nvapour, like water: and in the common temperature of our atmosphere,\nreturns to a state of fluidity.\n\nDifferent kinds of air which have no affinity to each other, when once\nmixed together will not separate, notwithstanding any difference of\nspecific gravity. Such is the case of a mixture of inflammable and\ndephlogisticated air, and even of inflammable and fixed air. Without\nthis property also, the phlogisticated air, which constitutes the\ngreatest part of our atmosphere, being specifically lighter than\ndephlogisticated air, of which the other part of it consists, would\nseparate from it, and ascend into the higher regions of the atmosphere.\nInflammable air, however, will not mix with acid or alkaline air.\n\nDifferent kinds of air are expanded differently by the same degrees of\nheat; dephlogisticated air the least, and alkaline air the most.\n\nIf any fluid, as water, spirit of wine, or even mercury, be heated in a\nporous earthen vessel, surrounded by any kind of air, the vapour of the\nfluid will pass through the vessel _one_ way, while the air passes the\n_other_; and when the operation ceases, with respect to the _one_, it\nlikewise ceases with respect to the _other_.\n\n\n\n\nLECTURE XI.\n\n\n_Of Liquid Substances_;\n\nAND FIRST OF\n\n_WATER_.\n\nHaving considered all the substances that are usually found in the form\nof _air_, I come to those that are generally in a _fluid_ form,\nbeginning with _water_, which is the principal, if not the only cause of\nfluidity to all the other substances that I shall place in this class.\n\nPure water is a liquid substance, transparent, without colour, taste, or\nsmell; and with different degrees of heat and cold may be made to assume\nthe three forms of a solid, of a fluid, and of air. Below 32 deg. of\nFahrenheit it is ice, and above 212 deg. it is vapour; so that in an\natmosphere below 32 deg. it never could have been known to be any thing else\nthan a peculiar kind of stone, and above 212 deg. a peculiar species of\nair.\n\nIn passing from the state of a solid to that of a liquid, water absorbs\na great quantity of the principle, or matter, of _heat_, which remains\nin it in a _latent_ state; and in passing from a state of fluid to that\nof vapour, it absorbs much more; and this heat is found when the\nprocesses are reversed. It has been observed, that when water becomes\nvapour, it takes the form of small globules, hollow within, so as to be\nspecifically lighter than air.\n\nThe degree of heat at which water is converted into vapour depends upon\nthe pressure of the atmosphere; so that in vacuo, or on the top of a\nhigh mountain, it boils with little heat; and when compressed, as in\nPapin's digester, or in the bottom of a deep pit, it requires much heat.\nIn the former case the restoring of the pressure will instantly put a\nstop to the boiling, and in the latter case the removing of the pressure\nwill instantly convert the heated water into vapour.\n\nThe ease with which water is converted into vapour by heat, has given a\ngreat power to mechanicians, either by employing the natural pressure of\nthe atmosphere, when steam is condensed under a moveable pistern, in an\niron cylinder, which was the principle of the old fire-engine, or by\nemploying the elastic power of steam to produce the same effect, which\nis the principle of Mr. Watt's steam engine.\n\nWater was long thought to be incompressible by any external force, but\nMr. Canton has shewn that even the pressure of the atmosphere will\ncondense it very sensibly.\n\nWe do not know any external force equal to that by which water is\nexpanded when it is converted into ice, or into vapour. For though the\nparticles of water approach nearer by cold, yet when it crystallizes,\nthe particles arrange themselves in a particular manner, with\ninterstices between them; so that, on the whole, it takes up more room\nthan before.\n\nWater has an affinity to, and combines with, almost all natural\nsubstances, aerial, fluid, or solid; but most intimately with acids,\nalkalies, calcareous earth, and that calx of iron which is called\n_finery cinder_, from which the strongest heat will not expel it.\n\nIt has been supposed by some, that by frequent distillation, and also by\nagitation, water may be converted into a kind of earth; but this does\nnot appear to be the case. It has also of late been thought, that water\nis resolvable into dephlogisticated and inflammable air; but the\nexperiments which have been alleged to prove this do not satisfy me; so\nthat, for any thing that appeared till very lately, water might be\nconsidered as a simple element. By means of heat, however, it seems to\nbe resolvable into such air as that of which the atmosphere consists,\nviz. dephlogisticated and phlogisticated, only with a greater proportion\nof the former.\n\nWater, with respect to specific gravity and temperature, has generally\nbeen made the standard to all other substances; its freezing and boiling\npoints being the limits by means of which thermometers are graduated.\nOther substances have also been compared with water, as a standard,\nwith respect to the capacity of receiving heat, and retaining it in a\nlatent state, as will be shewn when we consider the subject of heat.\n\n\n\n\nLECTURE XII.\n\n\n_Of the Nitrous Acid._\n\nUnder the head of _liquids_ I shall consider _acids_ and _alkalis_,\nthough some of them may be exhibited in the form of air, and others in a\nsolid form. These two chemical principles are formed to unite with one\nanother, and then they constitute what is called a _neutral salt_.\n\nBoth acids and alkalis are distinguishable by their taste. Another test,\nand more accurate, is, that acids change the blue juices of vegetables\nred, and alkalis turn the syrup of violets green.\n\nAcids are generally distinguished according to the three kingdoms to\nwhich they belong, viz. _mineral_, _vegetable_, and _animal_. The\nmineral acids are three, the _nitrous_, the _vitriolic_, and the\n_marine_.\n\nThe nitrous acid is formed by the union of the purest inflammable air,\nor the purest nitrous air, with dephlogisticated air. But it is usually\nprocured from nitre by means of the vitriolic acid, which, seizing its\nbase, expels the nitrous acid in a liquid form. On this account this\nacid is said to be weaker than the vitriolic.\n\nIf the nitrous acid be made to pass through a red-hot earthen tube, it\nwill be decomposed, and the greatest part of it be converted into\ndephlogisticated air.\n\nLike all other acids, the nitrous acid has a strong affinity to water;\nbut it is not capable of so much concentration as the vitriolic. It is\ngenerally of an orange or yellow colour; but heat will expel this colour\nin the form of a red vapour, which is the same acid in the form of air,\nand loaded with phlogiston; and therefore when it is colourless it is\nsaid to be dephlogisticated. But the colourless vapour exposed to heat,\nor to light, will become coloured again; and the liquid acid imbibing\nthis coloured vapour, becomes coloured as before. This acid tinges the\nskin of a yellow colour, which does not disappear till the epidermis be\nchanged.\n\nThe nitrous acid unites with phlogiston, alkalis, metallic substances,\nand calcareous earth.\n\nBy means of its affinity with phlogiston it occasions that rapid\naccension called _detonation_, when any salt containing this acid,\nespecially nitre, is applied to hot charcoal, or when charcoal is put to\nhot nitre. In fact, the charcoal burns so rapidly by means of the\ndephlogisticated air supplied by the nitre.\n\nA mixture of sulphur assists the accension of these substances, and\nmakes gunpowder, in the explosion of which much nitrous or\nphlogisticated air is suddenly produced, and expanded by the heat. The\napplication of this force, both to useful and destructive purposes, is\nwell known. If, instead of nitre, a salt made with dephlogisticated\nmarine acid be made use of, the explosion is more easily produced, and\nis much more violent. Friction will do this as well as heat.\n\nNitre also enters into the composition of _pulvis fulminans_, viz. three\nparts nitre, two of dry alkali, and one of sulphur. This composition\nmelts, and yields a blue flame, before it explodes.\n\nBy means of the affinity of the nitrous acid to _oil_, another substance\ncontaining phlogiston, it is capable of producing not only a great heat,\nbut even a sudden flame, especially when mixed with a little vitriolic\nacid.\n\nNitrous acid dissolves all metallic substances except gold and platina,\nand in the solution nitrous air is produced.\n\nThe particular kinds of saline substances formed by the union of the\nnitrous acid with the several metals and earths may be seen in tables\nconstructed for the purpose. They are all deliquescent.\n\n\n\n\nLECTURE XIII.\n\n\n_Of the Vitriolic Acid._\n\nThe vitriolic acid, so called because it was originally procured from\n_vitriol_, is now generally procured from sulphur; the dephlogisticated\npart of the air uniting with it in the act of burning.\n\nThat dephlogisticated air is essential to this acid is evident from the\ndecomposition of it; for if the vapour of it be made to pass through a\nred-hot earthen tube, a great quantity of dephlogisticated air is\nprocured.\n\nThis acid has a strong affinity to water, with which it unites with much\nheat; and it is capable of greater concentration, or of being made\nspecifically heavier, than any other acid. When pure, it is entirely\nfree from colour and smell, owing, probably, to its being free from\nphlogiston, which is inseparable from the nitrous or marine acids.\n\nThe vitriolic acid will dislodge the nitrous, or marine, or any other\nacid, from their earthy or metallic bases; from which property it is\ncalled the strongest of all the acids.\n\nBy means of the superior affinity of the vitriolic acid to earths, and\nespecially to _terra ponderosa_, the smallest quantity of it in water\nmay be discovered by a solution of this earth in the marine acid. In\nthis acid the terra ponderosa is held in perfect solution; but with the\nvitriolic acid it forms a substance that is insoluble in water, and\ntherefore it instantly appears in the form of a white cloud.\n\nPerhaps chiefly from the strong affinity which this acid has with water,\n_pyrophorus_, consisting of a mixture of alum and several substances\ncontaining phlogiston, takes fire spontaneously on exposure to the air.\nIt is commonly made of three parts of alum and one of brown sugar, or of\ntwo parts alum, one of salt of tartar, and one of charcoal. They must be\nheated till they have for some time emitted a vapour that burns with a\nblue flame.\n\nThe saline substances produced by the union of this acid with the\nseveral earths and metals, are best exhibited in tables constructed for\nthe purpose. When united to three of the metals, viz. iron, copper, and\nzinc, they are called _vitriols_, green, blue, and white. And all the\nsubstances which this acid unites with crystallize, and do not\ndeliquesce.\n\nThis acid unites with oil, and the mixture is always black.\n\nWhen any substance containing phlogiston is heated in the vitriolic\nacid, another species of the acid, called _sulphureous_, is formed, of a\npungent smell. In reality, it is water impregnated with vitriolic acid\nair. It makes, however, a distinct species of acid, and is dislodged\nfrom its base by most of the others.\n\n\n_Of the Marine Acid._\n\nThe marine acid is procured from common salt by the vitriolic acid,\nwhich unites with its base, the fossil alkali.\n\nThis acid is generally of a straw-colour; but this is owing to an\nimpregnation with some earthy matter, most of which it readily\ndissolves, especially the metallic ones. It is less capable of\nconcentration than the vitriolic or nitrous acids, perhaps from a more\nintimate union of phlogiston with it. No heat can extract from it any\ndephlogisticated air.\n\nThough this is denominated a weaker acid than the nitrous, yet it will\ntake silver, lead, or mercury, from their union with the nitrous acid.\nUpon this principle, a solution of these metals in the nitrous acid will\nreadily discover whether any water contains the marine acid, the latter\nuniting with the metal dissolved in the former, and forming with it, if\nit be silver, a _luna cornea_; which being a substance insoluble in\nwater, discovers itself by a cloudy appearance.\n\nThe union of the marine acid with earths forms salts that easily\ndeliquesce, but with the metals such as are capable of crystallization;\nand so also is that formed by the union of this acid to terra ponderosa.\n\nNeither this acid nor the nitrous will dissolve gold or platina; but a\nmixture of them, called _aqua regia_, will do it.\n\nThe marine acid has a strong affinity to dephlogisticated air, and will\ntake it from manganese and other substances; and with this union it\nbecomes a different acid, called _dephlogisticated marine acid_, being\nwater impregnated with dephlogisticated marine acid air, described\nabove.\n\n\n\n\nLECTURE XIV.\n\n\n_Of the Vegetable Acids, and others of a less perfect nature._\n\nThe principal of the vegetable acids are the _acetous_ and the\n_tartareous_. The acetous acid is the produce of a peculiar fermentation\nof vegetable substances, succeeding the _vinous_, in which ardent spirit\nit is procured, and succeeded by the _putrefactive_, in which volatile\nalkali is generated.\n\nThus wine is converted into vinegar. Crude vinegar, however, contains\nsome ingredient from the vegetable substances from which it was\nprocured: but distillation separates them, and makes the vinegar\ncolourless; though some of the acid is lost in the process.\n\nThe acetous acid is concentrated by frost, which does not affect the\nproper acid, but only the water with which it is united. It may likewise\nbe concentrated by being first combined with alkalies, earths, or\nmetals, and then dislodged by a stronger acid, or by mere heat. Thus the\nacetous acid, combined with vegetable alkali, forms a substance that is\ncalled the _foliated earth of tartar_; and it may be expelled from it by\nthe vitriolic acid. When combined with copper it makes _verdigris_; and\nfrom this union heat alone will expel it in a concentrated state. The\nacetous acid thus concentrated is called _radical vinegar_. Still,\nhowever, it is weaker than any of the preceding mineral acids.\n\nSeveral vegetables, as lemons, sorrel, and unripe fruit, contain acids,\nready formed by nature, mixed with some of the essential oil of the\nplants, which gives them their peculiar flavours. All these acids have\npeculiar properties; but it is not necessary to note them in this very\ngeneral view of the subject. Like vinegar, these acids may be\nconcentrated by frost, and also by a combination with other substances,\nand then expelled by a stronger acid.\n\nThe _acid of tartar_ is very similar to that of vinegar. Tartar, from\nwhich it is procured, is a substance deposited on the inside of\nwine-casks, though it is also found ready formed in several vegetables.\nIt consists of the vegetable alkali and this peculiar acid. When refined\nfrom its impurities, it is called _crystals_, or _cream of tartar_. The\nacid is procured by mixing the tartar with chalk, or lime, which imbibes\nthe superfluous acid, and this is expelled by the acid of vitriol. Or it\nmay be procured by boiling the tartar with five or six times its weight\nof water, and then putting the acid of vitriol to it. This unites with\nthe vegetable alkali, and forms vitriolated tartar; and the pure acid of\ntartar may be procured in crystals, by evaporation and filtration, equal\nin weight to half the cream of tartar. This acid of tartar is more\nsoluble in water than the cream of tartar.\n\nThis acid, united to the mineral alkali, makes _Rochelle salt_.\n\nEvery kind of wood, when distilled, or burned, yields a peculiar acid;\nand it is the vapour of this acid that is so offensive to the eyes in\nthe smoke of wood.\n\nA peculiar acid is obtained from most vegetable substances, especially\nthe farinaceous ones, and from sugar, by distillation with the nitrous\nacid. This seizes upon the substance with which the acid was united, and\nespecially the phlogiston adhering to it, and then the peculiar _acid of\nsugar_ crystallizes. Thus with three parts of sugar, and thirty of\nnitrous acid, one part of the proper acid of sugar may be obtained. By\nthe same process an acid may be procured from camphor.\n\nThe _bark of oak_, and some other vegetable substances, especially\nnut-galls, contain a substance which has obtained the name of _the\nastringent principle_; the peculiar property of which is, that it\nprecipitates solutions of iron in the form of a black powder, and in\nthis manner _ink_ is made. But by solution in water and evaporation,\ncrystals, which are a proper _acid of galls_, may be obtained.