""■•5.B m m m as* m EXPERIMENTS AND OBSERVATIONS O N A N I M A L HEAT, AND T H I INFLAMATION O F COMBUSTIBLEBODIES. BEING AN ATTEMPT TO RESOLVE THESE PHENOMENA INTO A GENERAL LAW OF NATURE. BY ADAIR CRAWFORD, A. M. PHILADELPHIA: HUNTED FOR. THOMAS DOBSON, IN SECOND-STREET, BETWKBN MARKET AND CHESNUT-STREET. M,DCC,LXXXVII. T O JOHN W ATKINS ON, M. D. DISTINGUISHED BV HIS SKILL IN THE ART OF MEDICINE, BY HIS KNOWLEBGE IN PHILOSOPHY and POLITE LITERATURE; AND BY THOSE PRINCIPLES OF PROBITY AND HONOUR, WHICH SECURE THE ATTACHMENTS OF FRIENDSHIP, AND THE CONFIDENCE OF SOCIETY, THESE EXPERIMENTS AND OBSERVATIONS ARE INSCRIBED, BY HIS MOST SINCERE FRIEND, AND OBLIGED HUMBLE SERVANT, THE AUTHOR. A 2 ADVERTISEMENT. JLT is proper to apprize the reader who would wifh to repeat the experiments recited in the following pages, that fuch experi- ments are liable to be affected by a variety of adventitious circum- ftances, fo minute as to require the mod attentive obfervation. A change in the temperature of the air in the room, a variation in the time that is employed in mixing together the fubltances which are to have their comparative heats determined, a difference in the fhape of the veffcl, or in the degree of agitation that is given to the mixture, will often produce a confiderable diverfity jn the refult of the fame experiment. It is poffible however, by a feries of repeated trials, with well conftrudled thermometers, in the fame circumftances, to make a very near approximation to the truth, and, from a coincidence of facts, to obtain a degree of evi- dence, on which the mind may reft with entire confidence. Much time and labour have been employed in endeavouring to render the following experiments accurate: But if, after all, feme miftakes of lefs moment fhould be difcovered, it is hoped that the candour of the public will excufe them, as the author is perfuaded, that the facts from which the general conclufions have been drawn, are well founded. EXPERIMENTS AND OBSERVATIONS UPON ANIMAL HEAT, &c. .<..<..<..«..<..<^^<^»..>..>..,,.,..»« I HE words heat and fire are ambiguous. Heat in common language, has a double fignification. It is ufed indifcriminately to exprefs a fenfation of the mind, and an unknown principle, whether we call it a quality or a fubjlance, which is the exciting caufe of that fenfation. * By many ingenious philofophers, in modern times, the word Heat has been applied to the unknown principle, and has been taken in a much greater ex- tent than in common language. For, in common language, it is ufed to exprefs fuch a degree of the unknown external caufe, as will produce a given ef- fect upon the fenfes: but in the philofophical accep- tation, * See Dr. Ried's Inquiry into the Human Mind. ( 6 ) tation, it exprefles the external caufe in the abftracl, without regard to the effects which it may produce. For the fake of greater accuracy, in the following Differtation, I fhall, with the ingenious Dr. Irvine of Glafgow, call the latter abfohite heat; and what is denominated heat in common language, I fhall call fenfible heat. From this view of the matter, it appears, that ab- folute heat exprefles that power or element, which, when it is prefent to a certain degree, excites in all animals the fenfation of heat; and fenfible heat ex- prefles the fame power, confidered as relative to the effecls which it produces. Thus we fay, that two bodies have equal quanti- ties of fenfible heat, when they produce equal ef- fects upon the mercury in the thermometer ; and that the fame body has a greater or lcis degree of fenfible heat, according as is produces a greater or a lefs effect upon this fluid. But it will hereafter appear, that bodies of differ- ent kinds, have different capacities for containing heat; and, therefore, in fuch bodies, the abfolute heat will be different, though the fenfible heat be the fame. If a pound of water, for example, and a pound of antimony, have the fame temperature, we fay that their fenfible heats are equal.' "But we fhall find, that the former contains a much greater quantity of abfolute heat than the latter. Fire, in the vulgar acceptation of the word, ex- prefles a certain degree of heat, accompanied with light; and is particularly applied to that heat and light which are produced by the inflammation of combuftible bodies. But as heat, when accumulat- ed in a fuflicient quantity, is conftantly accompanied with light, or, in other words, as fire is always pro- duced by the increafe of heat, philofophers have ge- nerally confidered thefe phenomena as proceeding from (7 ) from the fame caufe; * and have, therefore, ufed the word fire to exprefs that unknown principle, which, when it is prefent to a certain degree, excites the fenfation of heat alone, but when accumulated to a greater degree, renders itfelf obvious both to the fight and touch, or produces heat, accompanied 'with light. In this fenfe, the element of fire fignifies the fame thing with abfolute heat. Thefe definitions and remarks being premifed, I fhall proceed to give the reader a concife view of the general facts upon which the experiments, 're- cited in the following pages, are founded. I. Heat is contained in great quantities in all bo- dies, when at the common temperature of the at- mofphere. In the deferts of Siberia, as we learn from Baron Demidoff, the mercury fometimes falls an hundred and fifty degrees below the freezing point. This is the mod intenfe natural cold that has ever been known. But a milch greater degree of cold has been produced by art. At Peterfburg, in the year 1759, the heat was fo much diminiflied by a mix- ture of fnow and fpirit of nitre, in the time of a fe- vere frofl, that the fpirit of wine thermometer funk to 148, and the mercurial thermometer to 352 de- grees below the beginning of Farenheit's fcale. As in this experiment the mercury was frozen, and as before its congealation, it contracted fuddenly and irregularly, it has been concluded by Dr. Black and Dr. Irvine, that the cold which was then produced, was fuch.as was indicated by the fpirit of wine ther- mometer ; and, therefore, 148 degrees below o is confidered as the freezing point of mercury. This is the greateft cold that has ever been obferved in nature; * See Boerhaave, Martin M'Q"er, Scq> ( 8 ) nature ; and yet we have no reafon to believe that the bodies which were expofed to it, were deprived of their whole heat. From thefe facts, however, we may conclude with certainty, that heat is con- tained in great quantities in all bodies, when at the common temperature of the atrnofphere. 2. Heat has a conftant tendency to diffufe itfelf over all bodies, till they are brought to the fame de- gree of fenfible heat. Thus, it is found by the thermometer, that if two bodies, of different temperatures, are mixed toge- ther, or placed contiguous, the heat pafles from the one to the other, till they both come to the fame temperature; and that all inanimate bodies, when heated, and placed in a cold medium, continually lofe heat, till, in procefs of time, they are brought to the flate of the furrounding medium. 3. If the parts of the fame homogeneous body have the fame degree of fenfible heat, the quantities of abfolute heat will be proportionable to the bulk or quantity of matter. Thus the quantity of abfo- lute heat contained in two pounds of water, muft be conceived to be double of that which is contain- ed in one pound, when at the fame temperature. This I think is evident from the fimilarity in the par- ticles of the fame homogeneous folid and fluid fub- flances. For the particles being fimilar, their pow- ers will be equal; their capacities for receiving heat will be the fame ; and therefore the quantities of ab- folute heat which they contain, will be in proportion to the bulk or quantity of matter. 4. The mercurial thermometer is an accurate meafure of the comparative quantities of abfolute heat, which are communicated to the fame homoge- neous bodies, or feparated from them, as long as fuch bodies continue in the fame form. To ( 9 ) To illuftrate this, let us fuppofe two equal parts of mercury, or of any other fluid. And let the part A be raifed to a higher temperature than the part B, A will therefore contain a greater quantity of ab- folute heat than B. Let them now be mixed ; and according to the fecond general faclj they will arrive at the fame common temperature. But they cannot come to the fame temperature, unlefs A communi- cates to B, orte half of the excefs of its heat above the original heat of B. For, let the whole heat con- At- tained in A, previous to the mix- ture, be reprefented by the fi- i -----k I - gure, a b c. And let the heat contained in B be reprefented by f g hi When they are / *— h d mixed together and brought to the fame temperature, let the heat of A be diminifhed by the figure a I m e, and iet that of B be increafed by the figure i f h k. And fince the heat which is taken from A is the very fame with that which is added to B, it is manifeft that a I m c muft be equal to i f h k. Now it is affirmed, that a I m c, or ifh k, is equal to / de m, or in other words, that A communicates to B one half of the cxcefs of its heat above the original heat of B. For from the third general fact, it is e- vident, that when A and B are brought to the fame temperature, they contain equal quantities of abfo- lute heat. Therefore the figure ig k, is equal to the figure / m b. For the fame reafon the figure f g ht is equal to the figure db e. And therefore the re- mainder ;' / h k, or a I m c, is equal to the remain- der Ide m. If, therefore, a mercurial thermometer, of the fame temperature with a quantity of water, the ab- B folute £ K 10 y folute heat of which is reprefented by d b e, be im- merfed iri the fame water, when its abfolute heat is reprefented by I b m, and be again immerfed in it, when its abfohite heat is reprefented by a b c ; and if the expanfions of the mercury be in thefe in- ftances, in the ratio of one to two, it is evident that the e::n:ipfions, and the increments of abfolute heat, will be in exact proportion. A variety of experiments were made upon this principle by Monf. De Luc, from which it appears, that the expanfions of mercury between the freezing and boiling points of water, correlpond precifely to the quantities of abfolute heat applied. The mercurial thermometer therefore is an accu- rate meafure of the comparative quantities of abfo- lute heat, which are communicated to the fame ho- mogeneous bodies, or feparated from them, as long as fuch bodies continue in the fame form. It has been already fhown, that in the fame ho- mogeneous bodies, if the quantities of matter be different, but the temperatures the fame, the quan- tities of abfolute heat will be, in proportion to the quantities of matter. It now appears, that in the fame homogeneous bodies, if the temperatures be differrnt, but the quantities of matter the fame, the quantities of ab- folute heat will be in proportion to the tempera- tures, or to the expanfions in the mercurial ther- mometer. For let the whole of the abfolute a\-----d heat contained in a pound of ice, at ' the temperature of o, the beginning e\_____ of Farenheit's fcale, be reprefented by the figure, abed, and let this heat Z>'_____1^ be disninifhed till it becomes equal to e b c /, which is the one half of a b c d. If a mer- curial thermometer were deprived of its whole heat, and / ( II ) and applied to the ice when its heat is reprefented by e b c/, and were again applied to the fame ice when its heat is reprefented by a b c d; the expanfion pro- duced by the heat e b c f would be to that produ- ced by a bed, in the ratio of one to two*. If a bed were tripple of e b c f, the expanfions would be in the ratio of one to three; and, umvcrfally, the temperatures being different, but the quantity of matter the fame, the quantities of abfolute heat will be in proportion to the temperatures, as mea- fured by the mercurial thermometer. This conclufion is an inference from De Luc's ex- periments, which prove, as was obferved above, that the expanfions of mercury are in proportion to the increafe of the abfolute heat, and its contractions to the diminution of this element, in all the interme- diate degrees, between the boiling and freezing points of water: from whence it is inferred, that if the mercury were to retain its fluid form, its con- tractions would be proportionable to the decrements of the abfolute heat, though the diminution were continued to the point of total privation. Corollary. If therefore the fenfible heat of a body, as meafured by the mercurial thermome'er, were to be diminifhed the one half, or the one third, ©r in any given proportion, the abfolute heat would be diminimed in the fame proportion. 