\n\n_Amber_ is a hard semitransparent substance, chiefly found in Prussia,\neither dug out of the earth, or thrown up by the sea. It is chiefly\nremarkable for its electrical property; but by distillation in close\nvessels there sublimes from it a concreted acid, soluble in 24 times\nits weight of cold water. Amber seems to be of vegetable origin, and to\nconsist of an oil united to this peculiar acid.\n\nThe acids I shall mention next are of a mineral origin; but being of a\nless perfect nature as acids, I shall only just note them here.\n\n_Borax_ is a substance chiefly found in a crystallized state in some\nlakes in the East Indies. It consists of the mineral alkali and a\npeculiar acid, which may be separated, and exhibited in white flakes, by\nputting acid of vitriol to a solution of it in water. This acid has been\ncalled _sedative salt_, from its supposed uses in medicine. It is an\nacid that requires fifty times its weight of water to dissolve it.\n\nSeveral other mineral substances, as _arsenic_, _molybdena_, _tungsten_,\nand _wolfram_, in consequence of being treated as the preceding\nvegetables ones, have been lately found to yield peculiar acids. They\nare also produced in a concrete state, and require a considerable\nproportion of water to make them liquid; but as the water in which they\nare dissolved turns the juice of litmus red, and as they also unite\nwith alkalis, they have all the necessary characteristics of acids.\n\n\n\n\nLECTURE XV.\n\n\n_Of the Phosphoric Acid._\n\nThe most important acid of _animal_ origin, though it has lately been\nfound in some mineral substances, is the _phosphoric_.\n\nPhosphorus itself is a remarkable substance, much resembling sulphur,\nbut much more inflammable. It has been procured chiefly, till of late,\nfrom urine, but now more generally from _bones_, by means of the\nvitriolic acid, which unites with the calcareous earth of which bones\nconsist, and sets at liberty the phosphoric acid, or the base of that\nacid, with which it was naturally combined. The acid thus procured,\nmixed with charcoal, and exposed to a strong heat, makes phosphorus.\n\nThis substance burns with a lambent flame in the common temperature of\nour atmosphere, but with a strong and vivid flame if it be exposed to\nthe open air when moderately warm. In burning it unites with the\ndephlogisticated air of the atmosphere, and in this manner the purest\nphosphoric acid is produced.\n\nThis acid is also procured in great purity by means of the nitrous or\nvitriolic acids, especially the former, which readily combines with the\nphlogiston of the phosphorus, and thus leaves the acid pure. In this\nprocess phlogisticated air is produced.\n\nThis acid is perfectly colourless, and when exposed to heat loses all\nits water, and becomes a glassy substance, not liable to be dissipated\nby fire, and readily uniting with earths.\n\nUnited to the mineral alkali, it forms a neutral salt, lately introduced\ninto medicine. United to the mineral and vegetable alkalis naturally\ncontained in urine, it has obtained the name of _microcosmic salt_,\nfrequently used as a flux for mineral substances with a blow-pipe.\n\nBesides the phosphoric, there are other acids of an animal origin; as\nthat of _milk_, that of _sugar of milk_, that of the _animal calculus_,\nand that of _fat_.\n\nThe acid of milk is the sour whey contained in butter-milk, which, by a\ntedious chemical process, may be obtained pure from any foreign\nsubstance.\n\nThe sugar of milk is procured by evaporating the whey to dryness, then\ndissolving it in water, clarifying it with whites of eggs, and\nevaporating it to the consistence of honey. In this state white crystals\nof the acid of sugar of milk will be obtained.\n\nBy distilling these crystals with nitrous acid, other crystals of the\nproper _acid of sugar of milk_ will be obtained, similar to those of the\nacid of sugar.\n\nIf the human calculus be distilled, it yields a volatile alkali, and\nsomething sublimes from it which has a sourish taste, and therefore\ncalled the _acid of the calculus_. It is probably some modification of\nthe phosphoric acid.\n\nAnimal fat yields an acid by distillation, or by first combining it with\nquick-lime, and then separating it by the vitriolic acid. Siliceous\nearth is corroded by this acid.\n\n\n\n\nLECTURE XVI.\n\n\n_Of Alkalis._\n\nThe class of substances that seems particularly formed by nature to\nunite with acids, and thereby form _neutral salts_, are the _alkalis_.\nThey have all a peculiar acrid taste, not easily defined. They change\nthe blue juices of vegetables green, or purple, and in common with acids\nhave an affinity with water, so as to be capable of being exhibited in a\nliquid form; though when this water is expelled by heat, some of them\nwill assume a solid form.\n\nAlkalis are of two kinds; the _fixed_, which have no smell, and the\n_volatile_ which have a pungent one.\n\nThe fixed alkalis are of _vegetable_ or _mineral_ origin. When in a\nsolid form, they both melt with a moderate heat, and uniting with earthy\nsubstances, make _glass_. With an intense heat they are volatilized.\n\nVegetable alkali is procured by burning plants, and lixiviating the\nashes; a purer kind by the burning of tartar, hence called _salt of\ntartar_; but the purest of all is got by the deflagration of nitre; the\ncharcoal uniting with the acid as it assumes the form of\ndephlogisticated air, and the alkali being left behind.\n\nMineral alkali is found in ashes of sea-weed. It is likewise the basis\nof sea-salt; from which it is separated by several processes, but\nespecially by the calx of lead, which has a stronger affinity with the\nmarine acid with which it is found combined.\n\nAlkalis united with fixed air are said to be _mild_, and when deprived\nof it _caustic_, from their readiness to unite with, and thereby\n_corrode_, vegetable and animal substances. To render them caustic, they\nare deprived of their fixed air by quick-lime; and in this state they\nunite with oils, and make _soap_.\n\nAlkalis have a stronger affinity with acids than metals have with them;\nso that they will precipitate them from their solutions in acid\nmenstruums.\n\nThe vegetable fixed alkali has a strong attraction to water, with which\nit will become saturated in the common state of our atmosphere, when it\nis said to _deliquesce_; and having the appearance of _oil_, the salt of\ntartar is thus said to become _oil of tartar per deliquium_. On the\nother hand, the mineral, or fossil alkali, is apt to lose its water in a\ndry atmosphere, and then it is said to _effloresce_. In this state it is\noften found on old walls.\n\nVolatile alkali is procured by burning animal substances; in Egypt (from\nwhence, as contained in _sal ammoniac_, we till of late imported it)\nfrom camel's dung; but now from bones, by distillation. To the liquor\nthus procured they add vitriolic acid, or substances which contain it.\nThis acid unites with the alkali, and common salt being put to it, a\ndouble affinity takes place. The vitriolic acid uniting with the mineral\nalkali of the salt, makes _Glauber salt_, and the marine acid uniting\nwith the volatile alkali, makes _sal ammoniac_. Slaked lime added to\nthis, unites with the marine acid of the ammoniac, and sets loose the\nvolatile alkali in the form of _alkaline air_, which combining with\nwater, makes the liquid caustic volatile alkali. If chalk (containing\ncalcareous earth united with fixed air) be mixed with the sal ammoniac,\nheat will make the calcareous earth unite with the marine acid, while\nthe fixed air of the chalk will unite with the volatile alkali, and\nassume a solid form, being the _sal volatile_ of the apothecaries.\n\n\n\n\nLECTURE XVII.\n\n\n_Of Liquid Inflammable Substances._\n\nOf liquid inflammable substances the principal is _spirit of wine_,\nsometimes called _ardent spirit_, and, when highly rectified, _alcohol_.\nIt is obtained from vegetable substances by their going through the\nvinous fermentation. It is considerably lighter than water, colourless,\nand transparent, has a peculiar smell and taste, and the property of\ninebriating.\n\nArdent spirit seems to consist of a peculiar combination of phlogiston\nand water; for when the vapour of it is made to pass through a red-hot\nearthen tube, it is resolved into water and inflammable air. It is\nhighly inflammable, and burns without smoke, or leaving any residuum;\nand in the act of burning its phlogiston so unites with dephlogisticated\nair as to make fixed air.\n\nArdent spirit mixes readily with water in all proportions, and also with\nessential oils, and balsams or resins, which are the same thing\ninspissated.\n\nBy its affinity with essential oils, ardent spirit extracts them froth\naromatic plants; and these liquors have obtained the name of\n_tinctures_.\n\nWhen the tinctures are distilled, the more volatile parts of the\nessential oils, which come over in distillation, have acquired the name\nof _waters_; as _Lavender water_, _Rosemary water_, &c. and what remains\nin the still is called the _extract_ of the plant. If the tinctures be\ndiluted with much water, the resinous part of the plant will be obtained\npure, and separated from the extractive part, which will remain\ndissolved in the water, while the resin separates from it.\n\nSpirit of wine will not dissolve the gummy parts of vegetables; and by\nthis means the gummy substances may be separated from their solutions in\nwater, the spirit uniting with the water only. On the other hand, if\nresins be dissolved in spirit of wine, the affusion of water will\nseparate them. By means of the affinity of spirit of wine with water, it\nwill seize upon the water in which several salts are dissolved, and thus\nproduce an instant crystallization of them.\n\nSalt of tartar has a greater affinity to water than spirit of wine, and\nby extracting water from it, will assist in concentrating it; but the\nbest method of rendering spirit wine free from water is distillation,\nthe ardent spirit rising before the water.\n\nSpirit of wine mixed with the vitriolic and other mineral acids, renders\nthem milder, and thereby more proper for certain medicinal uses. This is\ncalled _dulcifying_ them.\n\nSpirit of wine is a powerful antiseptic, and is therefore of use to\npreserve vegetable and animal substances from putrefaction.\n\n\n_Of AEther._\n\nIf spirit of wine be distilled with almost any of the acids, the produce\nis a liquor which has obtained the name of _AEther_, from its extreme\nlightness and volatility, being much lighter, and more volatile, than\nany other fluid that we are acquainted with. It is highly inflammable,\nbut the burning of it is accompanied with smoke, and some soot; and on\nthis account it is a medium between spirit of wine and oil, the acid\nhaving taken from the spirit of wine part of the water that was\nessential to it, at the same time that it communicated something of its\nacid peculiarly modified; since aethers have different properties\naccording to the acids by which they are made; as the _vitriolic_, the\n_nitrous_, the _marine_, and the _acetous_. No aether, however, can be\nmade from the marine acid till it has been in some measure\ndephlogisticated; from which it may be inferred, that dephlogisticated\nair is necessary to the composition of aether. Vitriolic aether is the\nmost common, in consequence of the process by which it is made being the\neasiest.\n\nAEther does not mix with water in all proportions, like spirit of wine,\nbut ten parts of water will take up one of aether. It easily mixes with\nall oils.\n\nIt is something remarkable, that though aether will not dissolve gold, it\nwill take from aqua regia the gold that has been previously dissolved in\nit.\n\nBy the quick evaporation of aether a considerable degree of cold may be\nprocured; and on this principle it has sometimes been applied to relieve\nthe head-ach and other pains.\n\n\n\n\nLECTURE XVIII.\n\n\n_Of Oil._\n\nOil is a liquid inflammable substance, of great tenacity, disposed to\npour in a stream rather than in drops. It is little, if at all, soluble\nin water. It burns with smoke and soot, and leaves a residuum of a coaly\nsubstance. It consists of acid and water combined with phlogiston.\n\nAll oil is the produce of the vegetable or animal kingdom, no proper\nmineral substance containing any of it.\n\nBy distillation oil is in part decomposed, and by this means the thicker\nkinds of oil are rendered thinner and more volatile, the acid, to which\ntheir consistence is chiefly owing, being lost in the process. By\nrepeated distillation it is supposed that all oils may be brought almost\nto the state of aether, and even of ardent spirit.\n\nAcids act powerfully upon oils, but very differently, according to the\nnature of each. Alkalies also combine with oils, and the less thin and\nvolatile they are, the more easily are they soluble in alkalies. The\nunion of alkali and oil makes _soap_. All oil dissolves sulphur, and\nwith it makes what is called a _balsam_. Oils also dissolve metallic\nsubstances, but most sensibly copper and lead. United with the calx of\nlead, it is used in painting.\n\nOil not readily mixing with water, it will diffuse itself over its\nsurface, and, notwithstanding its tenacity, it will do this very\nrapidly, and to a great extent; and then it has the extraordinary\neffect of preventing the action of the wind upon the water, so as to\nprevent the forming of waves. If a quantity of oil and water be put into\na glass vessel and swung, the surface of the water below the oil will be\nseen to change with respect to the vessel, but not that of the oil. If\nspirit of wine be put upon them, that will be at rest, and both the\nlower fluids in motion.\n\nVegetable oil is of two kinds, the _soft_, or _mild_, which has little\nor no taste or smell, and the _essential_ oil, which is thin, and\nretains the smell and taste of the plant from which it was extracted.\n\nMild or sweet oil is expressed from the grains or kernels of vegetables,\nand requires a considerable degree of heat to convert it into vapour, in\nwhich state alone it is capable of being inflamed.\n\n_Essential oil_ is volatile in the heat of boiling water, and is\ngenerally obtained by means of distillation from the most odoriferous\nsorts of plants; but is sometimes found in their vesicles, as in the\nrind of an orange. The strong taste of this kind of oil arises from the\ndisengaged acid which abounds in it; and by this means it is soluble in\nspirit of wine, which sweet oil is not; but it loses much of this\nproperty by repeated distillations. By long exposure to the air it loses\nits more volatile parts, and thereby approaches to the nature of a\nresin. This volatile odoriferous principle has been called the _spiritus\nrector_ of the plant.\n\nThe essential oils of different plants differ much in their specific\ngravity, and also in the manner by which they are affected by cold, some\nbeing heavier and others lighter than water, and some being more\ndifficultly, and others more easily, congealed. Though the differences\nwith respect to _weight_ and _consistency_ in these oils is probably\nowing to the state of the acid that is combined with them, these two\nproperties are wholly independent of each other; some essential oils\nbeing very thin and yet heavy, and others thick and yet light. Essential\noils are used in perfumes, and also in medicine, acting powerfully the\nnervous system.\n\nEssential oils are very apt to be adulterated. If it be with sweet oil,\nit may be discovered by evaporation on white paper, or by a solution in\nspirit of wine, which will not act upon the sweet oil. If spirit of wine\nbe mixed with it, it will be discovered by a milky appearance upon\nputting water to it, which uniting with the spirit, will leave the oil\nmuch divided. If oil of turpentine, which is the cheapest of essential\noils, be mixed with any of the more valuable kinds, it will be\ndiscovered by evaporation; a strong smell of turpentine being left on\nthe paper, or cloth, upon which the evaporation was made.\n\nAnimal oil, like the vegetable, is of two kinds; the first _butter_, or\n_fat_, which is easily congealed, owing to the quantity of acid that is\nintimately combined with it. It resembles the sweet oil of vegetables in\nhaving no smell or taste. The other kind of animal oil is extracted by\ndistillation from the flesh, the tendons, the bones, and horns, &c. of\nanimals. It differs essentially from the other kind of animal oil, by\ncontaining an alkali instead of an acid. By repeated distillation it\nbecomes highly attenuated and volatile; and in this state it is called\nthe _oil of Dippel_, the discoverer of it.\n\nAll oil exposed to much heat is in part decomposed, and acquires a\ndisagreeable smell; and in this state it is said to be _empyreumatic_:\nbut this property is lost by repeated distillations.\n\nBesides the vegetable and animal oils above described, there is a fossil\noil called _bitumen_, the several kinds of which differ much in colour\nand consistence; the most liquid is called _petroleum_, from being found\nin the cavities of rocks, and the more solid kinds are _amber_, _jet_,\n_asphaltum_, and _pit-coal_. When distilled, the principal component\nparts of all these substances are an oil and an acid. But all fossil oil\nis probably of vegetable or animal origin, from masses of vegetables or\nanimals long buried in the earth. Their differences from resins and\nother oily matters are probably owing to _time_; the combinations of\nmineral acids and oils so nearly resembling bitumens, the principal\ndifference being their insolubility in spirit of wine.\n\nThat the most solid of these, as amber, has been formerly in a liquid\nstate, is evident, from insects and other substances being frequently\nfound in them; and pit-coal has been often found with both the internal\ntexture and external appearance of wood; so that strata of pit-coal have\nprobably been beds of peat in some former state of the earth.\n\n\n\n\nLECTURE XIX.\n\n\n_Of Solid Substances._\n\nAll solid substances are capable of becoming fluid by heat, and most of\nthem may thereby be reduced into a state of vapour, or air; and in\npassing from a fluid into a solid state their component parts assume a\nparticular mode of arrangement, called _crystallization_, which differs\naccording to the nature of the substance; so that all solids, especially\nif they be suffered to concrete slowly, may be called _crystals_.\n\nExclusive of _salts_, which have been considered already, as formed by\nthe union of acids and alkalis, solids in general have obtained the\nnames of _earths_, or _stones_, which differ only in their texture; and\nthey are distinguished into those that are _metallizable_, or those that\nare not; the former being called _ores_, and the latter simply _earths_;\nthe principal of which are the _calcareous_, _siliceous_,\n_argillaceous_, _magnesia_, _terra ponderosa_, and a few others which\nhave been discovered lately, but have not been much examined.\n\n\n_Of Calcareous Earth._\n\nCalcareous earth is found in the shells of fishes, the bones of animals,\nchalk, lime-stone, marble, and gypsum: but all calcareous earth is\nsupposed to be of animal origin; and beds of chalk, lime-stone, or\nmarble, are thought to have been beds of shells formed in the sea, in\nsome pristine state of the earth.\n\nThe calcareous earth which is found in shells, lime-stone, and marble,\nis combined with fixed air, discovered by effervescing with acids. To\nobtain it perfectly pure, the earth must be pounded and washed with\nwater, in order to free it from any saline substance which may be\ncontained in it, then dissolved in distilled vinegar, and precipitated\nby mild alkalies. Lime-stone exposed to heat loses about half its\nweight, in fixed air and water, and the remainder, called _quick-lime_,\nattracts water very powerfully, and their union is attended with much\nheat, after which it dissolves into a fine powder called _slaked lime_.\nIf it be left exposed to the atmosphere, it will of itself, by gradually\nimbibing moisture, fall into the state of powder.\n\nWater dissolves about one seven hundredth part of its weight of\nquick-lime, and is then called _lime-water_. Exposed to the air, a crust\nwill be formed on its surface, which is found to consist of calcareous\nearth and fixed air.\n\nLime and water mixed with sand make _mortar_, by which means different\nstones may be made to cohere as one mass, which is the most valuable\nuse of this kind of earth.\n\nCalcareous earth, united with vitriolic acid, makes _gypsum_; and this\nsubstance pounded and exposed to heat, parts with its water, and is then\ncalled _plaister of Paris_. In this state, by imbibing water again, it\nbecomes a firm substance, and thus is useful in making moulds, &c.\n\nThe earth of animal bones is calcareous united to the phosphoric acid.\n\n\n_Of Siliceous Earth._\n\nSiliceous earth seems to be formed by nature from chalk, perhaps by the\nintroduction of some unknown acid, which the vitriolic acid is not able\nto dislodge. It abounds in most substances which are hard enough to\nstrike fire with steel, as _flint_, _rock crystal_, and most _precious\nstones_. It is not acted upon by any acid except the fluor and\nphosphoric, but especially the former: but it is soluble in alkalies;\nand being then dissolved in water, makes _liquor silicum_, from which\nthe purest siliceous earth may be precipitated by acids. For this\npurpose about four times the weight of alkali must be made use of. With\nabout equal weights of alkali and siliceous sand is made _glass_, of so\ngreat use in admitting light and excluding the weather from our houses,\nas well as for making various useful utensils. To make glass perfectly\ncolourless, and at the same time more dense, commonly called _flint\nglass_, manufacturers use a certain proportion of calx of lead and\nmanganese.\n\nSiliceous earth is not affected by the strongest heat, except by means\nof a burning lens, or dephlogisticated air.\n\n\n\n\nLECTURE XX.\n\n\n_Of Argillaceous Earth._\n\nArgillaceous earth is found in _clay_, _schistus_, or _slate_, and in\n_mica_; but the purest is that which is precipitated from a solution of\nalum by alkalies; for alum consists of the union of vitriolic acid and\nargillaceous earth.\n\nThis species of earth is ductile with water; it then hardens and\ncontracts by heat, so as to be of the greatest use in forming _bricks_,\nor stones of any required form or size. By means of the property of clay\nto contract in the fire, Mr. Wedgwood has constructed an excellent\nthermometer to measure the degrees of extreme heat.\n\nThe ductility of clay seems to depend upon some acid, probably the\nvitriolic, adhering to it; for it loses that property when it is burned\ninto a brick, but recovers it when it has been again dissolved in an\nacid.\n\n\n_Of Terra Ponderosa._\n\n_Terra ponderosa_, or _marmor metallicum_, is generally found in two\nstates, viz. united to vitriolic acid, when it is called _calk_, or to\nfixed air, when it is called _terra ponderosa aerata_.\n\nTo obtain it pure from its union with the vitriolic acid, it must be\nmelted with about twice its weight of fixed alkali; which unites with\nthe acid, and forming a saline substance, may be washed out of it. In\nthis state it contains water, and therefore, when exposed to heat, will\nyield fixed air; whereas the terra ponderosa aerata will not yield fixed\nair by heat only, but when steam is made to pass over it when red hot.\nThis proves that water is essential to the composition of fixed air.\n\nThis stone is distinguishable by its great specific gravity, being four\ntimes as heavy as water; but though in this it resembles an _ore_, it\nhas not been found to be metallizable.\n\n\n_Of Magnesia._\n\nThis species of earth is found in _steatites_, or _soap rock_, _Spanish\nchalk_, _asbestus_, and _Muscovy talck_; but the purest is got by\ndissolving _Epsom salts_ (which consists of this earth united to the\nvitriolic acid) and precipitating it by a mild alkali. In this state it\nbecomes united to fixed air, which may be expelled by heat. It is then\n_calcined_, or _caustic_, but differs from quick-lime by not being\nsoluble in water.\n\n_Asbestus_, which contains much of this kind of earth, is remarkable for\nnot being destructible by heat, though it is sometimes found in flexible\nfibres, so as to be capable of being woven into cloth.\n\n_Muscovy talck_ is remarkable for the thin and transparent flakes into\nwhich it is divisible, and thereby capable of various uses.\n\nThere are some other distinct species of earth, particularly one brought\nfrom Botany Bay, and another called _Stontiate_, from the place where it\nwas found in Scotland; but they have not as yet been much examined.\n\nAll stones formed by nature are compounded, and to distinguish them from\none another, and ascertain the parts of which they consist, is the\nsubject of _lithology_, a very extensive branch of knowledge.\n\nAll the simple earths are nearly, if not absolutely, _infusible_; but\nwhen they are mixed they may all be fused.\n\n\n\n\nLECTURE XXI.\n\n\n_Of Ores_.\n\nMetallizable earths, commonly called _ores_, when united to phlogiston,\nmake the metals, distinguishable for their specific gravity, their\nopacity, shining appearance, and fusibility.\n\nAll the proper metals are _malleable_, and those which are not so are\ncalled _semi-metals_.\n\nThe metals again are subdivided into the _perfect_ and _imperfect_. The\nformer, which are _gold_, _silver_, and _platina_, suffer no change by\nfusion, or the longest continued heat: whereas heat calcines or\ndissipates the phlogiston of the imperfect metals, which are _mercury_,\n_lead_, _copper_, _iron_, and _tin_, so that they return to the state of\nearth; and this earth is always heavier than the metal, though of less\nspecific gravity, having received an addition of weight from water or\nair: but these earths, or ores, being exposed to heat in contact with\nsubstances containing phlogiston, again become metals, and are then said\nto be _revived_.\n\nThe semi-metals are _bismuth_, _zinc_, _nickel_, regulus of _arsenic_,\nof _cobalt_, of _antimony_, of _manganese_, of _wolfram_, and of\n_molybdena_.\n\nAll metallic substances are crystallizable, and each in a peculiar form,\nwhich is discovered by leaving a hole in the bottom of the crucible in\nwhich they are melted, and drawing out the stopper, when the mass is\nbeginning to lose its fluidity.\n\nSome of the metals will not unite to others when hot, and others of them\nwill; and such as will unite with others are called _solders_. Thus tin\nis a solder for lead, and brass, gold, or silver, for iron.\n\nOres are never found in regular strata, like the different kinds of\nearth; but in places which have formerly been cavities, running in all\ndirections, with respect to the regular strata, and commonly called\n_veins_.\n\nMany of the ores in their natural state are said to be _mineralized_\nwith arsenic or sulphur, those substances being intimately united with\nthe metallic earths.\n\nIn order to convert the ores into metals, some of them are first reduced\nto powder, to wash out the earthy or saline particles. They are then\nkept in a red heat, which the workmen call _roasting_, in order to drive\naway the arsenic, or sulphur, which are volatile; and in the last place\nthey are fused in contact with charcoal, or other substances containing\nphlogiston; and to promote the fusion, lime-stone is frequently mixed\nwith them. When the operation is completed, the unmetallic parts are\nconverted into glass, or _scoria_, which lies on the surface, whereas\nthe metal is found at the bottom.\n\nTo discover the quantity of metal in a small piece of ore is called\n_assaying_.\n\nWhen metals are fused together, the specific gravity, fusibility, and\nother properties are changed, and in such a manner as could not be\ndiscovered from the properties of the constituent parts.\n\n\n_Of Gold._\n\nGold is the heaviest of all metallic bodies except platina. It appears\nyellow or reddish by reflected light, but green or blue by transmitted\nlight, when it is reduced to thin plates.\n\nThough gold undergoes no change in a common furnace, or burning lens, it\nmay, in part, at least, be calcined by the electric shock.\n\nGold has the greatest _ductility_, and in wires of equal diameters, it\nhas the greatest _tenacity_, of all the metals. One grain of it may be\nmade to cover 56 square inches; some gold leaf being less than a\n200,000th part of an inch thick; and when it is made to cover a silver\nwire, the gold upon it may not be more than one twelfth part of the\nthickness of the gold leaf.\n\nThis metal is soluble in aqua regia; and being precipitated by a\nvolatile alkali, makes a powder called _aurum fulminans_, which is one\nfourth heavier than the gold, and explodes with great violence in a heat\nsomething greater than that of boiling water.\n\nTin precipitates gold in the form of a purple powder, called the _powder\nof Cassius_, from the inventor of it, and is used in enamels, or the\nglassy coating which is given to metals by heat.\n\nGold unites with most of the metals, especially with mercury, and these\nmixtures are called _amalgams_. In gilding, the amalgam is applied to\nthe surface of the metal to be gilded, and the mercury is driven off by\nheat, leaving the gold attached to the surface.\n\nGold mixed with iron, makes it harder, for the purpose of cutting\ninstruments.\n\nTo separate gold from the imperfect metals, such as copper, &c. it is\nmixed with lead, and then exposed to a strong heat, which calcines the\nlead, and with it the imperfect metals, leaving the gold pure. This\nprocess is called _cupellation_, from being performed in a small\ncrucible called a _cupell_. When the gold is mixed with silver, three\nparts more of silver are put to it, and then the silver is dissolved by\nnitrous acid, leaving the gold pure. This process is called\n_quartation_, from the gold being one fourth part of the mass.\n\nThe fineness of gold is generally estimated by dividing the gold into\ntwenty-four parts, called _carats_. The phrase twenty-three carats fine\nmeans that the mass contains twenty-three parts out of twenty-four of\npure gold, the remainder being _alloy_, of some baser metal. The\nfineness of gold may in some measure be discovered by the colour it\nleaves upon a _touch-stone_, or fine-grained basaltes.\n\nGold is generally found nearly pure, but mixed with earth, or diffused\nin fine grains through stones.\n\n\n\n\nLECTURE XXII.\n\n\n_Of Silver._\n\nSilver is the whitest of all the metals, very ductile, but less so than\ngold; the thinnest leaves of it being one third thicker than those of\ngold. It is not calcined in the heat of a common furnace, but partially\nso by repeated fusion, or a strong burning lens.\n\nSulphureous fumes unite with silver, and tinge it black. The nitrous\nacid dissolves it, and will hold more than half its weight of it in\nsolution. When fully saturated, this solution deposits crystals, which\nare called _lunar nitre_, or _nitre of silver_. When these crystals are\nmelted, and the water they contain driven off, a black substance,\ncalled _lapis infernalis_, or _lunar caustic_, is formed. This is used\nas a cautery in surgery. A strong heat will decompose this lunar nitre,\nand recover the silver.\n\nThough the nitrous acid dissolves silver the most readily, the marine\nacid will deprive the nitrous of it, and form a substance called _luna\ncornea_, because, when it is melted and cold, it becomes a transparent\nmass something resembling _horn_. From this luna cornea the purest\nsilver may be obtained. The vitriolic acid will likewise deprive the\nnitrous of the silver contained in it, and form a white powder, not\neasily soluble in water.\n\nA fulminating silver may be made by the following process: the silver\nmust first be dissolved in pale nitrous acid, then precipitated by\nlime-water, dried, and exposed to the air three days. It must then be\nwashed in caustic volatile alkali, after which the fluid must be\ndecanted, and the black powder left to dry in the air. The slightest\nfriction will cause this powder to fulminate. It is said, that even a\ndrop of water falling upon it will produce this effect; so that it\nought to be made only in very small quantities, and managed with the\ngreatest caution.\n\nMost of the metals precipitate silver. That by mercury may be made to\nassume the form of a tree, called _arbor Dianae_.\n\nSilver is found native in Peru; and the ores frequently contain sulphur,\nor arsenic, or both.\n\n\n_Of Platina._\n\nPlatina is a metal lately discovered in the gold mines of Mexico, where\nit is found in small particles, never exceeding the size of a pea, mixed\nwith ferruginous sand and quartz.\n\nThe strongest fire will not melt these grains, though it will make them\ncohere; but they may be melted by a burning lens, or a blow-pipe\nsupplied with dephlogisticated air.\n\nPure platina is the heaviest body in nature, its specific gravity\nexceeding twenty-two. It is very malleable, though considerably harder\nthan gold or silver, and has the property of welding in common with\niron. This metal is not affected by exposure to the air, or by any\nsimple acid, though concentrated and hot; but it is dissolved by\ndephlogisticated marine acid, and by aqua regia, in which a little\nnitrous air is procured. The solution is brown, and when diluted yellow.\nThis liquor is very corrosive, and tinges animal substances of a\nblackish brown colour. Platina is precipitated from a solution in aqua\nregia by sal-ammoniac, as gold is by martial vitriol. Iron is\nprecipitated from this solution by the Prussian alkali. Also most of the\nmetals precipitate platina, but not in its metallic state.\n\nArsenic facilitates the solution of platina; and by melting it with\nequal parts of arsenic and vegetable alkali, and then reducing the mass\nto a powder, it may be made to take any form; and a strong heat will\ndissipate the arsenic and the alkali, leaving the platina in the shape\nrequired, not fusible by any heat in a common furnace.