5. The comparative quantities of abfolute heat which are communicated to different bodies, or fe- parated from them, cannot be determined in a dirtct manner by the thermometer. Thus if the tempera- ture of a pound of mercury be raifed one degree, and that of a pound of water one degree, as indi- cated by the thermometer, it docs not by any means B 2 foiiow, * It is here fuppofed that the mercury continues fluid when it is de- prived of its whole heat. :( i* ) follow, that equal quantities of abfolute heat have been communicated to the water and the mercury. It has been thought by fome philofophers, that the quantities of abfolute heat in bodies, are in pro? portion to their denfities. Boerhaave was of opini- on, that heat is equally diffufed thro' all bodies, the denfeft as well as the rareft, and therefore that the quantities of heat in bodies are in proportion to their JDUlk. But it appears from experiment, that the law of the diftribution of heat throughout the various claf- fes of natural bodies, is not according to the ratio pither of bulk or denfity. The firft attempt to determine by experiment the comparative quantities of abfolute heat in bodies, was made by Farenheit, at the defire of Boerhrave. The following is a fhort fketch of this attempt, nearly in the words of the author: If you take equal quantities of the fame fluid, and give them different degrees of heat, and mix them intimately together, the temperature of the mixture will be half the excefs of the hotter above the colder, If, for example, a pint of boiling water at 212, be mixed with a pint of the fame fluid at 32, the temperature of the mixture will be 122: the warm water will be cooled 90 degrees, and the cold water heated 90. But if this experiment be made with water and mercury, in the fame circumftances, the effect will be very different. For if you take equal bulks of mercury and wa- ter, and give the water a greater degree of heat than $he mercury, the heat of the mixture will always be greater than half the excefs of the heat of the water above that of the mercury. On ( '3 ) On the other hand, if the mercury be hotter than the water, the temperature of the mixture will con- ftantly be lefs than half the excefs of the heat of the mercury above that of the water. The changes which are produced in the temperature of the water and mercury, in the firft of thefe inftances, are found to correfpond to thofe which are produced, by mixing three parts of hot water with two of cold; and in the fecond inftance, to thofe which take place, when three parts of coid water arr mixed with two of hot. That is, the change produced in the heat of the mer- cury, is to that produced in the heat of the water, as three to two. From the former of thefe experiments it was juftly concluded by Boerhaave, that in the fame body, the diftribution pf fire is »in prgportion to the bulk or quantity of matter. But from the experiments with water and mercury, he concluded very unwarrantably, that heat is equal- ly diftufed thro* all bodies, the denfeft as well as the rareft j and therefore that the quantities of heat in different bodies, are in proportion to their bulks, or to the fpaces which they occupy. Thefe experiments have been repeated and varied in the prefent age, and very different conclufions have been drawn from them. < I have already obferved, that, if a pint of mercury at ioo, be mixed with an equal bulk of water at 50, the change produced in the heat of the mercury, will be to that produced in the heat of the water, as three to two ; from which it has been inferred, that the abfolute heat of a pint of mercury is to that of an equal bulk of water, as two to three: or, in other words, that the comparative quantities of their abfo- lute heats are reciprocally proportionable to the chan- ges ( 14 ) ges which are produced in their fenfible heats, when they are mixed together at different temperatures *. The truth of this conclufion may be illuftrated in the f^jJowing manner. If wjwpounds of diaphoretick antimony at 20, be mixed with one pound of ice at 32, the temperature of the mixture will be very nearly 26. The ice will be cooled fix degrees, and the antimony heated fix. If we reverfe the experiment, the effect will be the fame. That is, if we take fix degrees of heat from three pounds of antimony, and add it to a pound of ice, the latter will be heated fix degrees. The fame quantity of heat, therefore, which raifes a pound of ice fix degrees, will raife three pounds of antimony fix degrees, If this experiment be made at different tempera- tures, we fhall have a fimilar refult. If, for exam- pie, the antimony at 15, or at any given degree be- low the freezing point, be mixed with the ice at 32, the heat of the mixture will be half the excefs of the hotter above the colder, From hence we infer, that the refult would be the fame, if the antimony were deprived of its whole heat, and were mixed with the ice at 32. But it is evident, that, in this cafe, the ice would communicate to the antimony the half of its abfolute heatf. For, if 200 below froft, be conceived to be the point of total priva- tion, the antimony will be wholly deprived of its heat, when its temperature is diminifhed 200 degrees below 32 j and the heat contained in the ice, when at * This fatt has, for feveral years, been taught publicly by Dr. Black and Dr. Irvine, in the UnJverfities of Edinburgh and Glafgow-.- and it has been applied by Dr. Irvine, to the folution. of a variety of curious and important phenomena. It is hoped, that thofe learned and ingenious philofophers will foou favour the world with their refpe&ive discoveries in this branch of fci- ence. f See the Corollary to the 4th general fait. ( «5 ) at 3*, will be 200 degrees. If we now fuppofe them to be mixed together, the temperature of the mixture will be half the excefs of the hotter above the colder; or the ice will be cooled i©o degrees, and the antimony heated 100. The one half of the heat, therefore, which was contained in the ice, previous to the mixture, will be communicated to the antimony: from which it is manifeft, that, after the mixture, the ice and antimony muft contain e- qual quantities of abfolute heat. To place this in another light, it has been proved, that the fame quantity of heat which raifes a pound of ice fix degrees, will raife three pounds of antimo- ny fix degrees. From which it is inferred, that the fame quantity of heat which raifes the ice 200 de- grees, or any given number of degrees, will raife the antimony an equal number of degrees *. A pound of ice, therefore, and three pounds of antimony, when at the fame temperature, contain equal quantities of abfolute heat. But, it appears from the third general fact, that three pounds or an- timony contain three times as much abfolute heat, as one pound of antimony; and hence the abfolute heat of a pound of ice, is to that of a pound of antimony, as three to one. Again, if a pound of ice at 32, be mixed with a pound of antimony at 12, the temperature of the mixture will be 27; the ice will be cooled five de- grees, and the antimony heated 15; or the change produced in the fenfible heat of the ice, will be to that produced in the fenfible heat of the antimony, as one to three. But it was before proved, that the abfolute heat of a pound of ice, is to that of a pound of antimony, as four to one. From which it is evi- dent, that the comparative quantities of abfolute heat, * It is here fuppofcd, that the ice continues in the fame term. ( 16 ) in equal weights of ice and antimony, are recipro- cally proportionable to the changes which are produ- ced in their fenfible heats, when they are mixed to- gether at different temperatures ** Thus it appears, that the comparative quantities of abfolute heat in bodies may be determined, by mixing them together as above, and obferving the changes which are produced in their fenfible heats. This rule, however, does not apply to thofe fubftan- ces, which, in mixture* excite fenfible heat or cold by chymical action* From the reafoning which was employed to efta- blifli the above propofition, it follows, that equal weights of hetrogeneous fubftances, as air and wa- ter, having the fame temperature, may contain un- equal quantites of abfolute heat. There muft, there- fore, be certain effential differences in the nature of bodies, in confequence of which fame have the pow- er of collecting and retaining the element of fire, in greater quantities than others. Thefe different powers arc called in the following pages, the capaci- ties of bodies for containing heat. Thus, if we find by experiment, that a pound of water contains three times as much abfolute heat, as a pound of antimo- ny, the capacity of water for containing heat, is faid to be to that of antimony, as three to one. SECT. * I have thus endeavoured briefly to eftablifh the truth of the above doclrine, as a neceflary introduction to the experiments which follow, but the more full and complete illuftration of it I fhall leave to Dr. Black and Dr. Irvine. This difcovery opens a wide field for irtveftigation, as by means of it fceare enalled to eftimate the comparative quantities of abfolute heat ji bodies, and to determine with certainty and accuracy, the various proportions in which the element of fire is diliributed throughout the rtmorent kingdoms of Nature; ( *7 ) SECT. II. O A V IN G premifed thefe general fads, I fhall now lay before the reader my Experiments on Ani- mal Heat, and the Inflammation of Combuftiblc Bodies. * It was obferved above, that fenfible heat has a conftant tendency to diffufe itfelf equally over all bodies, till they are brought to the fame tempera- ture. From this property of heat, it is mani-eft, that thofe animals which have a higher temperature than the medium in which they live, muft be con- tinually communicating heat to the furrounding bo- dies. Since therefore, in the animal kingdom, there is a conftant diflipation of heat, it follows, that there muft be a proportionable fupply of this element, to repair the wafte. For, if the animal body had not the power of exciting or collecting heat, it would foon arrive at the temperature of the ambient me- dium. With a view to difcover the nature of this power, I made a variety of experiments, in the fummer, 1777, on animal, vegetable, and mineral fubftances; C fome * I think it proper to obferve, that I was led to the confideration of this fubjecf:, in confequence of having attended the chymical Lectures of the learned and ingenious Dr. Irvine of Glafgow. And it is a tribute of juftice which I owe to this philofopher, to acknowledge, that the fo- lution which he has given of Dr. Black's celebrated difcovery of lateat heat, or of the heat v\ hich is produced by the congelation of water, fpermaceti, bees-wax, metals, &c. fuggeited the views which gave rife to my experiments. I muft alfo add, that Dr. Irvine, from the folmion which he has given of the above phenomena, and from the general fact, that hetero- geneous bodies have different capacities for containing heat, concluded, that there was a difference between the abfolute heat of fixed and at- mofpherical air. It remained to afcertain this difference, and to deter- mine by experiments, whether fixed or atmofpherical air, contained the greater quantity of abfolute heat. ( i8 ) feme of which I fhall now relate, as I think they have led to the true fource, from whence the heat of animals, and the heat which is produced by the inflammation of combuftible bodies, is derived. I muft firft obferve, that experiments for deter- mining the comparative quantities of abfolute heat in bodies, are liable to three caufes of inaccuracy. i. "When the fubftances to be compared, are mixed together, a certain time is required for the heat to pafs from the warmer to the colder body, till they arrive at the fame temperature. If they be intimately mixed, and the veffel be a little agitated, a minute is generally fufficient. During this interval, a part of the heat is carried off by the furrounding atmof- phere. It therefore becomes neceffary, to calculate the heat which is thus loft in the firft minute. A very fimple and ingenious rule was laid down for this purpofe, by the illuftrious Sir Ifaac New- ton. Confidering the heat in a body, as the excefs whereby it is warmer than the furrounding medium, he fuppofed, that the quantities of heat loft in fmall portions of time, would always be proportionable to the heats remaining. Thus, if a body were 180 degrees hotter than the atmofphere, the quantity of heat which it would lofe in a given moment, would be double of that which it would lofe in an equal portion of time, if it were only 90 degrees hotter than the atmofphere. And, therefore, if the times be taken in arithmetical progreffion, the decrements of heat will be in geometrical progreflion. But, it has been obfrrved by Dr. Martine, that this rule is not to be admitted without foine reftriction. He has inferred from a variety of experiments, that the dif- ferential decrements are in a proportion fomewhat greater than the inherent quantities of heat; and, there- ( '9 ) therefore, that the quantities of heat loft, are part- ly equable, and partly in geometrical progreflion*. This obfervation of Dr. Martine, it mull: be allow- ed, is well founded. But when the body, which is to be the fubject of an experiment, trahfmits heat very faft, and its temperature is much greater than that of the ambient medium, the error produced, by calculating according to Sir lfaac Newton's rule, is fo very inconfiderable, that it may be neglecled. On the contrary, when the experiment is made in a veflel that tranl'mits heat very flovvly, and the heat of the fubftance to be examined is not much greater than that of the atmofphere, che quantities of heat loft in any two fmall fucceflive portions of time, approach fo nearly to an equality, that the difference cannot be diftinguifhed by the niceft ther- mometer. That this obfervation is well founded, appears from the following experiment: A pound of water in an earthen veffel, being raifed to 120, the temperature at the end of 1 minute was — — 119 2 — — — 118 3 — — ~ ll7 4 — — — 116 5 — — — 115 6 — — — 114 7 ~ — — »J3 In the experiments which I fhall hereafter relate, the order of cooling was obferved for feveral mi- nutes ; and, in general, the heat which was loft in the firft minute, was calculated according to Sir lfaac Newton's rule, from the feries of numbers determined by obfervation. I muft here obferve, that I believe Dr. Irvine was the firft who applied this rule of Sir lfaac Newton, C 2 to * See Martine's Eftys, ( ^o ) to calculate the heat loft during the firft minute, in experiments for determining the abfolute heat of bodies. 2. If, in making thefe experiments, the fubflance which has the greateft heat, be mixed with that which has the leaft, in a cold veffel, a part of the heat will be communicated to the veffel: But if the experiment be made in a warm veffel, the cold fub- ftance will receive heat, not only from the warm fubftance, but from the veffel in which it is con- tained. The moft effe&ual method of avoiding this caufe of inaccuracy, is firft to determine the capacity of the veffel for receiving heat, compared with that of one of the fubftances to be examined. The relative capacity of the veffel, in which fome of the following experiments were made, compared with that of water, were thus determined. The air in the room being — 61 A pound of water at — — 168 was poured into an earthen veffel at — 68 The temperature of the water at the end of i minute was — — - 155 2 — — — 150 .3 — — -- 145 To difcover the heat communicated to the atmof- phere in the firft minute, fay as 84 to 89 fo is 94 to a fourth proportional, which gives 99.5. From which it appears that 5.5 were carried off by the air in the firft minute, adding $.$ to 155 we have .160.5 for the true temperature of the water and of the veffel. Subtracting this from 168, we have 7.5 for the quotient. The water was therefore cooled by the veffel 7.5, and the veffel was heated by the water 92.5. And fince the veffel received this heat from the water, it is manifeft, that the fame quantity of heat, ( tl ) heat, which changes the temperature of a pound of water, 7.5 will change the temperature of the veffel 92.5. And by a parity of reafoning, the fame heat which raifes the water one degree, will raife the vef- fel i2f. If, therefore, in any experiment, we find that the veffcl has received 12I of heat from a pound of water, we may be fure that the feparation of this heat, has cooled the water one degree. 3. In experiments for determining the abfolute heat of bodies, water is generally the ftandard. When the body which is to have its heat compared with that of water, tranTurns heat very flowly, it frequently happens, that the different parts of the mixture, cannot be brought precifely to the fame temperature for fcveral minutes. Thus I find that in experiments upon vegetables and the calces of metals, there is a confiderahle difference, at the end of the firft minute, between the heat of the mixture at the furface, and that at the bottom of the veffel; arifing partly from the tendency of the warm-eft part of the water to remain at the furface, and partly from the difficulty with which the above-mentioned fubftan- ces tranfmit heat. This may be remedied in fome degree, by mixing the bodies together intimately, and agitating the mixture brifkly. But by much a- gitation, the heat is carried off fuddenly and irregu- larly, which makes it difficult to calculate the heat that is loft in the firft minute. The method which I apprehend, leaft liable to error, is to agitate the mixture moderately, and at the end of the firft minute, to take the arithmetical mean between the heat at the furface, and that at the bot- tom of the veffel; and if in a variety of experiments, in different circumftances, we find that the refult is nearly the fame, we may be fure that we have ap- proached very near the truth. ■ With • ( *» ) With thefe precautions, the following experiments were made, to determine the abfolute heat of fome of the mod common vegetable and animal fub- ftances, compared with that of water. EXPERIMENT I. Air in the room —- — 69 A pound of wheat at — 66 was mixed with a pound of water at 166 The mixture being agitated for a fhort time, The temperature at the end of furface bottom medium 1 minute was 138 — 128 — 133 2 — 134 — 125 — 1294 3 — 131 — 122 — 1264 4 — 127 — 120 — 1234 The mean temperature of the mixture at the end of one minute was 133, at the end of two minutes 1291, at the end of three minutes 1264: And there- fore the heat carried off by the air in the firft minute, being calculated according to Sir lfaac Newton's ru'e, was very nearly 3^. If we add this to 133, we fhall have 136^ for the true temperature of the mixture. It was proved that the capacity of the veffel for re- ceiving, heat, was to that of the water as 1 to 12 j. In the experiment which we are now ccnfidering, the veffel was raifed from 66 to 133, or 67.5; di- viding this by i2f, we have nearly 5.5 for the quo- tient. From which it appears, that the water was cooled by the veffel 5.5, or the veffel feparated 5.5 degrees from the water. The true temperature of the mixture was 136*, fubtracting this from 166, we have 294 for the remainder. The water was there- fore cooled 294 by the wheat andthe veffel together. But we have fhown that it was cooled 5.5 by the vef- fel ; it was therefore cooled 24 by the wheat. But the wheat was railed from 66 to 1361 or 70.5. It follows, ( *3 ) follows, that the fame quantity of heat which will change the temperature of water 24, will change that of wheat 704. Therefore the abfolute heat of water is to that of wheat, as 701 to 24, or very nearly as 2.9 to 1. EXPERIMENT II. Air in the room — __ 6o. One pound of oats, having the hulls taken off, at — — 6t, was mixed with one pound of water, at 161 ; The temperature of the mixture at the end of furface bottom medium 1 minute was 127 • — 123 — 125 2 — 125 — 122 — 1234 3 — 121 — 121 — 121^ 4 — 118 — 118* 5 — 114 — 116 6 m — 115 To 125, the mean temperature of the mixture, adding 24 for the heat carried off by the air in the firft minute, we have 1274 the true temperature of the mixture. By calculating, as in the preceding experiment, it appears that the water was cooled by the veffel nearly 5.4. The oats were raifed from 61 to 1274 or 66i; fubtracting 1274 from 161, we find that the water was cooled by the oats and the veffel tbgether 33*; but it was cooled 5.4 by the veflel ; it was therefore cooled 28.1 by the water: and hence the abfoli heat of water is to that of oats, as 66.5 to 28. , q as 2.36 to 1, that is, nearly, as i\ to 1. EXPERIMENT III. Air in the room — ^q. One pound of beans at — 60, .vas mixed with one pound of water at 160 The ( *4 ) The temperature of the mixture at the end of furface bottom medium I minute, was 119 — "3 — Il6 2 — 117 — 109 — IJ3 3 — 116 — 107 — 1114 4 — "3 — 106 — 1094 5 — 111 — 105 — 108 6 — '°9* — '°44 — 107 7 — 1074 —■ 104 — 1061 ii — 101 — IOI — IOI To 116 adding 3 degrees for the heat carried off by the air in the firft minute, we have 1 19 for the temperature of the mixture. It appears, from cal- culation, that the water was cooled by the veffel 4.8. The beans were raifed from 60 to 119, or 59 de- grees, fubtrading 119 from 160, we find that the water was cooled, by the beans and the veffel toge- ther, 41 degrees. But it was cooled by the veffel 4-8. It was therefore cooled by the beans 36.2. Ami hence the abfolute heat of water is to that of beans as 59 to 36.2, or nearly as 1.6 to 1. EXPERIMENT IV. Air — _ _ 6li A pound of barley at — __ 60 was mixed with a pound of water at 160 ; The temperature of the mixture at the end' of furface * bottom medium 1 minute was 126 — 120 __ 123 2 — 122 — 115 — H84 3 — 119 — II3 _ Il6 6 — 109 — 109 — 109 To 123, the mean temperature, adding 4.4 for the heat carried off by the air in the firft minute, we have 1274 the true temperature of the mixture. The veffel was raifed by the water 664, dividing this by i2f, we have 5.3 for the quotient j by which it appears C «s ) appears that the water was cooled by the veffel $.