\n\nPlatina does not readily combine with gold or silver, and it resists the\naction of mercury as much as iron; but it mixes well with lead, making\nit less ductile, and even brittle, according to the proportion of the\nplatina. With copper it forms a compound which takes a beautiful polish,\nnot liable to tarnish, and is therefore used with advantage for mirrors\nof reflecting telescopes. It unites easily with tin, and also with\nbismuth, antimony, and zinc.\n\n\n\n\nLECTURE XXIII.\n\n\n_Of Mercury._\n\nMercury is the most fusible of all the metals, not becoming solid but in\n40 deg. below 0 in Fahrenheit's thermometer. It is then malleable. It is\nheavier than any other metal except gold or platina. It is volatile in a\ntemperature much lower than that of boiling water, and in vacuo in the\ncommon temperature of the atmosphere; and at six hundred it boils.\n\nIn a degree of heat in which it would rise easily in vapour, mercury\nimbibes pure air, and becomes a red calx, called _precipitate per se_.\nAt a greater degree of heat it parts with that air, and is running\nmercury again.\n\nMercury is not perceptibly altered by exposure to the air.\n\nMercury is acted upon by the vitriolic acid when hot. In this process\nvitriolic acid air is procured, and the mercury is converted into a\nwhite substance, which being dipped in water becomes yellow, called\n_turbith mineral_, one third heavier than the mercury from which it was\nmade. By heat this substance parts with its pure air, and becomes\nrunning mercury; but if the process be made in a clean earthen vessel,\nthere will remain a portion of _red calx_, which cannot be reduced by\nany degree of heat, except in contact with some substance containing\nphlogiston. If this be done with a burning lens, in inflammable air,\nmuch of the air will be absorbed.\n\nMercury is dissolved most readily in the nitrous acid, when the purest\nnitrous air is procured; and there remains a substance which is first\nyellow, and by continuance red, called _red precipitate_. In a greater\ndegree of heat the dephlogisticated air will be recovered, and the\nmercury be revived; but the substance yields nitrous air after it\nbecomes solid, and till it changes from yellow to red.\n\nThe precipitates of mercury from acids by means of alkalies possess the\nproperty of exploding, when they are exposed to a gradual heat in an\niron spoon, after having been triturated with one sixth of their weight\nof the flowers of sulphur. The residuum consists of a violet-coloured\npowder, which, by sublimation, is converted into cinnabar.\n\nIt seems, therefore, as if the sulphur combined suddenly with the\nmercury, and expelled the dephlogisticated air in an elastic state.\n\nThe marine acid seizes upon mercury dissolved in nitrous acid, and if\nthe acid be dephlogisticated, the precipitate is _corrosive sublimate_;\nbut with common marine acid, it is called _calomel_, or _mercurius\ndulcis_. This preparation is generally made in the dry way, by\ntriturating equal parts of mercury, common salt and vitriol, and\nexposing the whole to a moderate heat; when the corrosive sublimate\nrises, and adheres to the upper part of the glass vessel in which the\nprocess is made.\n\nMercury combines readily with sulphur by trituration, and with it forms\na black powder called _Ethiops mineral_. A more intimate combination of\nmercury and sulphur is made by means of fire. This is called _cinnabar_,\nabout one third of which is sulphur. Vermillion is cinnabar reduced to\npowder.\n\nMercury readily unites with oil, and with it forms a deep black or blue\ncompound, used in medicine.\n\nIt readily combines with most of the metals, and when it is used in a\nsufficient quantity to make them soft, the mixture is called an\n_amalgam_. It combines most readily with gold, silver, lead, tin,\nbismuth, and zinc. Looking-glasses are covered on the back with an\namalgam of mercury and tin.\n\nWhen mercury is united with lead or other metals, it is rendered less\nbrilliant and less fluid; but agitation in pure air converts the impure\nmetal into a calx, together with much of the mercury, in the form of a\nblack powder.\n\nHeat recovers the pure air, and the mercury, leaving the calx of the\nimpure metal.\n\nMuch mercury is found native in a slaty kind of earth, or in masses of\nclay or stone; but the greatest quantity is found combined with sulphur\nin _native cinnabar_.\n\n\n\n\nLECTURE XXIV.\n\n\n_Of Lead._\n\nLead is a metal of a bluish tinge, of no great tenacity, but very\nconsiderable specific gravity, being heavier than silver. It melts long\nbefore it is red hot, and is then calcined, if it be in contact with\nrespirable air. When boiling it emits fumes, and calcines very rapidly.\nIt may be granulated by being poured into a wooden box, and agitated.\nDuring congelation it is brittle, so that the parts will separate by the\nstroke of a hammer; and by this means the form of its crystals may be\ndiscovered.\n\nIn the progress of calcination it first becomes a dusky grey powder,\nthen yellow, when it is called _massicot_; then, by imbibing pure air,\nit becomes red, and is called _minium_, or _red lead_. In a greater\ndegree of heat it becomes massicot again, having parted with its pure\nair. If the heat be too great, and applied rapidly, it becomes a flaky\nsubstance, called _litharge_; and with more heat it becomes a _glass_,\nwhich readily unites with metallic calces and earths, and is a principal\ningredient in the manufacture of _flint glass_, giving it its peculiar\ndensity and refractive power.\n\nThough lead soon tarnishes, the imperfect calx thus made does not\nseparate from the rest of the metal, and therefore protects it from any\nfarther action of the air, by which means it is very useful for the\ncovering of houses, and other similar purposes. All acids act upon lead,\nand form with it different saline substances. _White-lead_ consists of\nits union with vinegar and pure air. Also dissolved in vinegar, and\ncrystallized, it becomes _sugar of lead_, which, like all the other\npreparations of this metal, is a deadly poison.\n\nOils dissolve the calces of lead, which, by this means, is the basis of\npaints, plaisters, &c.\n\nBy means of heat litharge decomposes common salt, the lead uniting with\nthe marine acid, and forming a yellow substance, used in painting, and\nby this means the fossil alkali is separated.\n\nLead unites with most metals, though not with iron. Two parts of lead\nand one of tin make a _solder_, which melts with less heat than either\nof the metals separately; but a composition of eight parts of bismuth,\nfive of lead, and three of tin, makes a metal which melts in boiling\nwater.\n\nThis metal will be dissolved by water if it contain any saline matter,\nand the drinking of it occasions a peculiar kind of cholic.\n\nLead is sometimes found native, but generally minerally mineralized with\nsulphur or arsenic, and often mixed with a small quantity of silver.\n\n\n_Of Copper._\n\nCopper is a metal of a reddish or brownish colour, considerably\nsonorous, and very malleable.\n\nAt a heat far below ignition, the surface, of copper becomes covered\nwith a range of prismatic colours, the commencement of its calcination;\nand with more heat a black scale is formed, which easily separates from\nthe metal, and in a strong heat it melts, and burns with a bluish green\nflame.\n\nCopper rusts by exposure to the air; but the partially-calcined surface\nadheres to the metal, as in the case of lead, and thus preserves it from\nfarther corrosion.\n\nCopper dissolved in the vitriolic acid forms crystals of a blot colour,\ncalled _blue copperas_. From this solution it is precipitated by iron,\nwhich by this means becomes coated with copper. The nitrous acid\ndissolves copper with most rapidity, producing nitrous air. If the\nsolution be distilled, almost all the acid will be retained in the\nresiduum, which is white; but more heat will expel the acid, chiefly in\nthe form of dephlogisticated air, and the remainder will be a black\nsubstance, consisting of the pure calx of copper. The vegetable acids\ndissolve copper as well as the mineral ones, which makes the use of this\nmetal for culinary purposes in some cases dangerous. To prevent this\nthey give it a coat of tin. The solution of copper in the vegetable acid\nis called _verdigris_.\n\nAlkalies dissolve copper as well as acids. With the volatile alkali a\nblue liquor is formed, but in some cases it becomes colourless. All the\ncircumstances of this change of colour have not yet been examined. Both\noil and sulphur will dissolve copper, and with the latter it forms a\nblackish grey compound, used by dyers.\n\nCopper readily unites with melted tin, at a temperature much lower than\nthat which is necessary to melt the copper; by which means copper\nvessels are easily covered with a coating of tin. A mixture of copper\nand tin, called _bronze_, the specific gravity of which is greater than\nthat of the medium of the two metals, is used in casting statues,\ncannon, and bells; and in a certain proportion this mixture is excellent\nfor the purpose of mirrors of reflecting telescopes, receiving a fine\npolish, and not being apt to tarnish. Copper and arsenic make a brittle\ncompound called _tombach_; and with zinc it makes the useful compound\ncommonly called _brass_, in which zinc is about one third of its weight.\n\nCopper is sometimes found native; but commonly mixed with sulphur, in\nores of a red, green, or blue colour.\n\nCopper being an earlier discovery than that of iron, was formerly used\nfor weapons and the shoeing of horses; and the ancients had a method,\nwith which we are not well acquainted, of giving it a considerable\ndegree of hardness, so that a sword made of it might have a pretty good\nedge.\n\n\n\n\nLECTURE XXV.\n\n\n_Of Iron._\n\nIron is a metal of a bluish colour, of the greatest hardness, the most\nvariable in its properties, and the most useful of all the metals; so\nthat without it it is hardly possible for any people to make great\nadvances in arts and civilization.\n\nThis metal readily parts with its phlogiston, so as to be very subject\nto calcine, or rust, by exposure to the air. The same is evident by the\ncolours which appear on its surface when exposed to heat, and also when\nit is struck with flint; the particles that fly from it being iron\npartially calcined. In consequence of its readily parting with its\nphlogiston, it is capable of burning, like wood or other fuel, in pure\nair.\n\nIron and platina have the property of _welding_ when very hot, so that\ntwo pieces may be joined without any solder.\n\nWhen iron is heated in contact with steam, part of the water takes the\nplace of the phlogiston, while the rest unites with it, and makes\ninflammable air. By this means the iron acquires one third more weight,\nand becomes what is called _finery cinder_. This substance, heated in\ninflammable air, imbibes it, parts with its water, and becomes perfect\niron again. If the iron be heated in pure air, it also imbibes the\nwater, of which that air chiefly consists, and also a portion of the\npeculiar element of the pure air.\n\nThe solution of iron in spirit of vitriol produces _green copperas_;\nwhich being calcined, becomes a red substance, called _colcothar_.\n\nThe precipitate of iron, by an infusion of galls, is the colouring\nmatter in _ink_, which is kept suspended by means of gum. The\nprecipitate from the same solution by phlogisticated alkali, is\n_Prussian blue_.\n\nWater saturated with fixed air dissolves iron, and makes a pleasant\nchalybeat.\n\nThe calx of iron gives a green colour to glass.\n\nIron readily combines with sulphur. When they are found combined by\nnature, the substance is called _pyrites_.\n\nThe union of phosphoric acid with iron makes it brittle when cold,\ncommonly called _cold short_; and the union of arsenic makes it brittle\nwhen hot, thence called _red short_.\n\nIron unites with gold, silver, and platina, and plunged in a white heat\ninto mercury, it becomes coated with it; and if the process be\nfrequently repeated, it will become brittle, which shews that there is\nsome mutual action between them.\n\nIron readily unites with tin; and by dipping thin plates of iron into\nmelted tin, they get a complete coating of it, and make the _tinned\nplates_ in common use.\n\nWhen crude iron comes from the smelting furnace it is brittle; and when\nit is white within, it is extremely hard; but when it has a black grain,\nowing to its having more phlogiston, it is softer, and may be filed and\nbored.\n\nCast iron becomes _malleable_ by being exposed to a blast of air when\nnearly melting; the consequence of which is a discharge of inflammable\nair, and the separation of a liquid substance, which, when concreted, is\ncalled _finery cinder_. The iron generally loses one fourth of its\nweight in the process. Crude iron contains much _plumbago_, and the\naccess of pure air probably assists in discharging it, by converting it\ninto air, chiefly inflammable.\n\nMalleable iron, exposed to a red heat in contact with charcoal, called\n_cementation_, converts it into _steel_, which has the properties of\nbecoming much harder than iron, and very elastic, by being first made\nvery hot, and then suddenly cooled, by plunging it in cold water. By\nfirst making it very hard, and then giving different degrees of heat,\nand cooling it in those different degrees, it is capable of a great\nvariety of _tempers_, proper for different uses. Of the degrees of heat\nworkmen judge by the change of colour on its surface. Steel, like crude\niron, is capable of being melted without losing its properties. It is\nthen called _cast steel_, and is of a more uniform texture. Iron\nacquires some little weight by being converted into steel; and when\ndissolved in acid, it yields more plumbago. Steel has something less\nspecific gravity than iron. If the cementation be continued too long,\nthe steel acquires a darkish fracture, it is more fusible, and incapable\nof welding. Steel heated in contact with earthy matters, is reduced to\niron.\n\nIron is the only substance capable of _magnetism_; and hardened steel\nalone is capable of retaining magnetism. The loadstone is an ore of\niron.\n\n\n\n\nLECTURE XXVI.\n\n\n_Of Tin._\n\nTin is a metal of a slightly yellowish cast, though harder than lead,\nvery malleable, but of no great tenacity; so that wires cannot be made\nof it. It easily extends under the hammer, and plates of it, called\n_tinfoil_, are made only one thousandth part of an inch thick, and might\nbe made as thin again.\n\nTin has less specific gravity than any other metal. It melts long before\nignition, at 410 of Fahrenheit, and by the continuance of heat is slowly\nconverted into a white powder, which is the chief ingredient in _putty_,\nused in polishing, &c. Like lead, it is brittle when heated little short\nof fusion, and may be reduced into grains by agitation as it passes from\na fluid to a solid state.\n\nThe calx of tin resists fusion more than that of any other metal, which\nmakes it useful in making an opaque white enamel.\n\nTin loses its bright surface when exposed to the air, but is not\nproperly subject to rust; so that it is useful in protecting iron and\nother metals from the effects of the atmosphere.\n\nConcentrated vitriolic acid, assisted by heat, dissolves half its weight\nof tin, and yields vitriolic acid air. With more water it yields\ninflammable air. During the solution the phlogiston of the tin uniting\nwith the acid, forms sulphur, which makes it turbid. By long standing,\nor the addition of water, the calx of tin is precipitated from the\nsolution. The nitrous acid dissolves tin very rapidly without heat, and\nyields but little nitrous air. With marine acid this metal yields\ninflammable air. With aqua regia it assumes the form of a gelatinous\nsubstance used by dyers to heighten the colour of some red tinctures, so\nas to produce a bright scarlet in dying wool.\n\nA transparent liquor, which emits very copious fumes, called, from the\ninventor, _the smoking liquor of Libavius_, is made by distilling equal\nparts of amalgam of tin and mercury with corrosive sublimate, triturated\ntogether. A colourless liquor comes over first, and then a thick white\nfume, which condenses into the transparent liquor above mentioned. Mr.\nAdet has shewn, that this liquor bears the same relation to the common\nsolution of tin, that corrosive sublimate does to calomel, and has given\nan ingenious solution of many of its properties.\n\nTin detonates with nitre; and if the crystals made by the solution of\ncopper in the nitrous acid be inclosed in tinfoil, nitrous fumes will be\nemitted, and the whole will become red hot. Also if five times its\nweight of sulphur be added to melted tin, a black brittle compound,\nwhich readily takes fire, will be formed.\n\nAnother combination of tin, sulphur, and mercury, makes a light yellow\nsubstance called _aurum musivum_ used in painting.\n\nTin is the principal ingredient in the composition of _pewter_, the\nother ingredients being lead, zinc, bismuth, and copper; each pewterer\nhaving his peculiar receipt. It is also used in coating copper and iron\nplates, and in silvering looking-glasses, besides being cast into a\nvariety of forms, when it is called _block tin_.\n\nTin is sometimes found native, but is generally mineralized with sulphur\nand arsenic. The latter is thought to be always contained in tin, and to\nbe the cause of the crackling noise made by bending plates of it.\n\n\n_Of the Semi-metals._\n\nBismuth is a semi-metal of a yellowish or reddish cast, but little\nsubject to change in the air; harder than lead, but easily broken, and\nreducible to powder. When broken it exhibits large shining facets, in a\nvariety of positions. Thin pieces of it are considerably sonorous.\n\nBismuth melts at about 460 deg. of Fahrenheit. With more heat it ignites,\nand burns with a slight blue flame, while a yellowish calx, called\n_flowers of bismuth_, is produced. With more heat it becomes a greenish\nglass. In a strong heat, and in close vessels, this metal sublimes.\n\nVitriolic acid, even concentrated and boiling, has but little effect\nupon bismuth; but the nitrous acid acts upon it with the greatest\nrapidity and violence, producing much nitrous air, mixed with\nphlogisticated nitrous vapour. From the solution of bismuth in this\nacid, a white substance, called _magistery of bismuth_, is precipitated\nby the affusion of water. This has been used as a paint for the skin\nbut has been thought to injure it.\n\nThe marine acid does not readily act upon bismuth; but when\nconcentrated, it forms with it a saline combination, which does not\neasily crystallize, but may be sublimed in the form of a soft fusible\nsalt, called _butter of bismuth_.\n\nBismuth unites with most metallic substances, and in general renders\nthem more fusible. When calcined with the imperfect metals, it unites\nwith them, and has the same effect as lead in cupellation.\n\nBismuth is used in the composition of pewter, in printers' types, and\nother metallic mixtures.\n\nThis metal is sometimes found native, but more commonly mineralized with\nsulphur.\n\n\n\n\nLECTURE XXVII.\n\n\n_Of Nickel._\n\nNickel is a semi-metal of a reddish cast, of great hardness, and always\nmagnetical; on which account it is supposed to contain iron, though\nchemists have not yet been able to separate them.\n\nThe purest nickel was so infusible as not to run into a mass in the\nstrongest heat of a smith's forge; but then it was in some degree\nmalleable.\n\nConcentrated acid of vitriol only corrodes nickel. Alkalies precipitate\nit from its solution in the nitrous acid, and dissolve the precipitate.\nIt readily unites with sulphur.\n\nNickel is found either native or mineralized with several other metals,\nespecially with copper, when it is called _kupfer nickel_, or _false\ncopper_, being of a reddish or copper colour.\n\nThis semi-metal has not yet been applied to any use.\n\n\n_Of Arsenic._\n\nWhat is commonly called _arsenic_ is the calx of a semi-metal called the\n_regulus of arsenic_. It is a white and brittle substance, expelled from\nthe ores of several metals by heat. It is then refined by a second\nsublimation, and melted into the masses in which it is commonly sold.\nThis calx is soluble in about eighty times its weight of cold water, or\nin fifteen times its weight of boiling water. It acts in many respects\nlike an acid, as it decomposes nitre by distillation, when the nitrous\nacid flies off, and the _arsenical salt of Macquer_ remains behind.\n\nWhen the calx of arsenic is distilled with sulphur, the vitriolic acid\nflies off, and a substance of a yellow colour, called _orpiment_, is\nproduced. This appears to consist of sulphur and the regulus of arsenic;\npart of the sulphur receiving pure air from the calx, to which it\ncommunicates phlogiston; and thus the sulphur becomes converted into\nvitriolic acid, while the arsenical calx is reduced, and combines with\nthe rest of the sulphur.\n\nThe combination of sulphur and arsenic, by melting them together, is of\na red colour, known by the name of _realgal_, or _realgar_. It is less\nvolatile than orpiment.\n\nThe solution of fixed alkali dissolves the calx of arsenic, and by means\nof heat a brown tenacious mass is produced, and having also a\ndisagreeable smell, it is called _liver of arsenic_.\n\nThe regulus of arsenic is of a yellow colour, subject to tarnish or grow\nblack, by exposure to the air, very brittle, and of a laminated texture.\nIn close vessels it wholly sublimes, but burns with a small flame in\npure air.\n\nVitriolic acid has little action upon this semi-metal, except when hot;\nbut the nitrous acid acts readily upon it, and likewise dissolves the\ncalx, as does boiling marine acid, though it affects it very little when\ncold.\n\nMost of the metals unite with the regulus of arsenic.\n\nDephlogisticated marine acid converts the calx of arsenic into\n_arsenical acid_ by giving it pure air.\n\nThe acid of arsenic acts more or less upon all metals, but the phenomena\ndo not appear to be of much importance.\n\nThe calx of acid is used in a variety of the arts, especially in the\nmanufactory of glass. Orpiment and realgar are used as pigments. Some\nattempts have been made to introduce it into medicine, but being\ndangerous, the experiments should be made with caution.\n\n\n_Of Cobalt._\n\nCobalt is a semi-metal of a grey or steel colour, of a close-grained\nfracture, more difficult of fusion than copper, not easily calcined. It\nsoon tarnishes in the air, but water has no effect upon it.\n\nCobalt, dissolved in _aqua regia_, makes an excellent sympathetic ink,\nappearing green when held to the fire, and disappearing when cold,\nunless it has been heated too much, when it burns the paper.\n\nThe calx of cobalt is of a deep blue colour, which, when fused, makes\nthe blue glass called _smalt_. The ore of cobalt, called _zaffre_, is\nfound in several parts of Europe, but chiefly in Saxony. As it is\ncommonly sold, it contains twice or thrice its weight of powder of\nflints. The smalt is usually composed of one part of calcined cobalt,\nfused with two parts of powder of flint and one of pot-ash.\n\nThe chief use of cobalt is for making smalt; but the powder and the\nblue-stone used by laundresses is a preparation made by the Dutch of a\ncoarse kind of smalt.\n\n\n_Of Zinc._\n\nZinc is a semi-metal of a bluish cast, brighter than lead, and so far\nmalleable as not to be broken by a hammer, though it cannot be much\nextended. When broken by bending, it appears to consist of cubical\ngrains. If it be heated nearly to melting, it will be sufficiently\nbrittle to be pulverized. It melts long before ignition, and when it is\nred hot, it burns with a dazzling white flame, and is calcined with\nsuch rapidity, that its calx flies up in the form of white flowers,\ncalled _flowers of zinc_, or _philosophical wool_. In a stronger heat\nthey become a clear yellow glass. Heated in close vessels, this metal\nrises without decomposition, being the most volatile of all the metals\nexcept the regulus of _arsenic_.\n\nZinc dissolved in diluted vitriolic acid, yields much inflammable air,\nand has a residuum, which appears to be plumbago, and the liquor forms\ncrystals, called _white copperas_. This metals also yields inflammable\nair when dissolved in the marine acid. Dissolved in the nitrous acid, it\nyields dephlogisticated nitrous air, with very little proper nitrous\nair.\n\nThe ore of zinc, called _calamine_, is generally of a white colour; and\nthe chief use of it is to unite it with copper, with which it makes\nbrass and other gold-coloured mixtures of metals. The calx and the salts\nof this metal are occasionally used in medicine.\n\n\n\n\nLECTURE XXVIII.\n\n\n_Of Antimony._\n\nThe regulus of antimony is of a silvery white colour, of a scaly\ntexture, very brittle, and melts soon after ignition. By continuance of\nheat it calcines in white fumes, called _argentine flowers of antimony_,\nwhich melt into a hyacinthine glass. In close vessels it rises without\ndecomposition. Its calx is soluble in water, like that of arsenic. This\nmetal tarnishes, but does not properly rust, by exposure to the air.\n\nThis metal is soluble in aqua regia. It detonates with nitre, and what\nremains of equal parts of nitre and regulus of antimony after\ndetonation, in a hot crucible, is called _diaphoretic antimony_. The\nwater used in this preparation contains a portion of the calx suspended\nby the alkali, and being precipitated by an acid, is called _ceruse of\nantimony_.\n\nWhen regulus of antimony is pulverized and mixed with twice its weight\nof corrosive sublimate (which is attended with heat) and then distilled\nwith a gentle fire, a thick fluid comes over, which is congealed in the\nreceiver, or in the neck of the retort, and is called _butter of\nantimony_. The residuum consists of revived mercury, with some regulus\nand calx of antimony. When this butter of antimony is thrown into pure\nwater, there is a white precipitate, called _powder of algaroth_, a\nviolent emetic. Nitrous acid dissolves the butter of antimony; and when\nan equal weight of nitrous acid has been three times distilled to\ndryness from butter of antimony, the residuum, after ignition, is called\n_bezoar mineral_, and seems to be little more than a calx of the metal.\n\nCrude antimony, which has been much used in the experiments of\nalchemists, is a combination of sulphur and regulus of antimony. Heat\nmelts it, and finally converts it into glass, of a dark red colour,\ncalled _liver of antimony_. If antimony be melted or boiled with a fixed\nalkali, a precipitate is made by cooling, called _kermes mineral_,\nformerly used in medicine. The antimonial preparations that are now most\nin use are _antimonial wine_ and _tartar emetic_. The wine is made by\ninfusing pulverized glass of antimony in Spanish wine some days, and\nfiltering the clear fluid through paper. The emetic tartar, or\nantimonial tartar, is a saline substance, composed of acid of tartar,\nvegetable alkali, and antimony partially calcined. The preparation may\nbe seen in the Dispensaries.\n\nThe regulus of antimony is used in the form of pills, which purge more\nor less in proportion to the acid they meet with; and as they undergo\nlittle or no change in passing through the body, they are called\n_perpetual pills_.\n\n\n_Of Manganese._\n\nManganese is a hard, black mineral, very ponderous, and the regulus of\nit is a semi-metal of a dull white colour when broken, but soon grows\ndark by exposure to the air. It is hard and brittle, though not\npulverizable, rough in its fracture, and of very difficult fusion. Its\ncalces are white when imperfect, but black, or dark green, when perfect.\nThe white calx is soluble in acids. When broken in pieces, it falls into\npowder by a spontaneous calcination, and this powder is magnetical,\nthough the mass was not possessed of that property. The black calx of\nmanganese is altogether insoluble in acids. It contains much\ndephlogisticated air.\n\nThe calx of manganese is used in making glass; the glass destroying the\ncolour of that of the other materials, and thereby making the whole mass\ntransparent.\n\nThis semi-metal mixes with most of the metals in fusion, but not with\nmercury.\n\nThere is another ore of manganese, called _black woad_, which inflames\nspontaneously when mixed with oil.\n\n\n_Of Wolfram._\n\nWolfram is a mineral of a brownish or black colour, found in the tin\nmines of Cornwall, of a radiated or foliated texture, shining almost\nlike a metal. It contains much of the calx of manganese, and iron; but\nwhen the substance is pulverized, these are easily dissolved, and the\ncalx of wolfram is found to be yellow.\n\nThis calx turns blue by exposure to light; and an hundred grains of it\nheated with charcoal will yield sixty grains of a peculiar metal, in\nsmall particles, which, when broken, look like steel. It is soluble in\nthe vitriolic or marine acids, and reduced to a yellow calx by nitrous\nacid or aqua regia.\n\n\n_Of Molybdena._\n\nMolybdena is a substance which much resembles plumbago; but its texture\nis scaly, and not easily pulverized, on account of a degree of\nflexibility which its laminae possess. With extreme heat, and mixed with\ncharcoal, it yields small particles of a metal that is grey, brittle,\nand extremely infusible; and uniting with several of the metals, it\nforms with them brittle or friable compounds. By heat it is converted\ninto a white calx.\n\n\n_Of Solid Combustible Substances._\n\nThere yet remains a class of solid substances, of the _combustible_\nkind, but most of them have been already considered under the form of\nthe fluids, from which they are originally formed, as _bitumen_,\n_pit-coal_, and _amber_; or under the principal ingredients of which\nthey are composed, as _sulphur_ and _plumbago_.\n\nThere only remains to be mentioned the _diamond_, which is of a nature\nquite different from that of the other precious stones, the principal\ningredient in which is siliceous earth, which renders them not liable to\nbe much affected by heat. On the contrary, the diamond is a combustible\nsubstance; for in a degree of heat somewhat greater than that which will\nmelt silver, it burns with a slight flame, diminishes common air, and\nleaves a soot behind. Also, if diamond powder be triturated with\nvitriolic acid, it turns it black, which is another proof of its\ncontaining phlogiston.\n\nThe diamond is valued on account of its extreme hardness, the exquisite\npolish it is capable of, and its extraordinary refractive power; for\nlight falling on its interior surface with an angle of incidence greater\nthan 24-1/2 will be wholly reflected, whereas in glass it requires an angle\nof 41 degrees.\n\n\n\n\nLECTURE XXIX.\n\n\n_Of the Doctrine of Phlogiston and the Composition of Water._\n\nIt was supposed to be a great discovery of Mr. Stahl, that all\ninflammable substances, as well as metals, contain a principle, or\nsubstance, to which he gave the name of phlogiston, and that the\naddition or deprivation of this substance makes some of the most\nremarkable changes in bodies, especially that the union of a metallic\ncalx and this substance makes a metal; and that combustion consists in\nthe separation of phlogiston from the substances that contain it. That\nit is the same principle, or substance, that enters into all inflammable\nsubstances, and metals, is evident, from its being disengaged from any\nof them, and entering into the composition of any of the others. Thus\nthe phlogiston of charcoal or inflammable air becomes the phlogiston of\nany of the metals, when the calx is heated in contact with either of\nthem.\n\nOn the contrary, Mr. Lavoisier and most of the French chemists, are of\nopinion, that there is no such principle, or substance, as phlogiston;\nthat metals and other inflammable bodies are simple substances, which\nhave an affinity to pure air; and that combustion consists not in the\nseparation of any thing from the inflammable substance, but in the union\nof pure air with it.\n\nThey moreover say, that water is not, as has been commonly supposed, a\nsimple substance, but that it consists of two elements, viz. pure air,\nor _oxygene_, and another, to which they give the name of _hydrogene_,\nwhich, with the principle of _heat_, called by them _calorique_, is\ninflammable air.\n\nThe principal fact adduced by them to prove that metals do not lose any\nthing when they become calces, but only gain something, is, that mercury\nbecomes a calx, called _precipitate per se_, by imbibing pure air, and\nthat it becomes running mercury again by parting with it.\n\nThis is acknowledged: but it is almost the only case of any calx being\nrevived without the help of some known phlogistic substance; and in this\nparticular case it is not absurd to suppose, that the mercury, in\nbecoming precipitate per se, may retain all its phlogiston, as well as\nimbibe pure air, and therefore be revived by simply parting with that\nair. In many other cases the same metal, in different states, contains\nmore or less phlogiston, as cast iron, malleable iron, and steel. Also\nthere is a calx of mercury made by the acid of vitriol, which cannot be\nrevived without the help of inflammable air, or some other substance\nsupposed to contain phlogiston: and that the inflammable air is really\nimbibed in these processes, is evident, from its wholly disappearing,\nand nothing being left in the vessel in which the process is made beside\nthe metal that is revived by it. If precipitate per se be revived in\ninflammable air, the air will be imbibed, so that running mercury may\ncontain more or less phlogiston.\n\nThe antiphlogistians also say, that the diminution of atmospherical air\nby the burning of phosphorus is a proof of their theory; the pure air\nbeing imbibed by that substance, and nothing emitted from it. But there\nis the same proof of phosphorus containing phlogiston, that there is of\ndry flesh containing it; since the produce of the solution of it in\nnitrous acid, and its effect upon the acid, are the same, viz. the\nproduction of phlogisticated air, and the phlogistication of the acid.