$. The barley was raifed from 60 to 1274 or 674. The water was cooled by the veffel and the barley toge- ther, from 160 to 1274, or 324. But it was cooled 5.3 by the veflel. It was therefore cooled 27.2 by the barley: and hence the abfolute heat of water is to that of barley as 67.5 to 27.2, or nearly as 2.4 to 1. * EXPERIMENT. V. Air — — 60. One pound of the lungs of a fheep at 59, was mixed with a pound of water at 149 ; The mixture ar the end of furface bottom medium I minute was 112 — 108 — no 2 — 109 — 106 — 1074 3 — 106 — 105 — 1054 4 — 103 — 103 — 103 Adding 2.5 for the heat carried off by the air in the firft minute, we have n 2.5 for the true temper- ature of the mixture, The veflel was raifed from 59 to n 2.5, or 53.5. Dividing this by I2f,* we have nearly 4.3 for the quotient. From which it appears, that the water was cooled by the veffel 4.3. The flefh was raifed from 59 to 112.5, or 53.5. The water was cooled by the flefh and the veffel, from 149 to 112.5, or 36.5 ; but it was cooled 4.3 by the veffel; it was, therefore, cooled 32.2 by the flefh. And hence the abfolute heat of water is to that of flefh, as 53.5 to 32.2; or, nearly as 1.3 to 1. EXPERIMENT VI. Air — # — One pound of milk at — — was mixed with a pound of water at D 60, 60. 160; The ( 26 ) The temperature at the end of furface bottom medium i minute was 109 — 107 — 108 2 — 106 — 104 — 105 3 — 103 — 10a — 102S To 108, the mean temperature, adding «.8, we have 110.8, the true temperature of the mixture. The veffel was raifed by the water 5U.8. The water was therefore cooled by the veffel 4.1.* But it was cooled by the milk and the veffel together 49.2. It was confequenijy cooled by the milk 45.1. The milk was raifed from 60 to 110.8, or 50.8. And hence the abfolute heat of water is to that of milk, as 50.8 to 45.1 ; or, nearly as 1.1 to 1. EXPERIMENT VII. Half a pound of water at — 47, was mixed with a half pound of blood at 98 ; Having agitated the veffel, the heat was in a fhort time nearly equally diffufed over the whole, and the mixture continuing fluid for the fpace of two mi- nutes, its temperature at the end of 1 minute was — 71 2 — — — 70 coagulated. 3 — — 7° 4 — — 70 5 — — — 70 6 — — 69 The blood, which was the fubject of this experi- ment, was procured from a fheep, by dividing the veins and arteries of the neck ; and appeared by its colour to be a mixture of venous and arterial blood, though confifting chiefly of the latter. The capaci- ty of thc>veffel in which this experiment was made, for containing heat, was to that of the water, as 6 to 94; or, nearly as 1 to 15.6. The ( *7 ) Ihe mixture cooled (if we except the time of its coagulation) at the rate of one degree in a minute. Adding one degree for the heat loft in the firft mi- nute, we have 72 for the heat of the mixture. The veflel was raifed by the blood, from 47 to 72, or 25 degrees. The blood was therefore cooled by the veffel nearly 1.6: it was cooled by the water and the veflel together 26 degrees. It was therefore cooled by the water 24.4. The water was railed 25 degrees. And hence ..he abfolute heat of a mixture of venous and arterial blood is to that of water, as 25 to 24.4. Thefe experiments prove, in general, that flefh, milk, and vegetables, contain lefs abfolute heat than water, and water lefs than blood. Blood, therefore, contains a greater quantity of abfolute heat, than the principles of which it is compofed. The remarkable accumulation of heat in this fluid, led me to fufpect, that it abforbs heat from the air, in the procefs of refpiration. And in this fufpicion, I was much confirmed by the following confider.a- tions : 1. Thofe animals which are furnifhed with lungs, and which continually infpire the frcfh air in great quantities, have ihe power of keeping thenifelves at, a temperature considerably higher than the furround- ing atmofphere. But animals that are not furnifhed with irefpiratory organs, are very nearly of the fame temperature with the medium in which they live. 2. Among the hot animals, thofe are the warmeft, which have the largefl refpiratory organs, and which confequently breathe the greateft quantity of air in proportion to their bulk. Thus, the refpiratory or- gans of birds, compared with their fize, are more extenfive than thofe of any other animal; and binis have the greateft degree of animal heat. D 2 3- *n ( *8 ) 3. In the fame animal, the degree of heat is in fome meafure proportionable to the quantity of air infpired in a given time. Thus, we find that animal heat is increaied by exercife, and by whatever acce- lerates refpiration. From thefe confederations, I was naturally led to a more particular examination of this fubject: the re- fult of which, is comprehended in the following pro- pofitions: PROPOSITION I. Atmofpherical air contains a greater quantity of abfolute heat, than the air which is expired from the lungs of animals; and the quantity of abfolute heat contained in any kind of air that is fit for refpiration, is very nearly in proportion to its purity, or to its power in fupporting animal life. Before I proceed to the direct proof of this propo- rtion, it is neceffary to confider the nature of the change which the air undergoes in the lungs. It is well known, that the air expired from the lungs, occafions a precipitation in lime water. A part of it, therefore, confifts of fixed air. It has been found, by Dr. Prieftley, that the refiduum of this air, is a mixture of atmofpherical, and what he has called phlo- gifticated air, a fpecies of air which occafions no pre- cipitation in lime water, but which extinguifhes flame, and is noxious to animal life. That the fixed air produced in refpiration, depends upon a change, which the atmofpherical air under- goes in the lungs, is, I think, evident, from the fol- lowing facts. Air is altered in its properties by phlogiftic pro- ceffes, and though many of thefe proceffes are total- ly different from each other, yet the change produced in the air, is in all cafes very nearly the fame. It is diminifhed in its bulk. It is rendered incapable of main- ( 29 ) maintaining flame, and of fupporting animal life. And, if we except a very few inftances, where the fixed air is abforbed, it univerfally occafions a preci- pitation in lime water. We have therefore reafon to believe, that there is no inflance of a phlogiftic pro- cefs in nature, which is not accompanied with the production of fixed air. It may be fuppofed, indeed, that this air is difchar- ged from the fubftance which furnifhes the phlogi- fton. In fome cafes, a part of the fixed air may proceed from this fource, as in various inftances of combuf- tion and putrefaction. But there are other cafes, in which we are certain, that the fixed air is derived from a change produced in the atmofpherical air. Thus, air diminifhed by the burning of alcohol and fulphur, occafions a precipitation in lime water. The fame effect is produced, when atmofpherical air is diminifhed by nitrous air, and when it is exploded with inflammable air; and yet it is not found that brimftone, alcohol, nitrous or inflammable air, contain fixed air. But Dr. Prieftley has given us the mod decifive proof of this fact, in the following experiment. Having caufed the electric fpark to pafs through a glafs tube, the lower part of which contained fome water tinged with turnfol, he obferved, that the blue colour of the liquor was, in a few minutes, changed to red, and that the included air was diminifhed in its bulk, and rendered highly noxious. He likewife obferved, that when the fpark was taken in air over lime water, the lime was precipitated*. Since, therefore, a quantity of fixed air, is, in thefe procefles, produced by a change in the atmof- pherical air, we may conclude by induction, that the * See Dr. Prieftley's experiments and obfervatiens upon air, Vol. I. ( 3" ) the fame effect is produced in every other phlogiftic procefs. Thus it appears, that in refpiration, atmofpherical air is converted into fixed and phlogiflicated air. It is therefore neceffary, in order to determine the truth of the propofition, that we fhould compare the abfolute heat of fixed and phlogiflicated air, with that of atmofpherical air. The following experiments were made to deter- mine the heat of thefe different fpecies of air. EXPERIMENT I. Air in the room — 52, A bladder containing a pint of atmofpherical air at 102, was immerfed in a pint of water at 52. The heat of the water at the end of furface bottom j 1 minute was 53 52* 2 53 524 3 S3* 53 4 . . 5tt 53i In the above experiment, the air and the water do not feem to have been brought to the fame tem- perature, till the end of 4 minutes. That this was really the cafe, is proved by the following experi- ment. EXPERIMENT IT. Air in the room 64. A pint of water was taken, the temperature of which, was 63 at the furface, and 62f at the bottom. A pint of atmofpherical air con- fined in a bladder, was raifed to 163. The bladder containing the air being immerfed in the water the heat was determined by two thermometers, one of which was placed near the furface of the water, in contact with the bladder and the other near the bot- tom. At ( 3« ) At the end of i minute the thermometer at the furface was 674, thermometer at the bottom 62* 2 minutes 65 __ 63 3 — 65 — 63* 4 — 644 ^_ 63*. 5 —• 64f — 63! In this experiment, which was made with the fame bladder that was ufed in the former, the heat of the air in the bladder near the furface, exceeded the heat of the water for feveral minutes. And hence we may perceive the reafon why, in the firft expe- riment, the temperature of the water rofe gradually at the furface and the bottom, till the end of 4 mi- nutes; for during that time, it continued to receive heat from the air which had been immerfed in it. In that experiment, the heat communicated to the water by the air, and the bladder which contained it, was i|. Of this quantity of heat, the portion which was yielded by the bladder, will be feen by the ex. periment which follows: EXPERIMENT III. A pint of water was taken at 52. The bladder having been dried and freed from air, was raifed to 102, and being immerfed in the water, the heat of the water at the end of furface bottom 1 minute was 52* 52 2 — 52* 52* We muft allow, therefore, one quarter of a degree, in the experiment in queftion, for the heat imparted by the bladder. And hence it follows, that one de- gree was communicated by the air. To difcover, from the above experiment, the ab- folute heat of atmofpherical air compared with that of water, we may confider what would have been the effect produced, if atmofpherical air contained the fame ( 3* ) fame abfolute heat with water. In that cafe, if the air were only the one hundredth part as denfe as wa- ter, and were raifed 100 degrees above the tempera- ture of the water, it would communicate to it nearly one degree of heat. If it were only the one eighth hundredth part as denfe, and were raifed 100 degrees above the heat of the water, it would communicate to it nearly the one eighth part of a degree. If it were raifed only 50 degrees above the heat of the water, it would communicate the one fixteenth part of a degree. Now, the denfity of atmofpherical air is to that of water, in a proportion fomewhat lefs than that of. 1 to 800. If, therefore, in