\n\nTheir proof that water is decomposed, is, that in sending steam over hot\niron, inflammable air (which they suppose to be one constituent part of\nit) is procured; while the other part, viz. the oxygene, unites with the\niron, and adds to its weight. But it is replied, that the inflammable\nair may be well supposed to be the phlogiston of the iron, united to\npart of the water, as its base, while the remainder of the water is\nimbibed by the calx; and that it is mere water, and not pure air, or\noxygene, that is retained in the iron, is evident, from nothing but pure\nwater being recovered when this calx of iron is revived in inflammable\nair, in which case the inflammable air wholly disappears, taking the\nplace of the water, by which it had been expelled.\n\nIn answer to this it is said, that the pure air expelled from the calx\nuniting with the inflammable air in the vessel, recomposes the water\nfound after this process. But in every other case in which any substance\ncontaining pure air is heated in inflammable air, though the inflammable\nair be in part imbibed, some _fixed air_ is produced, and this fixed air\nis composed of the pure air in the substance and part of the inflammable\nair in the vessel. Thus, if _minium_, which contains pure air, and\n_massicot_, which contains none, be heated in inflammable air, in both\nthe cases lead will be revived by the absorption of inflammable air; but\nin the former case only, and not in the latter, will fixed air be\nproduced. The calx of iron, therefore, having the same effect with\nmassicot, when treated in the same manner, appears to contain no more\npure air than massicot does.\n\nBesides this explanation of the facts on which the new theory is\nfounded, which shews it to be unnecessary, the old hypothesis being\nsufficient for the purpose, some facts are alledged, as inconsistent\nwith the new doctrine.\n\nIf the calx of iron made by water, and charcoal made by the greatest\ndegree of heat, be mixed together, a great quantity of inflammable air\nwill be produced; though, according to the new theory, neither of these\nsubstances contained any water, which they maintain to be the only\norigin of it. But this fact is easily explained upon the doctrine of\nphlogiston; the water in this calx uniting with the phlogiston of the\ncharcoal, and then forming inflammable air; and it is the same kind of\ninflammable air that is made from charcoal and water.\n\nAlso the union of inflammable and pure air, when they are fired together\nby means of the electric spark, produces not pure water, as, according\nto the new theory, it ought to do, but _nitrous acid_.\n\nTo this it has been objected, that the acid thus produced came from the\ndecomposition of phlogisticated air, a small portion of which was at\nfirst contained in the mixture of the two kinds of air. But when every\nparticle of phlogisticated air is excluded, the strongest acid is\nprocured.\n\nThey find, indeed, that by the slow burning of inflammable air in pure\nair, they get pure water. But then it appears, that whenever this is the\ncase, there is a production of phlogisticated air, which contains the\nnecessary element of nitrous acid; and this is always the case when\nthere is a little surplus of the inflammable air that is fired along\nwith the pure air, as the acid is always procured when there is a\nredundancy of pure air.\n\nThat much water should be procured by the decomposition of these kinds\nof air, is easily accounted for, by supposing that water, or steam, is\nthe basis of these, as well as of all other kinds of air.\n\nSince air something better than that of the atmosphere is constantly\nproduced from water by converting it into vapour, and also by removing\nthe pressure of the atmosphere, and these processes do not appear to\nhave any limits; it seems probable, that _water_ united to the principle\nof _heat_; constitutes atmospherical air; and if so, it must consist of\nthe elements of both dephlogisticated and phlogisticated air; which is a\nsupposition very different from that of the French chemists.\n\n\n\n\nLECTURE XXX.\n\n\n_Of Heat._\n\nHeat is an affection of bodies well known by the sensation that it\nexcites. It is produced by friction or compression, as by the striking\nof flint against steel, and the hammering of iron, by the reflection or\nrefraction of light, and by the combustion of inflammable substances.\n\nIt has been long disputed, whether the cause of heat be properly a\n_substance_, or some particular affection of the particles that compose\nthe substance that is heated. But be it a substance, or a principle of\nany other kind, it is capable of being transferred from one body to\nanother, and the communication of it is attended with the following\ncircumstances. All substances are expanded by heat, but some in a\ngreater degree than others; as metals more than earthy substances, and\ncharcoal more than wood. Also some receive and transmit heat through\ntheir substance more readily than others; metals more so than earths,\nand of the metals, copper more readily than iron. Instruments contrived\nto ascertain the expansion of substances by heat, are called\n_pyrometers_, and are of various constructions.\n\nAs a standard to measure the degrees of heat, mercury is in general\npreferable to any other substance, on account of its readily receiving,\nand communicating, heat through its whole mass. _Thermometers_,\ntherefore, or instruments to measure the degrees of heat, are generally\nconstructed of it, though, as it is subject to become solid in a great\ndegree of cold, ardent spirit, which will not freeze at all, is more\nproper in that particular case.\n\nThe graduation of thermometers is arbitrary. In that of Fahrenheit,\nwhich is chiefly used in England, the freezing point of water is 32 deg.,\nand the boiling point 212 deg. In that of Reaumur, which is chiefly used\nabroad, the freezing point of water is 0, and the boiling point 80. To\nmeasure the degrees of heat above ignition, Mr. Wedgwood has happily\ncontrived to use pieces of clay, which contract in the fire; and he has\nalso been able to find the coincidence of the degrees in mercurial\nthermometers with those of his own.\n\nTo measure the degrees of heat and cold during a person's absence, Lord\nGeorge Cavendish contrived an instrument, in which a small bason\nreceived the mercury, that was raised higher than the place for which it\nwas regulated by heat or cold, without a power of returning. But Mr. Six\nhas lately hit upon a better method, viz. introducing into the tube of\nhis thermometer a small piece of iron, which is raised by the ascent of\nthe mercury, and prevented from descending by a small spring; but which\nmay be brought back to its former place by a magnet acting through the\nglass.\n\nHeat, like light, is propagated in right lines; and what is more\nremarkable, cold observes the same laws. For if the substance emitting\nheat without light, as iron below ignition, be placed in the focus of a\nburning mirror, a thermometer in the focus of a similar mirror, placed\nparallel to it, though at a considerable distance, will be heated by it,\nand if a piece of ice be placed there, the mercury will fall.\n\nHeat assists the solvent power of almost all menstrua; so that many\nsubstances will unite in a certain degree of heat, which will form no\nunion at all without it, as dephlogisticated and inflammable air.\n\nIf substances be of the same kind, they will receive heat from one\nanother, in proportion to their masses. Thus, if a quantity of water\nheated to 40 deg. be mixed with another equal quantity of water heated to\n20 deg., the whole mass will be heated to 30 deg. But if the substances be of\ndifferent kinds, they will receive heat from each other in different\nproportions, according to their _capacity_ (as it is called) of\nreceiving heat. Thus, if a pint of mercury of the temperature of 136 be\nmixed with a pint of water of the temperature of 50, the temperature of\nthe two after mixture will not be a medium between those two numbers,\nviz. 93, but 76; consequently the mercury was cooled 60 deg., while the\nwater was heated only 26; so that 26 degrees of heat in water correspond\nto 60 in mercury. But mercury is about 13 times specifically heavier\nthan water, so that an equal weight of mercury would contain only one\nthirtieth part of this heat; and dividing 26 by 13, the quotient is 2.\nIf _weight_, therefore, be considered, the heat discovered by water\nshould be reckoned as 2 instead of 60; and consequently when water\nreceives 2 degrees of heat, an equal weight of mercury will receive 60 deg.;\nand dividing both the numbers by 2, if the heat of water be 1, that of\nthe mercury will be 30. Or since they receive equal degrees of heat,\nwhether they discover it or not (and the less they discover, the more\nthey retain in a latent state) a pound of mercury contains no more than\none thirtieth part of the heat actually existing in a pound of water of\nthe same temperature. Water, therefore, is said to have a greater\ncapacity for receiving and retaining heat, without discovering it, than\nmercury, in the proportion of 30 to 1, if weight be considered, or of\n60 to 26, that is of 30 to 13; if _bulk_ be the standard, though,\naccording to some, it is as 3 to 2.\n\nThe capacity of receiving heat in the substance is greatest in a state\nof vapour, and least in that of a solid; so that when ice is converted\ninto water, heat is absorbed, and more still when it is converted into\nvapour; and on the contrary, when vapour is converted into water, it\ngives out the heat which it had imbibed, and when it becomes ice it\ngives out still more.\n\nIf equal quantities of ice and water be exposed to heat at the\ntemperature of 32 deg., the ice will only become water, without receiving\nany additional sensible heat; but an equal quantity of water in the same\nsituation would be raised to 178 deg., so that 146 degrees of heat will be\nimbibed, and remain in latent in the water, in consequence of its\npassing from a state of ice: and heat communicated by a given weight of\nvapour will raise an equal weight of a nonevaporable substance, of the\nsame capacity with water, 943 degrees; so that much more heat is latent\nin steam, than in the water from which it was formed.\n\nThis doctrine of latent heat explains a great variety of phaenomena in\nnature; as that of cooling bodies by evaporation, the vapour of water,\nor any other fluid substance, absorbing and carrying off the heat they\nhad before.\n\nWater, perfectly at rest, will fall considerably below the freezing\npoint, and yet continue fluid: but on the slightest agitation, the\ncongelation of the whole, or part of it, takes place instantly, and if\nthe whole be not solid, it will instantly rise to 32 deg., the freezing\npoint. From whatever cause, some motion seems necessary to the\ncommencement of congelation, at least in a moderate temperature; but\nwhenever any part of the water becomes solid, it gives out some of the\nheat it had before, and that heat which was before latent becoming\nsensible, and being diffused through the whole mass, raises its\ntemperature.\n\nOn the same principle, when water heated higher than the boiling point\nin a digester is suddenly permitted to escape in the form of steam, the\nremainder is instantly reduced to the common boiling point, the heat\nabove that point being carried off in a latent state by the steam.\n\nHad it not been for this wise provision in nature, the whole of any\nquantity of water would, in all cases of freezing, have become solid at\nonce; and also the whole of any quantity that was heated to the point of\nboiling, would have been converted into steam at once; circumstances\nwhich would have been extremely inconvenient, and often fatal.\n\nThis doctrine also explains the effect of freezing mixtures, as that of\nsalt and snow. These solid substances, on being mixed, become fluid, and\nthat fluid absorbing much heat, deprives all the neighbouring bodies of\npart of what they had. But if the temperature at which the mixture is\nmade be as low as that to which this mixture would have brought it, it\nhas no effect, and in a lower temperature this new fluid would become\nsolid; for that mixture has only a certain determinate capacity for\nheat, and if the neighbouring bodies have less heat, they will take\nfrom it.\n\nIt has been observed, that the comparative heat of bodies containing\nphlogiston is increased by calcination or combustion; so that the calx\nof iron has a greater capacity for heat, and therefore contains more\nlatent heat, than the metal.\n\nIn general it is not found, that the same substances have their capacity\nfor receiving heat increased by an increase of temperature; but this is\nsaid to be the case with a mixture of ardent spirit and water, and also\nthat of spirit of vitriol and water.\n\nSince all substances contain a greater or less quantity of heat, and in\nconsequence of being deprived of it become colder and colder, it is a\nquestion of some curiosity to determine the extent to which this can go,\nor at what degree in the scale of a thermometer any substance would be\nabsolutely cold, or deprived of all heat; and an attempt has been made\nto solve this problem in the following manner. Comparing the capacity of\nwater with that of ice, by means of a third substance, viz. mercury, it\nhas been found, that if that of ice be 9 deg., that of water is 10 deg.; so that\nwater in becoming ice gives out one tenth part of its whole quantity of\nheat. But it has been shown, that ice in becoming water absorbs 146\ndegrees of heat. This, therefore, being one tenth part of the whole heat\nof water, it must have contained 1460 degrees; so that taking 32\ndegrees, which is the freezing point, from that number, the point of\nabsolute cold will be 1426 below 0 of Fahrenheit's scale.\n\nBy a computation, made by means of the heat of inflammable and\ndephlogisticated air, at the temperature of 50, Dr. Crawford finds, that\nit contains nearly 1550 degrees of heat; so that the point of absolute\ncold will be 1500 below 0. But more experiments are wanted to solve this\ncurious problem to entire satisfaction.\n\n\n\n\nLECTURE XXXI.\n\n\n_Of Animal Heat._\n\nSince all animals, and especially those that have red blood, are much\nhotter than the medium in which they live, the source of this heat has\nbecome the subject of much investigation; and as the most probable\ntheory is that of Dr. Crawford, I shall give a short detail of the\nreasons on which it is founded.\n\nHaving, with the most scrupulous attention, ascertained the _latent_,\nor, as he calls it, the _absolute_ heat of blood, and also that of the\naliments of which it is composed, he finds that it contains more than\ncould have been derived from _them_. Also finding that the absolute heat\nof arterial blood exceeds that of venous blood, in the proportion of 11-1/2\nto 10, he concludes that it derives its heat from the air respired in\nthe lungs, and that it parts with this _latent_ heat, so that it becomes\nsensible, in the course of its circulation, in which it becomes loaded\nwith phlogiston, which it communicates to the air in the lungs.\n\nThat this heat is furnished by the _air_, he proves, by finding, that\nthat which we inspire contains more heat than that which we expire, or\nthan the aqueous humor which we expire along with it, in a very\nconsiderable proportion; so that if the heat contained in the pure air\ndid not become latent in the blood, it would raise its temperature\nhigher than that of red-hot iron. And again, if the venous blood, in\nbeing converted into arterial blood, did not receive a supply of latent\nheat from the air, its temperature would fall from 96 to 104 below 0 in\nFahrenheit's thermometer.\n\nThat the heat procured by combustion has the same source, viz. the\ndephlogisticated air that is decomposed in the process, is generally\nallowed; and Dr. Crawford finds, that when equal portions of air are\naltered by the respiration of a Guinea pig, or by the burning of\ncharcoal, the quantity of heat communicated by the two processes is\nnearly equal.\n\nThe following facts are also alleged in favour of his theory. Whereas\nanimals which have much red blood, and respire much, have the power of\nkeeping themselves in a temperature considerably higher than that of the\nsurrounding atmosphere, other animals, as _frogs_ and _serpents_, are\nnearly of the same temperature with it; and those animals which have the\nlargest respiratory organs, as birds, are the warmest; also the degree\nof heat is in some measure proportionable to the quantity of air that is\nrespired in a given time, as in violent exercise.\n\nIt has been observed, that animals in a medium hotter than the blood\nhave a power of preserving themselves in the same temperature. In this\ncase the heat is probably carried off by perspiration, while the blood\nceases to receive, or give out, any heat; and Dr. Crawford finds, that\nwhen an animal is placed in a warm medium the colour of the venous blood\napproaches nearer to that of the arterial than when it is placed in a\ncolder medium; and also, that it phlogisticates the air less than in the\nformer case; so that in these circumstances respiration has not the same\neffect that it has in a colder temperature, in giving the body an\nadditional quantity of heat; which is an excellent provision in nature,\nas the heat is not wanted, but, on the contrary, would prove\ninconvenient.\n\n\n\n\nLECTURE XXXII.\n\n\n_Of Light._\n\nAnother most important agent in nature, and one that has a near\nconnexion with heat, is _light_, being emitted by all bodies in a state\nof ignition, and especially by the sun, the great source of light and of\nheat to this habitable world.\n\nWhether light consists of particles of matter (which is most probable)\nor be the undulation of a peculiar fluid, filling all space, it is\nemitted from all luminous bodies in right lines.\n\nFalling upon other bodies, part of the light is _reflected_ at an angle\nequal to that of its incidence, though not by impinging on the\nreflecting surface, but by a power acting at a small distance from it.\nBut another part of the light enters the body, and is _refracted_ or\nbent _towards_, or _from_, the perpendicular to the surface of the new\nmedium, if the incidence be oblique to it. In general, rays of light\nfalling obliquely on any medium are bent as if they were attracted by\nit, when it has a greater density, or contains more of the inflammable\nprinciple, than the medium through which it was transmitted to it. More\nof the rays are reflected when they fall upon a body with a small degree\nof obliquity to its surface, and more of them are transmitted, or enter\nthe body, when their incidence is nearer to a perpendicular.\n\nThe velocity with which light is emitted or reflected is the same, and\nso great that it passes from the sun to the earth in about eight\nminutes and twelve seconds.\n\nRays of light emitted or reflected from a body entering the pupil of the\neye, are so refracted by the humours of it, as to be united at the\nsurface of the retina, and so make images of the objects, by means of\nwhich they are visible to us; and the magnifying power of telescopes or\nmicroscopes depends upon contriving, by means of reflections or\nrefractions, that pencils of rays issuing from every point of any object\nshall first diverge, and then converge, as they would have done from a\nmuch larger object, or from one placed much nearer to the eye.\n\nWhen a beam of light is bent out of its course by refraction, all the\nrays of which it consists are not equally refracted, but some of them\nmore and others less; and the colour which they are disposed to exhibit\nis connected invariably with the degree of their refrangibility; the\nred-coloured rays being the least, and the violet the most refrangible,\nand the rest being more or less so in proportion to their nearness to\nthese, which are the extremes, in the following order, violet, indigo,\nblue, green, yellow, orange, red.\n\nThese colours, when separated as much possible, are still contiguous;\nand all the shades of each colour have likewise their separate and\ninvariable degrees of refrangibility. When separated as distinctly as\npossible, they divide the whole space between them exactly as a musical\nchord is divided in order to found the several notes and half notes of\nan octave.\n\nThese differently-coloured rays of light are also separated in passing\nthrough the transparent medium of air and water, in consequence of which\nthe sky appears blue and the sea green, these rays being returned, while\nthe red ones proceed to a greater distance. By this means also objects\nat the bottom of the sea appear to divers red, and so do all objects\nenlightened by an evening sun.\n\nThe mixture of all the differently-coloured rays, in the proportions in\nwhich they cover the coloured image above mentioned, makes a _white_,\nand the absence of all light is _blackness_.\n\nBy means of the different refrangibility of light, the colours of the\nrainbow may be explained.\n\nThe distance to which the differently-coloured rays are separated from\neach other is not in proportion to the mean refractive power of the\nmedium, but depends upon the peculiar constitution of the substance by\nwhich they are refracted. The _dispersing power_ of glass, into the\ncomposition of which _lead_ enters, is great in proportion to the mean\nrefraction; and it is proportionally little in that glass in which there\nis much alkaline salt. The construction of _achromatic telescopes_\ndepends upon this principle.\n\nNot only have different rays of light these different properties with\nrespect to bodies, so as to be more or less refracted, or dispersed, by\nthem, but different sides of the same rays seem to have different\nproperties, for they are differently affected on entering a piece of\n_island crystal_. With the same degree of incidence; part of the pencil\nof rays, consisting of all the colours, proceeds in one direction, and\nthe rest in a different one; so that objects seen through a piece of\nthis substance appear double.\n\nAt the surface of all bodies rays of light are promiscuously reflected,\nor transmitted.\n\nBut if the next surface be very near to it, the rays of one colour\nchiefly are reflected, and the rest transmitted, and these places occur\nalternately for rays of each of the colours in passing from the thinnest\nto the thickest parts of the medium; so that several series, or orders,\nof colours will be visible on the surface of the same thin transparent\nbody. On this principle coloured rings appear between a plane and a\nconvex lens, in a little oil on the surface of water, and in bubbles\nmade with soap and water.\n\nWhen rays of light pass near to any body, so as to come within the\nsphere of its attraction and repulsion, an _inflection_ takes place; all\nthe kinds of rays being bent _towards_, or _from_, the body, and these\npowers affecting some rays more than others, they are by this means also\nseparated from each other, so that coloured streaks appear both within\nthe shadow, and the outside of it, the red rays being inflected at the\ngreatest distance from the body.\n\nPart of the light which enters bodies is retained within them, and\nproceeds no farther; but so loosely in some kinds of bodies, that a\nsmall degree of heat is sufficient to expel it again, so as to make the\nbody visible in the dark: but the more heat is applied, the sooner is\nall the light expelled. This is a strong argument for the materiality of\nlight. _Bolognian phosphorus_ is a substance which has this property;\nbut a composition made by Mr. Canton, of calcined oyster-shells and\nsulphur, in a much greater degree. However, white paper, and most\nsubstances, except the metals, are possessed of this property in a small\ndegree.\n\nSome bodies, especially phosphorus, and animal substances tending to\nputrefaction, emit light without being sensibly hot.\n\nThe _colours_ of vegetables, and likewise their _taste_ and _smell_,\ndepend upon light. It is also by means of light falling on the leaves\nand other green parts of plants, that they emit dephlogisticated air,\nwhich preserves the atmosphere fit for respiration.\n\nIt is light that imparts colour to the skins of men, by means of the\nfluid immediately under them. This is the cause of _tanning_, of the\n_copper colour_ of the North Americans, and the _black_ of the Negroes.\nLight also gives colour to several other substances, especially the\nsolutions of mercury in acids.\n\n\n\n\nLECTURE XXXIII.\n\n\n_Of Magnetism._\n\nMagnetism is a property peculiar to iron, or some ores of it. The earth\nitself, owing probably to the iron ores contained in it, has the same\nproperty. But though all iron is acted upon by magnetism, _steel_ only\nis capable of having the power communicated to it.\n\nEvery magnet has two poles, denominated _north_ and _south_, each of\nwhich attracts the other, and repels that of the same kind with itself.\nIf a magnet be cut into two parts, between the two poles, it will make\ntwo magnets, the parts that were contiguous becoming opposite poles.\n\nThough the poles of a magnet are denominated _north_ and _south_, they\ndo not constantly, and in all parts of the earth, point due north or\nsouth, but in most places to the east or west of them, and with a\nconsiderable variation in a course of time. Also a magnet exactly\nbalanced at its center will have a declination from an horizontal\nposition of about 70 degrees. The former is called the _variation_, and\nthe latter the _dipping_ of the magnetic needle.\n\nA straight bar of iron which has been long fixed in a vertical position,\nwill become a magnet, the lower end becoming a north pole, and the upper\nend a south one; for if it be suspended horizontally, the lower end will\npoint towards the north, and the upper end towards the south. Also any\nbar of iron, not magnetical, held in a vertical position, will become a\ntemporary magnet, the lower end becoming a north pole, and the upper end\na south one; and a few strokes of a hammer will fix the poles for a\nshort time, though the position of the ends be changed. Magnetism may\nlikewise be given to a bar of iron by placing it firmly in the position\nof the dipping-needle, and rubbing it hard one way with a polished steel\ninstrument. Iron will also become magnetical by ignition and quenching\nit in water in the position of the dipping-needle.\n\nMagnetism acts, without any diminution of its force, through any medium;\nand iron not magnetical will have that power while it is in connexion\nwith a magnet, or rather the power of the magnet is extended through the\niron.\n\nSteel filings gently thrown upon a magnet, adhere to it in a curious\nmanner; and the filings, acquiring magnetism by the contact, adhere\ntogether, and form a number of small magnets, which arrange themselves\naccording to the attraction of the poles of the original magnet. This\nexperiment is made to the most advantage upon a piece of pasteboard, or\npaper, placed over the magnet.\n\nMagnetism is communicated by the friction, or the near position, of a\nmagnet to a piece of steel of a size less than it. For this reason a\ncombination of magnetical bars will have a greater effect than a single\none; and in the following manner, beginning without any magnetism at\nall, the greatest quantity may be procured. Six bars of steel may be\nrendered slightly magnetical by fixing each of them successively to an\nupright poker, and stroking it several times from the bottom to the top\nwith the lower end of an old pair of tongs. If then four of these bars\nbe joined, the magnetism of the remaining two will be much increased by\na proper method of rubbing with them; and by changing their places,\njoining the strongest, and acting upon the weakest, they may all be made\nas magnetical as they are capable of being.\n\nThe strength of a natural magnet may be increased by covering its polar\nextremities with steel. This is called the _arming_ of the loadstone.\n\nTo account for the variation of the needle, Dr. Halley supposed the\nearth to consist of two parts, an external _shell_ and an internal\n_nucleus_, detached, and having a revolution distinct from it; and that\nthe action of the poles of the shell and of the nucleus would explain\nall the varieties in the position of the needle. But others think that\nthe cause of the magnetism of the earth is not _within_, but _without_\nitself. One reason for this opinion is, that a magnet is liable to be\naffected by a strong aurora borealis; and another is, that the variation\nof the needle proceeds in such manner as supposes that the motion of the\nnucleus must be quicker than that of the shell of the earth; whereas,\nsince it is most natural to suppose that motion was communicated to the\nnucleus by the shell, it would be slower.\n\nSome idea of the quantity and the progress of the variation of the\nneedle may be formed from the following facts.--At the Cape of Good\nHope, when it was discovered by the Portuguese, in 1486, there was no\nvariation, the needle there pointing due north; in 1622 it was about 2\ndegrees westward, in 1675 it was 8 deg. W. in 1700 about 11 deg. W. in 1756\nabout 18 deg. W. and in 1774 about 21-1/2 deg. W. In London, in 1580, the variation\nwas 11 degrees 15 seconds E.; in 1622 it was 6 deg. E. in 1634 it was 4 deg.\n5 min. E. in 1657 it was nothing at all; in 1672 it was 2 deg. 30 min.\nW. in 1692 it was 6 deg. W. in 1753 it was about 16 W. and at present it\nis about 21 W.\n\nThe longitude may in some places be found by the variation of the\nneedle; and Mr. Churchman, of America, having given much attention to\nthe subject, comparing the observations of others, and many of his own,\nthinks that he has found a method of determining the longitude to a\ngreat degree of certainty, in most cases, by this means.\n\nHe says there are two magnetic poles of the earth, one to the north and\nthe other to the south, at different distances from the poles of the\nearth, and revolving in different times; and from the combined influence\nof these two poles he deduces rules for the position of the needle in\nall places of the earth, and at all times, past, present, or to come.\n\nThe north magnetic pole, he says, makes a complete revolution in 426\nyears, 77 days, 9 hours, and the south pole in about 5459 years. In the\nbeginning of the year 1777 the north magnetic pole was in 76 deg. 4 min.\nnorth latitude; and in longitude from Greenwich 140 deg. east; and the\nsouth was in 72 deg. south latitude, and 140 deg. east from Greenwich.\n\n\n\n\nLECTURE XXXIV.\n\n\n_Of Electricity._\n\nElectricity is a property belonging to, or capable of being communicated\nto, all substances whatever; and whereas by some of them it is\ntransmitted with great ease, and by others with much difficulty, they\nhave been divided into two classes, and denominated _conductors_ or\n_non-conductors_ of electricity. Also the latter receiving this power by\nfriction, and other means, are termed _electrics_, and the former\n_non-electrics_.\n\nMetals of all kinds, and water, are conductors, though in very different\ndegrees; so also is charcoal. All other substances, and also a perfect\nvacuum, are non-conductors of electricity. But many of these substances,\nwhen they are made very hot, as glass, resin, baked wood, and perhaps\nall the rest on which the experiment can be made in this state, are\nconductors.\n\nIt is the property of all kinds of electrics, when they are rubbed by\nbodies different from themselves, to attract light substances of all\nkinds, to exhibit an appearance of _light_, attended with a particular\n_sound_, on the approach of any conductor; and if the nostrils are\npresented, they are affected with a _smell_ like that of phosphorus.\nThis attraction is most easily explained by supposing that electricity\nis produced by a fluid exceedingly elastic, or repulsive of itself, and\nattracted by all other substances.\n\nAn electric exhibiting the appearances above mentioned, is said to be\n_excited_, and some of them, particularly the _tourmaline_, are excited\nby heating and cooling, as well as by friction. It appears, however,\nthat excitation consists in the mere transferring of electricity from\none substance to another, and that the great source of electricity is in\nthe earth. On this account it is necessary to the considerable\nexcitation of any electric, that the substance against which it is\nrubbed (hence termed _the rubber_) have a communication with the earth,\nby means of conductors; for if the rubber be _insulated_, that is cut\noff from all communication with the earth by means of electrics, the\nfriction has but little effect.\n\nWhen insulated bodies have been attracted by, and brought into contact\nwith, an excited electric, they begin to be repelled by it, and also to\nrepel one another; nor will they be attracted again till they have been\nbrought into contact with some conductor communicating with the earth;\nbut after this they will be attracted as at first.\n\nIf conductors be _insulated_, electric powers may be communicated to\nthem by the approach of excited electrics, or the contact of other\nelectrified bodies. They will then attract light bodies, and give\nsparks, &c. like the excited electrics themselves.\n\nWhen electricity is strongly communicated to insulated animal bodies,\nthe pulse is quickened, and perspiration increased; and if they receive,\nor part with, their electricity on a sudden, a painful sensation is felt\nat the place of communication. But what is more extraordinary, is, that\nthe influence of the brain and nerves upon the muscles seems to be of an\nelectric nature.