the experiment in que- ftion, the atmofpherical air had contained the fame. abfolute heat with water, it would have communi- cated to the water, nearly the one fixtecnth part of a degree of heat. But it communicated to it one entire degree of heat. Atmofpherical air muft there- fore contain at leaft 16 times as much abfolute heat as water. Dr. Irvine has pointed out a general rule, by which the comparative quantities of abfolute heat in bodies may be eflimated, when the quantities of matter, and the changes produced in the fenfible heats, are unequal. In that cafe, the quantities of abfolute heat, are reciprocally as the changes in the fenfible heats, multiplied into the quantities of mat- ter. By the help of this rule, the ratio of the heat of atmofpherical air to that of water, may be more accurately calculated in the following manner. It is evident, that, as equal bulks of air and wa- ter were taken, if the denfities of the water and air had been equal, the abfolute heat of the air would have been to that of the water, as 1 to 49, which is ( 33 ) is the reciprocal proportion of the changes produ- ced in the fenfible heats. Again, if the changes produced in the fenfible heats had been equal, the abfolute heats would have been reciprocally as the quantities of matter. It fol- lows, that neither being equal, the abfolute heats are in the compound ratio, of the fenfible heat gain- ed by the water, to that feparated from the air, and of the quantity of water to that of the air. The experiment was made in a quart pewter veffel, the capacity of which for receiving heat was to that of the water very nearly as 1 to 16. The quantity of water was 16 ounces; and therefore, the heat re- ceived by the veffel was equal to that which would have been received by the one fixteenth part of 16 ounces, or by one ounce of water. The *vater and veflel together were confequently equal to 17 ounces of water; and the fpecific gravity of air being to that of water in the exact proportion of 1 to 862 ; it follows that the quantity of matter contained in 17 ounces of water is to that contained in a pint of air, nearly as 915 to 1. Hence the abfolute heat of air is to that of water in the compound ratio of 915 to 1, and of 1 to 49 -From which it appears, that the quantity of heat contained in the former of thefe elements, is to that contained in the latter, as 915 to 49, or nearly, as 18.6 to 1. In calculating this experiment, no allowance was made for the heat carried off by the external air; for as the temperature of the water, alter the air was immerfed in it, exceeded that of the atmof- phere, only i*, the portion of heat which was thus carried off was fo very fmall, that it may be ne- ( 34 ) I muft farther obferve, that, from the imperfec- tion of thermometers, and from the difficulty of judging by the eye of one fourth or one third of a degree, perfect accuracy in experiments of this kind is not to be expected. The experiment, however, for determining the heat of atmofpherical air, has been frequently repeat- ed—every repetition has tended to confirm the gene- ral conclufion, and from the refult of a variety of trials, I have the greateft reafon to believe that the ratio of the heat of atmofpherical air to that of water, as deduced from the above experiment, does not ex- ceed the truth. I propofe, in future, to endeavour to afcertain, with as much accuracy as poflible, the heat of the different fpecies's of air, by a greater variety of trials, and by thermometers constructed for the purpofe I next proceed to determine the heat of fixed and phlogiflicated air. EXPERIMENT IV. Air in the room 52. A pint of fixed air, extri- cated from chalk by the vitriolic acid, was confined in a bladder, and raifed to 104. A pint of water was taken at 54. The bladder containing the air being immerfed in the water, the temperature of the water at the end of furface bottom 1 minute was 54 — 54 2 54i nearly, 54$ nearly 3 54* — m 54* The bladder in which this air was contained being freed from air, and raifed 50 degrees above the tem- perature of a pint of water, communicated to the water, one fourth of a degree. This experiment, was frequently repeated with the fame refult. EXPE- ( 35 ) EXPERIMENT V. Air in the room 6y. A pint of air, elevated from rofin by heat, was confined in a bladder, and was raifed to 104. A pint of water was taken at 64. The bladder containing the air, being immerfed in the water, the temperature at the end of furface bottom 1 minute was — 644 64 2 — — 644 64 3 — — 644 64 4 —- — 64* 64* The bladder in which the air was contained, being freed from air, communicated to a pint of water in the fame circumftances, half a degree of heat. To obtain this air, a fmall quantity of rofin, was put into a gun barrel, the end of which was heated red hot. When the rofin was violently inflamed, frefh air was blown into the touch hole, and the fumes immediately beginning to iffue copioufly, a flaccid bladder was fixed upon the end of the bar- rel. The air which was thus obtained, was partly in- flammable ; when it was forced upon a candle, it burned with a pale bluifh flame. It confifted chiefly of fixed and phlogiflicated air. EXPERIMENT VI. A pint of air elevated from tallow, as in the for- mer experiment, and confined in a bladder, was railed to 113. A pint of water was taken at 63. The bladder containing the air being immerfed in the water, the temperature, at the end of E 2 1 ml- ( 3«') furface bottom i minute was 6$$ — 63 2 — 634 — 6$i 3 — 634 — 634 4 — 634 — 634 The bladder being then freed from air, and im- merfed in a pint of water, in the fame circumftan- ces, raifed the water half a degree. This air was alfo partly inflammable, but confifted chiefly of fixed and phlogiflicated air. From thefe experiments it appears, that the quan- tity of fenfible heat communicated by fixed and phlo- giflicated air, to an equal bulk of water, (the differ- ence of temperature being 50) is fo fmall, that it cannot be meafyred by the thermometer. But we have feen, that in the fame circumftances, a pint of atmofpherical air communicates "one degree of heat to a pint of water. From hence we may conclude, with certainty, that the abfolute heat of atmofphe- rical air is greater than that of fixed or phlogiflicated air. The fpecific gravity of fixed air was found by the honourable Mr. Cavendifh, to be to that of water, as 1 to 511. If, therefore, it had contained the fame abfolute heat with water, it would have communi- cated to the water nearly the eleventh part of a de- gree. If it had contained lefs abfolute heat than water, it would have communicated lefs than the eleventh part of a degree. But fuch minute varia- tions of heat cannot be diftinguifhed by the thermo- meter; and, therefore, from this experiment, we pan draw no precife conclufion, with regard to the comparative heat of water and fixed air. ^ It is well known, that a great quantity of fixed air is contained in the crude calcarious earth. Chalk and limeftone contain more than a third of their weight of this fpecies. of air. It has been proved ( 37 ) by Dr. Black, that, when thefe fubftances are de- prived of the fixed air, with which they are com- bined in their natural ftate, they are converted into quicklime ; £nd as no fenfible heat or cold is pro- duced, by the feparation of fixed from the calcari- ous earth (as I fhall afterwards endeavour to fhow,) it is poflible, by comparing the heat of the crude calcarious earth with that of quicklime, to afcertain, with accuracy, the abfolute heat of fixed air, The following experiments were made to deter- mine the heat of chalk and quicklime. EXPERIMENT VII. A pound of chalk at — 58> was mixed with a pound of water at 158; The temperature of the mixture at the end of 1 minute was — — 135, Adding one degree for the heat carried off by the air in the firft minute, we have 136 for the temperature of the mixture. The chalk was raifed from 58 to 136, or 78 de- grees. The water was cooled by the chalk and the vef- fel together 22 degrees. It was cooled nearly 2 de- grees by the veflel—it was, therefore, cooled 20 de- grees by the chalk. And hence the heat of water is to that of chalk, as 73 to 20, or as 3.9 to 1. It is to be obferved, that no fenfible heat waj produced by mixing equal parts of chalk and watei together, when they were both at 57, which wa: the temperature of the air in the room. The abfolute heat of quicklime cannot be afcer- tained with accuracy, by making water the ftandard, as thefe fubftances, when mixed together, produce much fenfible heat. For C 38 ) For this reafon, I endeavoured to determine the abfolute heat of quicklime, by mixing together e- qual quantities of chalk and quicklime at different temperatures. But, to determine, whether the ex- periment could be made with accuracy in this way, I firft made the following experiment on chalk. EXPERIMENT VIII. Air — — 64. Half a pound of powdered chalk at 64 was mixed with an equal weight powdered chalk at 164; The mixture at the end of 1 minute was — — 116 1 — — — 114 3 — — — 112 4 — — — 1114 5 — — — in 6 — — — no$ 7 — — — no* 8 — —- — no The veffel in which this experiment was made, was heated to 114, previous to the mixture. Hence it appears, that equal quantities of chalk, at different temperatures, being mixed together; the tempera- ture of the mixture, at the end of two minutes, was half the excefs of the hotter above the colder. From a variety of trials, I have found that chalk beats and cools very flowly. And this feems to have xeen the reafon, why the hot and cold chalk were lot brought to a common temperature, till the end «f the fecond minute, EXPERIMENT IX. A pound of quicklime at — 61 was mixed with a pound of chalk at 161, The ( 39 ) The mixture at the end of I minute was -- -- no 5 — — -- I IO 6 — -- — n i 7 — -- -- mi 8 — -- — I 12 9 — -- -- m 14 10 — -- -- 111 n — -- -- 1104 12 -- — — no The veffel was heated to m, previous to the mixture. In this experiment we find, that when the chalk and quicklime were mixed together, the thermome- ter at firft fell to no; afterwards it gradually rofe to 112, which it never exceeded ; the mixture then cooled at the rate of half a degree in a minute. If, therefore, we take 112 for the temperature of the mixture, we (hall probably be very near the truth. At leaft we fhall not make the heat of quick- lime greater than it really is. For tho' fome fenfi- ble heat feems to have been produced by the mix- ture, yet the whole effect, which the production of fenfible heat can have in this calculation, is to di- minifh the heat of quicklime, compared with that of chalk. Taking 112 for the common temperature, we have 49 for the heat feparated from the chalk, and 51 for that gained by the quicklime. And hence the abfolute heat of chalk is to that of quicklime as 51 to 49. That cold is not produced by the feparation of fixed air from the calcarious earth, I endeavoured to fatisfy myfelf in the following manner. If cold were produced by the feparation of thefe fubftances, heat would be produced by their union. This conclufion is not conjectural. It is founded up- on C 40 ) on an induction of facts. It is an inference drawn from what in fimilar cafes actually takes place in nature. Thus cold is produced by the evaporation of water, and heat by the condenfatio of vapour. Like effects have been obferved by the .ngenious Dr. Black, in a very great variety of natural phenomena. And as no inflance can be fhown to the contrary, we may fafely conclude, in general, that when a body produces cold in confequence of a change of form, it will produce heat when it returns to its former ftate. To difcover whether fenfible heat is produced by the union of quicklime with fixed air, I expofed an ounce and a half of quicklime at 66, to the vapour arifing from a mixture of chalk and the vitriolic acid. In a few minutes, the thermometer in the mixture rofe to 88 ; the heat of the vapour was 82 ; and the thermometer in the quicklime flood at 78. If fenfible heat had been produced, in this expe- riment, by the union of the quicklime with the fixed air, the heat of the quicklime would have been great- er than that of the vapour. I have alfo found, that no fenfible heat is produ- ced, when quicklime is precipitated from lime water, by fixed air. We may therefore conclude, with great probabili- ty, that fenfible heat is not produced by the union of fixed air with the calcarious earth. At leafl it is certain, from thefe experiments, and from a variety of phenomena, that if heat is at all produced by the combination of thefe fubftances, the quantity is fo very inconfiderable, that it cannot affect the conclu- fions, which are contained in the following pages. As heat therefore, is not produced by the union of thefe fubftances, we may conclude that cold is not produced by their feparation, and confequently dur- ing this procefs, they will not abforb heat from the furround- ( 41 ) furrounding bodies. Hence it may be inferred, that the quantity of heat contained in the earth and air when feparated, is not greater than the heat which they contained previous to their feparation. The following is a brief illuftration of the truth of this conclufion. It is found by experiment, that the fame heat which raifes the regulus of antimony one degree, will raife the calx of antimony only the one third of a de- gree. If, therefore, we fuppofe that the regulus, when at the common temperature of the atmofphere, con- tains 200 degrees of heat, and if we conceive it to be fuddenly calcined, the heat contained in the re- gulus, will raife the calx, only the one third of 200 degrees, or 66 degrees and \; the latter will therefore during the calcination abforb 133 degrees and t of heat. And hence the calx is found to con- tain three times as much abfolute heat as the regu- lus. In like manner, if the fixed air and calcarious earth when difunited, contained a greater quantity of abfolute heat than when combined, the feparation of thefe fubftances would neceffarily be attended with the abforption of heat. But we have proved that no heat is abforbed during their feparation. We may therefore conclude, that, when, a given quantity of chalk, is refolved into its principles, by convert- ing it into quicklime and fixed air, the abfolute heat of the quicklime and fixed air taken together, is not greater than the heat which was originally contained in the chalk*. F From • This conclufion is farther confirmed by the ingenious Dr. Irvine's difcoveries with regard to the caufe of the phenomena of latent heat. As thefe difcoveries, however, have not been communicated to the world, I have not taken the liberty to point out their connection with this part of my fubjcd. ( 4* ) From thefe data, the abfolute heat of fixed air compared with that of chalk, may be calculate J in in the following manner. It has been proved that the abfolute heat of chalk is to that of quicklime, as 51 to 49, or nearly as 25 is to 24. We fhall fuppofe that chalk contains one third of its weight of fixed air ; and that the abfolute heat, contained in the quicklime and fixed air which are produced by the calcination of a given quantity of chalk, is equal to that which was con- tained in the chalk, previous to its calcination. If we conceive the whole heat in the chalk divided into 25-equal parts, the heat contained in the quick- lime, after the feparation of the fixed air, will be to the original Jieat of the chalk, as 16 to 25. For if the quicklime were equal in quantity to the chalk, its heat would be to that of the chaik as 24 to 25. But as it is only equal to two thirds of the chalk, it will be as 16 to 25. And fince the heat of the quicklime and fixed air taken together, is equal to the original heat of the chalk, the heat of the fixed air will be equal to the difference between the heat of the chalk and quicklime, or it will be repre- fented by the difference between 16 and 25. That is, the heat contained in the fixed air, after the fe- paration, will be to the original heat of the chalk, as 9 to 25, the quantity of matter m the fixed air being one third of that in the chalk. And therefore tak- ing equal quantities of chalk and fixrd air, the heat of the fixed air will be to that of the chalk, as 9 multiplied by three, or as 27 to 25, or as 1 jV to one. It has been already fhown that the heat of chalk is to that of water, as 20 to 78, or as one to 3.9. But the heat of fixed air is to that of chalk as 1^ to one; therefore the heat of fixed air is to that of water, nearly as 1 to 3.6, From ( 43 ) From thefe principles, we may determine the comparative heat of fixed and atmofpherical air. The abfolute heat of atmofpherical air is to that of water, as 18.6 to one. The abfolute heat of water is to that of fixed air as ^.6 to 1. The heat of at- mofpherical air is therefore to that of fixed air, as 18.6 multiplied by ^.6 to 1 ; or very nearly as 67 to 1. EXPERIMENT X. Air in the room — — 52. Fifteen ounces of water were taken at 5 1 ; A quantity of dephlogiftieated air, equal in bulk to 10 ounces of water, was raifed to 101; The bladder containing the air bcuig immerfed in the water, and the ball of the thermometer be. ing kept in conrad with the bladder for the firft two minutes, the temperature at the end of l minute was $y, 2 — 55- The thermometer being then removed from the bladder, the water at the end of 3 minutes was 54, 4 ~ 54, 5 ~ 54, 6 — 54: And this was found to be the heat of the water, at the centre, as well as at the furface. The blad- der in which this air was contained, communicated to the water, in the fame circumftances, the one fourth of a degree, as nearly as could be judged by the eye. Fifteen ounces of water, being heated in the fame veffel, 2 degrees above the temperature of the at- mofphere, cooled, in 20 minutes, 1 degree, or 1 fourth of a degree in 5 minutes. If, therefore, we allow the heat imparted by the bladder, for that Y 2 which ( 44 ) which was carried off by the atmofphere in the firft 5 minutes, we have 3 degrees for the heat commu- nicated to the water, by the dephlogiftieated air. The fpecific gravity of dephlogiftieated air, was found, by Dr. Prieftley, to be to that of atmofphe- rical air as 187 to 185. Its fpecific gravity is con- fequently to that of water, nearly as 1 to 852. But the bulk of the water, in the above experiment, was one third greater than that of the air. Since, therefore, if equal bulks had been taken, the wa- ter would have been to the air as 852 to 1 ; it fol- lows, that as the water was one third greater in. bulk than the air, the quantities of matter were as 1278 to 1, The heat received by the veffel was e- qual to that which would have been received by one ounce of water. The water and veffel together were therefore equal to 16 ounces of water ; and the quantity of matter in 16 ounces of water being to that contained in 10 ounce meafures of dephlo- giftieated air, as 1363 to 1, it follows, that the ab- folute heat of dephlogiftieated air, is to that of wa- ter in the compound ratio of 1363 to 1, and of 3 to 47, or, as 87 to 1. To obtain this air, a quantity of red lead was; moiftened with yellow fpirit of nitre, and the fait being dried and put into a glafs veffcl, the air was feparated by an intenfe heat, and caught in bladders. It appeared to be of a very pure kind, as a candle burned in it with a crackling noife, and with a bright and vivid flame. From this experiment, compared with experiment the 1 ft, it appears, that the abfolute heat of dephlo- giftieated air, is to that of atmofpherical air, as 87 to 18.6, or nearly as 4.6 to 1. And Dr. Prieftley, whofe difcoveries on this fubjed are defervedly much admired, has proved that its power in fupport- ( 45 ) ing animal life, is 5 times as great as that of atmof- pherical air. We have, therefore, upon the whole, fufficient evidence for concluding, that atmofpherical air con- tains a greater quantity of abfolute heat, than the air which is expired from the lungs of animals ; and that the quantity of abfolute heat contained in any Jtind of air that is fit for refpiration, is very nearly in proportion to its purity, or to its power in fup- porting animal life. PROPOSITION II. THE blood which paffes from the lungs to the heart, by the pulmonary vein, contains more abfo- lute heat, than that which paffes from the heart to the lungs, by the pulmonary artery. As the former is the blood which is returned by the veins in the aortic fyftem, and the latter is that, which, in the fame fyflem, is propelled into the ar- teries, I fhall call the firft venous, and the laft ar- terial blood. The following experiments were made to deter- mine the heat of venous and arterial blood. EXPERIMENT I. Air in the room — — "° Half a pound of water, averdupoife weight, at — — — S3* was mixed with half a pound and 400 grains of arterial blood at — l02' The mixture at the end of 1 minute was 78, 2 — 77* nearly, 2 — 774 when it coagulated, 4 """ 77h EXPE- ( 4°~ ) EXPERIMENT II. Half a pound of water, averdupoife weight, at > — — 534 was mixed with nine ounces and a half, and 14 grains of venous blood, at 99-j- The mixture at the end of 1 minute was 76, 34 — y6 when it coagulated, 8 — 76, 9 — . 751- . In making thefe experiments, it was neceffary to ule as much expedition as poflible, that the heat of the mixture might be determined previous to the coagulation ; and, therefore, the water was firft ac- curately weighed.