\n\nThis is one of the last and most important of all philosophical\ndiscoveries. I shall, therefore, give the result of all the observations\nthat have hitherto been made on the subject, in a _series of\npropositions_, drawn up by an intelligent friend, who has given much\nmore attention to it than I have done.\n\n1. The nerve of the limb of an animal being laid bare, and surrounded\nwith a piece of sheet lead, or of tinfoil, if a communication be formed\nbetween the nerve thus armed and any of the neighbouring muscles, by\nmeans of a piece of zinc, strong contractions will be produced in the\nlimb.\n\n2. If a portion of the nerve which has been laid bare be armed as above,\ncontractions will be produced as powerfully, by forming the\ncommunication between the armed and bare part of the nerve, as between\nthe armed part and muscle.\n\n3. A similar effect is produced by arming a nerve and simply touching\nthe armed part of the nerve with the metallic conductor.\n\n4. Contractions will take place if a muscle be armed, and a\ncommunication be formed by means of the conductor between it and a\nneighbouring nerve. The same effect will be produced if the\ncommunication be formed between the armed muscle and another muscle,\nwhich is contiguous to it.\n\n5. Contractions may be produced in the limb of an animal by bringing the\npieces of metal into contact with each other at some distance from the\nlimb, provided the latter make part of a line of communication between\nthe two metallic conductors.\n\nThe experiment which proves this is made in the following manner. The\namputated limb of an animal being placed upon a table, let the operator\nhold with one hand the principal nerve, previously laid bare, and in the\nother let him hold a piece of zinc; let a small plate of lead or silver\nbe then laid upon the table, at some distance from the limb, and a\ncommunication be formed, by means of water, between the limb and the\npart of the table where the metal is lying. If the operator touch the\npiece of silver with the zinc, contractions will be produced in the limb\nthe moment that the metals come into contact with each other. The same\neffect will be produced if the two pieces of metal be previously placed\nin contact, and the operator touch one of them with his finger. This\nfact was discovered by Mr. William Cruikshank.\n\n6. Contractions can be produced in the amputated leg of a frog, by\nputting it into water, and bringing the two metals into contact with\neach other at a small distance from the limb.\n\n7. The influence which has passed through, and excited contractions in,\none limb, may be made to pass through, and excite contractions in,\nanother limb. In performing this experiment it is necessary to attend to\nthe following circumstances: let two amputated limbs of a frog be taken;\nlet one of them be laid upon a table, and its foot be folded in a piece\nof silver; let a person lift up the nerve of this limb with a silver\nprobe, and another person hold in his hand a piece of zinc, with which\nhe is to touch the silver including the foot; let the person holding the\nzinc in one hand catch with the other the nerve of the second limb, and\nhe who touches the nerve of the first limb is to hold in his other hand\nthe foot of the second; let the zinc now be applied to the silver\nincluding the foot of the first limb, and contractions will immediately\nbe excited in both limbs.\n\n8. The heart is the only involuntary muscle in which contractions can be\nexcited by these experiments.\n\n9. Contractions are produced more strongly, the farther the coating is\nplaced from the origin of the nerve.\n\n10. Animals which were almost dead have been found to be considerably\nrevived by exciting this influence.\n\n11. When these experiments are repeated upon an animal that has been\nkilled by opium, or by the electric shock, very slight contractions are\nproduced; and no contractions whatever will take place in an animal that\nhas been killed by corrosive sublimate, or that has been starved to\ndeath.\n\n12. Zinc appears to be the best exciter when applied to gold, silver,\nmolybdena, steel, or copper. The latter metals, however, excite but\nfeeble contractions when applied to each other. Next to zinc, in contact\nwith these metals, tin and lead, and silver and lead, appear to be the\nmost powerful exciters.\n\nAt least two kinds of fishes, the _torpedo_ and the _electrical eel_,\nhave a voluntary power of giving so strong a shock to the water in which\nthey swim, as to affect fishes and other animals which come near them;\nand by a conducing communication between different parts of these\nfishes, an electric shock may be given exactly like that of the Leyden\nphial, which will be described hereafter; and if the communication be\ninterrupted, a flash of electric light will be perceived.\n\nThe growth of vegetables is also quickened by electricity.\n\n\n\n\nLECTURE XXXV.\n\n\n_The same Subject continued._\n\nNo electric can be excited without producing electric appearances in the\nbody with which it is excited, provided that body be insulated; for this\ninsulated rubber will attract light bodies, give sparks, and make a\nsnapping noise, upon the approach of a conductor, as well as the excited\nelectric.\n\nIf an insulated conductor be pointed, or if a pointed conductor,\ncommunicating with the earth, be held pretty near it, little or no\nelectric appearance will be exhibited, only a light will appear at each\nof the points during the act of excitation, and a current of air will be\nsensible from off them both.\n\nThe effect of pointed bodies is best explained on the supposition of the\nelectric matter in one body repelling that in another; and consequently\nthe electricity belonging to a body with a large surface making a\ngreater resistance to the entrance of foreign electricity than that\nbelonging to a smaller.\n\nThese two electricities, viz. that of the excited electric, and that of\nthe rubber, though similar to, are the reverse of, one another. A body\nattracted by the one will be repelled by the other, and they will\nattract, and in all respects act upon, one another more sensibly than\nupon other bodies; so that two pieces of glass or silk possessed of\ncontrary electricities will cohere firmly together, and require a\nconsiderable force to separate them.\n\nThese two electricities having been first discovered by producing one of\nthem from glass, and the other from amber, sealing-wax, sulphur, rosin,\n&c. first obtained the names of _vitreous_ and _resinous_ electricity;\nand it being afterwards imagined that one of them was a redundancy, and\nthe other a deficiency, of a supposed electric fluid, the former has\nobtained the name of _positive_, and the latter that of _negative_,\nelectricity; and these terms are now principally in use.\n\nPositive and negative electricity may be distinguished from each other\nby the manner in which they appear at the points of bodies. From a\npointed body electrified positively, there issues a stream of light,\ndivided into denser streams, at the extremities; whereas, when the point\nis electrified negatively, the light is more minutely divided, and\ndiffused equally. The former of these is called a _brush_, and the\nlatter a _star_.\n\nIf a conductor not insulated be brought within the atmosphere (that is\nthe sphere of action) of any electrified body, it acquires the\nelectricity opposite to that of the electrified body, and the nearer it\nis brought, the stronger opposite electricity does it acquire, till the\none receive a spark from the other, and then the electricity of both\nwill be discharged.\n\nThe electric substance which separates the two conductors possessing\nthese two opposite kinds of electricity, is said to be _charged_.\nPlates of glass are the most convenient for this purpose, and the\nthinner the plate the greater is the charge it is capable of holding.\nThe conductors contiguous to each side of the glass are called their\n_coating_.\n\nAgreeably to the above-mentioned general principle, it is necessary that\none side of the charged glass have a communication with the rubber,\nwhile the other receives the electricity from the conductor, or with the\nconductor, while the other receives from the rubber.\n\nIt follows also, that the two sides of the plate thus charged are always\npossessed of the two opposite electricities; that side which\ncommunicates with the excited electric having the electricity of the\nelectric, and that which communicates with the rubber, that of the\nrubber.\n\nThere is, consequently, a very eager attraction between these two\nelectricities with which the different sides of the plate are charged,\nand when a proper communication is made by means of conductors, a flash\nof electric light, attended with a report (which is greater or less in\nproportion to the quantity of electricity communicated to them, and the\ngoodness of the conductors) is perceived between them, and the\nelectricity of both sides is thereby discharged.\n\nThe substance of the glass itself in, or upon, which these electricities\nexist, is impervious to electricity, and does not permit them to unite;\nbut if they be very strong, and the plate of glass very thin, they will\nforce a passage through the glass. This, however, always breaks the\nglass, and renders it incapable of another charge.\n\nThe flash of light, together with the explosion between the two opposite\nsides of a charged electric, is generally called the _electric shock_,\non account of the disagreeable sensation it gives any animal whose body\nis made use of to form the communication been them.\n\nThe electric shock is always found to perform the circuit from one side\nof the charged glass to the other by the shortest passage through the\nbest conductors. Common communicated electricity also observes the same\nrule in its transmission from one body to another.\n\nIt has not been found, that the electric shock takes up any sensible\nspace of time in being transmitted to the greatest distances.\n\nThe electric shock, as also the common electric spark, displaces the air\nthrough which it passes; and if its passage from conductor to conductor\nbe interrupted by non-conductors of a moderate thickness, it will rend\nand tear them in its passage, in such a manner as to exhibit the\nappearance of a sudden expansion of the air about the center of the\nshock.\n\nIf the electric circuit be interrupted, the electric matter, during the\ndischarge, will pass to any other body that lies near its path, and\ninstantly return. This may be called the _lateral explosion_. The effect\nof this lateral explosion through a brass chain, when the quantity of\nelectricity is very great, will be the discolouring and partial burning\nof the paper on which it lies.\n\nIf a great quantity of electricity be accumulated, as in a _battery_,\nthe explosion will pass over the surfaces of imperfect conductors\nwithout entering them, and the effect will be a strong _concussion_ of\nthe substance. Also the electric matter thus accumulated and condensed\nwill, by its repulsion, form _concentric circles_, which will appear by\nmelting the surface of a flat piece of metal on which the explosion is\nreceived.\n\nIf an electric shock, or strong spark, be made to pass through, or over,\nthe belly of a muscle, it forces it to contract, as in a convulsion.\n\nIf a strong shock be sent through a small animal body, it will often\ndeprive it instantly of life.\n\nWhen the electric shock is very strong, it will give polarity to\nmagnetic needles, and sometimes it reverses their poles.\n\nGreat shocks, by which animals are killed, are said to hasten\nputrefaction.\n\nElectricity and lightning are in all respects the same thing; since\nevery effect of lightning may be imitated by electricity, and every\nexperiment in electricity may be made with lightning, brought down from\nthe clouds by means of insulated pointed rods of metal.\n\n\n\n\nLECTURE XXXVI.\n\n\n_The same Subject continued._\n\nThree curious and important instruments, which are among the latest\nimprovements in electricity, deserve a particular explanation, and in\nall of them the effect depends upon the general principles mentioned\nabove, viz. that bodies placed within the influence, or, as it is\nusually termed, within the atmosphere, of an electrified body, are\naffected by a contrary electricity, and that these two electricities\nmutually attract each other. These instruments are the _electrophorus_,\nthe _condenser_ of electricity, and the _doubler_ of it.\n\nThe electrophorus consists of an insulated conducting plate applied to\nan insulated electric. If the latter have any electricity communicated\nto it, for example the negative, the positive electricity of the former\nwill be attracted by it, and consequently the plate will be capable of\nreceiving electricity from any body communicating with the earth; being,\nin this situation, capable of containing more electricity than its\nnatural quantity. Consequently, when it is removed from the lower plate,\nand the whole of its electricity equally diffused through it, it will\nappear to have a redundance, and therefore will give a spark to any body\ncommunicating with the earth. Being then replaced upon the electric, and\ntouched by any body communicating with the earth, it will be again\naffected as before, and give a spark on being raised; and this process\nmay be continued at pleasure, the electrophorus supplying the place of\nany other electrical machine.\n\nIf the conducting plate of the electrophorus be applied to a piece of\ndry wood, marble, or any other substance through which electricity can\npass but very slowly, or if the insulated conducting plate be covered\nwith a piece of thin silk, which will make some resistance to the\npassage of electricity, and it be then applied to another plate\ncommunicating with the earth; and if, in either of these cases, a body\nwith a large surface possessed of a weak electricity be applied to the\nconducting plate, the weak electricity not being able to overcome the\nobstruction presented to it, so as to be communicated to the other\nplate, will affect it with the contrary electricity, and this reacting\non the first plate, will condense its electricity on that part of the\nplate to which it is contiguous; in consequence of which its capacity of\nreceiving electricity will be increased; so that on the separation of\nthe two plates, that electricity which was before condensed, being\nequally diffused through the whole plate, will have a greater intensity\nthan it had before, attracting light bodies, or even giving a spark,\nwhen the body from which it received its electricity was incapable of\nit. For though it contained a great quantity of electricity, it was\ndiffused through so large a space that its intensity was very small.\nThis instrument is therefore called a _condenser of electricity_.\n\nIf an insulated plate of metal possessing the smallest degree of\nelectricity be presented very near to another plate communicating with\nthe earth, it will affect this plate with the opposite electricity; and\nthis being, in the same manner, applied to a third plate, will put it\ninto the same state with the first. If then these two plates be joined,\nand the first plate be presented to either of them, its own electricity\nbeing attracted by that of the plate presented, that of the other will\nbe drawn into it, so that its quantity will be doubled. The same process\nbeing repeated, will again double the electricity of this plate, till,\nfrom being quite insensible to the most exquisite electrometer, it will\nbecome very conspicuous, or even give sparks. This instrument is\ntherefore called a _doubler of electricity_, of excellent use in\nascertaining the quality of atmospherical electricity when ever so\nsmall. If this instrument be so constructed that these three plates can\nbe successively presented to one another by the revolution of one of\nthem on an axis, it is called the _revolving doubler_; and in this form\nit is most convenient for use.\n\n\nTHE END.\n\n\n    Transcriber's Note: Details of corrections\n\n    |Position                            |Original     |Correction    |\n    |                                    |             |              |\n    |Lecture I, first paragraph          |limestone    |lime-stone    |\n    |Lecture I, last paragraph           |_attraction_ |_attraction_, |\n    |Lecture III, first paragraph        |viz          |viz.          |\n    |Lecture III, last paragraph         |1.           |1             |\n    |Lecture XVII, penultimate paragraph |dissoved     |dissolved     |\n    |Lecture XIX, \"Of Calcareous Earth\"  |hundreth     |hundredth     |\n    |Lecture XXVI, \"Of Semi-metals\"      |ignates      |ignites       |\n    |Lecture XXVIII, first paragraph     |animony      |antimony      |","title":"Heads of Lectures on a Course of Experimental Philosophy: Particularly Including Chemistry","tradition":"philosophy-ethics","translated_text":null,"word_count":32308}