—Half a pint of blood was taken from the carotid artery of a fheep, for the firft expe- riment, and from the jugular vein for the fecond: the heat of the mixture was then afcertained by the thermometer, and the weight of the blood was de- termined at the conclufion of the experiment. We learn from thefe experiments, that the fpecific gravity of venous blood is greater than that of the arterial. For the meafures were nearly equal, and the weight of the former was found confiderably to exceed that of the latter. The arterial blood appear- ed alfo to be much more fluid than the venous; and we have feen, that when they were mixed with equal quantities of water, the venous blood was fomewhat Uter in coagulating, than .he arterial. To determine the heat of arterial blood, from the former of the above experiments, we may obferve, that as, in this experiment, the blood was poured upon the water, a fmall portion of heat was loft in its paffage through the air. I have found by a fub- fequent trial, that the quantity of heat which was thus loft, was very nearly one degree. If this heat had been added to the mixture, it would have raifed it ( 47 ) it nearly half a degree; and as the mixture, previous to its coagulation, cooled at the rate of one fourth of a degree in a minute, we may add, at leaft, half a degree for the heat loft in the firft minute; which gives 784 for the temperature of the mixture. This experiment was made in a pint pewter veffel, the capacity of which, for receiving heat, was to that of the water, nearly as 16 to 1. The quantity of water was eight ounces ; the heat received by the veffel, was confequently equal to that which would have been received by the one-fixteenth part of eight ounces, or by half an ounce of water. It follows, that the effed of the veffcl and the water together, was equal to that which would have been produced by eight ounces and a half of water. The temperature of the mixture was 784: fub- trading this from 102, we have 234 for the heat fe- parated from the blood. The water and the veflel were raifed from 53 to 784, or 25J. The quantity of blood was eight ounces and 400 grains averdu- poife, or 3899 grains. The water and the veffel to- gether were equal to eight ounces and a half of wa- ter, or to 3717 grains. And, therefore, the heat of arterial blood is to that of water, in the compound ratio of eight ounces and a half to eight ounces and 400 grains, and of twenty-five and a half to twenty- three and a half, or as 103 to 100; confequently the heat of water is to that of arterial blood, as too to 103, or nearly as 97.08 to 100. In the fecond experiment, adding half a degree for the heat loft in the firft minute, we have 764 for the temperature of the mixture. The blood was cooled from 99! to y6h or nearly 22.83. r^e water and veflel were raifed from 534 to y6i, or 23 degrees. The quantity of venous blood was 94 ounces and 14 grains averdupoife, or 4168 grains. The water and veffel were together equal ( 48 ) equal to 84 ounces of water. Therefore the heat * of venous blood is to that of water, in the com- pound ratio of 84 ounces to 94 ounces and 14 grains, and of 22.83 t0 23» or as IO° t0 ll2m Putting A for arterial blood, V for venous, and W for water, the ratio of the heat of venous to that of arterial blood, is determined in the follow- ing manner : V. W. A. 97.08 100 112. Therefore V: A:: 9*7.08 : 112, or nearly as 10 to 114. Thus it appears, that the blood which paffes from the heart to the lungs, by the pulmonary ar- tery, contains lefs abfolute heat than that which paf- fes from the lungs to the heart by the pulmonary vein. PROPOSITION III. THE capacities of bodies for containing heat, arc diminifhed by the addition of phlogifton, and in- creafed by the feparation of this principle. As bodies, when inflamed, appear to emit light, and give out heat, from an internal fource, and as thofe bodies only are combuftible, which contain the phlogifton in a confiderable quantity, it has been an opinon generally received among philofophers, that this principle is either fire itfelf, or intimately con- neded with the produdion of fire. If this were true, bodies, when united with phlogifton, would contain a greater quantity of fire, or of abfolute heat, than when feparated from it: metals would contain more abfolute heat than their calces ; and fulphur more than the vitriolic acid. But that the contrary is the fad, as ftated in the above propo- rtion, appears from the following experiments. EXPE- ( 49 ) EXPERIMENT I. Air in the room — 64. Half a pound of water at — 62, was mixed with half a pound of tin at 162 ; The mixture at the end of furface bottom 1 minute was 68 — 68, 2 — 68 — 68. EXPERIMENT II. Half a pound of water at — 62, was mixed with half a pound cf the grey calx of tin at — — 162; The mixture at the end of furface bottom medium 1 minute was 68 — 72 — 70, 2 — 68* — 70 — 69J-, 3 — 684 — 694 — 69, 4 -r— 69 -- 69 — 69. Thefe experiments were made in a pewter veffel, the capacity of which, for receiving heat, was de- termined thus: Half a pound of water at — 160, was poured into the veffel at — 60 ; The temperature of the water at the end of 1 minute was — 150$ 2 — —- 146, 3 — — 142. Adding four degrees for the heat carried off by the air in the firft minute, wc have 154 for the Common temperature of the water and the veffel. The abfolute heat of the veffel, therefore, is to that of the water, as 6 to 94, or as 1 to 15^. That is, the heat contained in the veffel, was equal to the heat contained in the rV» part of eight ounces of wa- iter. Or nearly equal to the heat contained in half an ounce of water. G In ( 50 ) In the firft experiment, the tin was cooled 94 de- grees, and the water heated 6. Since, therefore, the tin heated eight ounces of water, and the veflel which was equal to half an ounce of water, fix de- grees, it follows, that it would have heated eight ounces and a half of water fix degrees. And hence the abfolute heat of tin is to that of water, in the compound ratio of 6 to 94, and of 8.5 to 8, or as 1 to 14.7. In this calculation, no allowance has been made for the heat which was loft in the firft minute. For, though a portion of heat muft have been feparated from the tin by ihe air, when it was mixed with the water, yet the quantity was fo very fmall, that it may be negleded. If one degree of heat were thus feparated, it would not have railed the mixture more than one-fourteenth part of a degree. And it ap- pears, that, after the tin and water were brought to a common temperature, the mixture cooled fo very flowly, that the heat which was loft, could not be meafured by the thermometer. If, however, we were to add one-fourth of a degree for the heat im- parted to the air in the firlt minute, the abfolute heat of tin would be to that of water, nearly as 1 to 14.1. In the fecond experiment, the mean temperature of the mixture, at the end of one minute, was 70. It cooled nearly at the rate of one-fourth of a degree in a minute. Adding therefore one-fourth of a de- gree for the heat loft in the firft minute, we have 8j for the heat communicated to the water and the veffel, and 914 for that feparated from the calx. But the quantity of the calx was eight ounces. The water and the veffel were together equal to eight ounces and a half of water; and, therefore, the heat of the calx, is to that of water, in the com- pound ratio of 8.25 to 91.75, and of 8.5 to 8, or as ( 5i ) as i to 10.4. Hence the abfolute heat of the calx of tin is to that of tin, as 14.7 to 10.4. EXPERIMENT III. A quarter of a pound of water at — $$, was mixed with a quarter of a pound of calx of iron at — — — ,5$. The mixture at the end pf furface bottom medium I minute was 75 — 77 rr- ^y6, 2 — 72 — 76 — 74, 3 — 71 — 74 Tr 734 4 — 71* T 724 — 72, 5 — 714 — 7'f — 7H- During five minutes, the mixture cooled nearly at the rate of a degree in a minute. Adding one degree for the heat loft in the firft minute, yte have 77 for the mean temperature of the mixture. The water, therefore, was heated 22 .de- grees, and the calx cooled 78. The quantity of the calx was four ounces. The water and the veffel together were equal to four ounces and a half of water. And, hence, the beat of the calx is to that of waiter, hi the compound ratio of 22 to 78, and of 4.5 to 4 ; or, nearly as 1 to 3.1. The heat of iron was found, by Dr. Black, and Dr. Irvine, to be to that of water, as one to eight. I have fince repeated this experiment with nearly the fame refult*. It appears, therefore, that the abfolute heat of the calx of iron is to that of the metal, as 8 to 3.1. G 2 EXPE- # I muft farther obferve, that, before I made the experiment; which are recited in this fection, the heat of lead and tin, in wi; r ;u?rGi;c ftate, had alio been determined by the above mentioned pluloiu^nt.-rs. ( 52 ) EXPERIMENT IV. Air in the room — —■ Half a pound of water — was mixed with half a pound of lead The mixture at the end of furface bottom I minute was 624 — 624, 2 — 624 —- 624. EXPERIMENT V. Air in the room — — 61, One half pound of water — 60, was mixed with half a pound of red lead 160; The mixture at the end of furface bottom medium 1 minute, was 644 — 6y — 65^, 1 — 644 — 664 — 654, 3 — 65 — 66 — 654, 4 — 6$ — 65i — 65\, 5 — 644 — 644 — 644. The heat received by the veffel, in the fourth ex- periment, was equal to that which would have been received by one half ounce of water. The quantity of water was eight ounces. The water and the vef- fel together were equal to eight and a half ounces of water : and, therefore, the quantity of lead be- ing eight ounces, the abfolute heat of lead is to that of water, in the compound ratio of 4.5 to 95.5, and of 8.5 to 8, or nearly as 1 to 19.9. In experiment fifth, the mean temperature of the mixture, at the end of one minute, was 6£. Du- ring five minutes, it cooled nearly at the rate of one fourth of a degree in a minute. Adding, therefore, one fourth of a degree for the heat loft in the firft minute, we have 66 for the temperature of the mixture. The 61, 58, 158; ( 53 ) The calx was cooled 94 ; the water and the vef- fel were heated 6 ; and hence the abfolute heat of the calx is to that of water, in the compound ratio of 6 to 94, and of 8.5 to 8, or as 1 to 14.7. It follows, that the abfolute heat of the calx is to that of lead, as 19.9, to 14.7. EXPERIMENT VI. Air in the room — — 58. One fourth of a pound of water at 59, was mix- ed with one fourth of a pound of a compound, confifting of equal parts of the calces of lead and tin, at 159. The mixture at the end of furface 1 minute was ^5 a — 3 — 4 — ^3 64 66 5 — 6 — 65 65 >ottom medium 69 - 67, 6y - &5h 66 — (>5> 65* - &5h <>5i - 65!, 65 - 65- mixture, at the end The mean temperature of the mixture, of one minute, was 6y. It cooled two degrees in fix minutes; adding therefore, one third of a degree for the heat loft in the firft minute, we have 677, or 67.3, nearly for the true temperature of the mixture. The calx was cooled 91.7. The water heated 8.3. The abfolute heat of the calx therefore is to that of water, in the compound ratio, of 8,3 to 91.7, and of 4.5 to 4, or as 1 to 9.8. It is to be obferved that thefe metals calcine more perfedly when mixed, than when feparate. EXPERIMENT VII. Air — — — 64, Half a pound of water at — 6^, was mixed with half a pound of the regulus of antimony at 163, The ( 54 ) The mixture at the end of i minute was at the furface and bottom 70, 2 — — — 684. 3 — — — 68. EXPERIMENT VIII. Air — — 6r, One fourth of a pound of water at 58^ was mixed with one fourth of a pound of calx of antimony at 158** The mixture at the end of furface bottom medium 1 minute was 724 — yy — 74 2 — 7H — 744 — 73 3 — 71 — 72 — 71. 4 — 701 — 71 — yol. In Experiment VII. the mixture cooled at the rate of half a degree in a minute. The water and veffel were heated 7.5. The regulus was cooled 92.5. The heat of the regulus, therefore, is to that of water in the compound ratio, of 7.5 to 92.5, and of 8.5 to 8, or nearly as 1 to 11.6. In Experiment VIII. the mean temperature of the mixture was 743. It cooled in 4 minutes, nearly at the rate of one degree in a minute. Adding therefore one degree for the heat loft in the firft minute, we have y^ for the true tem- perature ; confequently the abfolute heat of the calx of antimony, is to that of water in the compound ratio of 174 to 821, and of 84 to 8, or nearly as 1 to 4.5, and hence the abfolute heat of the calx of anti- mony, is to that of the regulus, as 11.6 to 4.5. By fimilar experiments, it may be demonitrated, that the vitriol.c acid contains more abfolute heat than ful- phur. We may therefore conclude, in general, that bodies, when joined to phlogifton, contain lefs abfo- lute heat than when feparated from it; and confe- quently, that, in the former cafe their capacities for contain- ( 55 ) containing heat are diminifhed, and in the latter, in- creased. It follows, that if phlogifton be added to a body, a quantity of the abfolute heat of that body will be extricated ; and if the phlogifton be feparated again, an equal quantity of heat will be abforbed. The calx of antimony, for example, contains nearly three times as much abfolute heat as the regulus: when, therefore, by the addition of phlogifton, the calx is revived, it will lofe two thirds of its abfolute heat, and, on the contrary, when the regulus is by calcination deprived of its phlogifton, the calx will recover the heat which it had formerly loft. In this point of view, the feparation of heat from a body, by means of phlogifton, and the reabforption of it, when the phlogifton is again difengaged, fcems to be analogous to the feparation of air from earths and alkali's, by means of an acid, and the reuni- on of thefe fubftances with this element, when the acid is feparated. If the vitriolic acid, for inftance, be added to a mild ajkali, the fixed air will be extrica- ted, and will fly off in the form of an elaftic vapour ; if phlogifton be added to a metallic earth, a portion of the abfolute heat will be feparated, and will fly off in the form of fenfible heat; when the acid is again feparated from the alkali, the latter recovers the air which it had loft, and when the phlogifton is again difengaged from the metallic earth, the earth reabforbs the heat which had formerly efcaped from it. Heat, therfore, and phlogifton, appear to be two oppofite principles in nature. By the adion of heat upon bodies, the force of their attradion to phlogi- fton is diminifhed ; and by the adion of phlogi- fton, a part of the abfolute heat, which exifts in all bodies as an elementary principle, is expelled. SECT. ( 56 ) SECT. III. Jt; R OM the fads which have been eftablifhed by the above experiments, the following explanation may be given of animal heat, and of the heat which is produced by the inflammation of combuftible bo- dies. I. Of Animal Heat. It has been proved, that the air which is expired from the lungs of animals, contains lefs abfolute heat than that which is inhaled in infpiration. It has been fhown, particularly, that, in the procefs of refpiration, atmofpherical air is converted into fixed air ; and that the abfolute heat of the former is to that of the latter, as 67 to 1. Since, therefore, the fixed air which is exhaled by expiration, is found to contain only the one fix- ty-feventh part of the heat which was contained in the atmofpherical air, previous to infpiration, it fol- lows, that the latter muft neceffarily depofit a very great proportion of its abfolute heat in the lungs. It has moreover been fhown, that the abfolute heat of florid arterial blood, is to that of venous, as 117 to 10. And hence, as the blood which is returned by the pulmonary vein to the heart, has the quanti- ty of its abfolute heat increafed, it is evident that it muft have acquired this heat in its paffage thro' the lungs. We may conclude, therefore, that, in the procefs of refpiration, a quantity of abfolute heat is feparated from the air and abforbed by the blood. That heat is feparated from the air in refpiration, is farther confirmed by Experiment X. Prop. I. from which experiment, compared with Dr. Prieft- ley's difcoveries, it is manifeft, that the power of any fpecies of air in fupporting animal life, is nearly in ( 57 ) in proportion to the quantity of abfolute heat which it contains, and is confequently proportionable to the quantity which it is capable of depofiting in the lungs. The truth of this conclufion, will perhaps appear in a clearer light, from the following calculation, by which we may form fome idea of the quantity of heat yielded by atmofpherical air, when it is con- verted into fixed air, and alfo of that which is ab- forbed, during the converfion of venous into arteri- al blood. We have feen that the fame heat, which raifes atmofpherical air one degree, will raife fixed air nearly 6y degrees. And, confequently, that the fame heat, which raifes atmofpherical air any given number of degrees, will raife fixed air the lame number of degrees, multiplied by 6y. In the Pe- terfburgh experiment, the heat was diminifhed 200 degrees below the common temperature of the at- mofphere. We are, therefore, certain that atmof- pherical air, when at the common temperature of the atmofphere, contains at leaft 200 degrees of heat. Hence, if a certain quantity of atmolphcrical eir, not in contad with any body that would imme- diately carry off the heat, fhould fuddenly be con- verted into fixed air, the heat which was contained in the former, would raife the latter 200 degrees multiplied by 6y, or 13400 degrees. And the heat of red hot iron being 1050, it follows, that the quantity of heat, which is yielded by atmofpherical air, when it is converted into fixed air, is fuch, (if it 'were not diflipatedj as would raife the air fo changed to more than 12 times the heat of red hot iron. . . If, therefore, the abfolute heat which is difenga- ged from the air in refpiration, were not abforbed by 6 H the ( 58 ) the Wood, a very great degree of fenfible heat would be produced in the lungs. Again, it has been proved, that the fame heat which raifes venous blood 115 degrees, will raife arterial only 100 degrees ; and, confequently, that the fame heat, which raifes venous blood any given nu iiber of degrees, will raife arterial, a lefs num- ber, in the proportion of 100 to 115, or 20 to 23. Bit we know that venous blood contains at leaft 230 degrees of heat. Htnce, if a certain quantity of venous biood, not in contad with any body that would immediately fupply it with heat, fhould fuddcnly be converted into arterial, the heat which was contained in the former would raife the latter only -*-| of 230 degrees, or 200 degrees; and con- fequenrly the fenfibie heat would fuffer a diminution, equal to the difference between 230 and 200, or 30 degree?. But the common temperature of blood is 96 ; when, therefore, venous blood is converted in- to arterial in the lungs, if it were not fupplied by the air, with a quantity of heat proportionable to the change which it undergoes, its fenfible heat would be diminifhed 30 degrees, or it would fall from 96 to 66. That a quantity of heat is detached from the air and communicated to the blood in refpiration, is moreover fupported by the experiments which have been brought in proof of the third Propofition; from which it appears, that, when bodies are joined to phlogifton, they lofe a portion of their abfolute heat, and that when the phlogifton is again difen- gaged, they reabforb an equal portion of heat, from the furrounding bodies. Now it has been demonftrated, by Dr. Prieftley, that, in refpiration, phlogifton is feparated from the b'ood and combined with the air. During this pro- cefs, therefore, a quantity of abfolute heat muft necef- C 59 ) neceffarily be difengaged from the air, by the adion of - phlogifton ; the blood, at the fame moment, being left at liberty to unite with that portion of heat, which the air had depofited, And hence animal heat feems to depend upon a procefs, fimilar to a chemical eledive attradion. The air is received into the lungs, containing a great quantity of abfolute heat, The blood is returned from the extremities, highly impregnated with phlo- gifton. The attradion of the air to phlogifton, is greater than that of the blood. This principle will, therefore, leave the blood to combine with the air. By the addition of the phlogifton, the air is obliged to depofit a part of its abfolute heat ; and as the capacity of the blood is at the fame moment increaf. ed by the feparation of the phlogifton, it will in- ftantly unite with that portion of heat which had been detached from the air. We learn from Dr. Prieftley's experiments, with refped to refpiration, that arterial blood has a ftrong attradion to phlogifton: It will confequently, during the circulation, imbibe this principle from thofe parts which retain it with leaft force, or from the putrefcent parts of the iyftem : And hence the ve- nous blood, when it returns to the lungs, is found to be highly impregnated with phlogifton. By this impregnation, its capacity for containing heat is di- minifhed. In proportion, therefore, as the blood which had been dephlogiftieated by the procefs of refpiration, becomes again combined wiih phlogi- fton, in the courfe of the circulation, it will gradu- ally give out that heat which it had received in the lungs, and diffufe it over the whole fyftem. Thus it appears, that, in refpiration, the blood is continually difcharging phlogifton and aLnorbing heat; and that in the courfe of the circulation, it H 2 is ( «o ) is continually imbibing phlogifton and emitting beat. It may be proper to add, that, as the blood by its impregnation with phlogifton, has its capacity for containing heat diminifhed ; fo, on the contrary, thofe parts of the fyftem from which it receives this principle, will have their capacity for containing heat increafed, and will confequently abforb heat. Now, if the changes in the capacities, and the quantities of matter changed in a given time were fuch, that the whole of the abfolute heat feparated from the blood were abforbed, it is manifeft, that no part of the heat, which is received in the lungs, would become fenfible in the courfe of the circu- lation. That this, however, is not the cafe, will, I think, be evident, from the following confederations. We know that fenfible heat is produced by the circulation of the blood ; and we have proved by experiment, that a quantity of abfolute heat is com- municated to that fluid in the lungs, and is again difengaged from it, in its progrefs thro' the fyftem. If, therefore, the whole of the abfolute heat, which is feparated from the blood, were abforbed by thofe parts of the fyftem from which it receives the phlo- gifton, it would be neceffary to have recourfe to fome other caufe, to account for the fenfible heat which is produced in the circulation. But, by the rules of philofophifing, we are to admit no more caufes of natural things, than fuch as are both true, and fufficient to explain the appearances; for nature delights in fimplicity, and affeds not the pomp of fuperfluous caufes*. We may, therefore, fafely conclude, that the ab- folute heat which is feparated from the air in refpira- tion. » See Newton's Principia b. iii. p. 202. ( 61 ) tion, and abforbed by the blood, is the true caufe of animal heat. It muft neverthelefs be granted, that thofe parts of the fyftem which communicate phlogifton to the blood, will have their capacity for containing heat increafed ; and therefore, that a part of the abfolute heat which is feparated from the blood will be ab- iorbed. But from the quantity of heat, which becomes fenfible in the courfe of the circulation, it is mani- feft that the portion of heat which is thus abforbed, is very inconfiderable. It appears, therefore, that the blood, in its pro- grefs thro* the fyftem, gives out the heat which it had received from the air in the lungs; a fmall por- tion of this heat is abforbed by thofe particles which impart the phlogifton to the blood; the reft becomes redundant, or is converted into moving and fenfible heat. I fhall hereafter fhow, that the heat which is pro- duced by this procefs, is fimilar io that which is pro- duced by the inflammation of combuftible bodies, with this difference, that, in the latter inftance, the fire is feparated from the air, in the former, from the blood. Of the Inflammation of combuflible Bodies. From the above experiments we learn, that at- mofpherical air contains much abfolute heat; that when it is converted into fixed and phlogiflicated air, the greater part of this heat is detached ; and that the capacities of bodies for containing heat, are di- minifhed by the addition of phlogifton, and increaf- ed by the feparation of it. From hence we infer, that the heat which is produced by combuftion, is derived from the air, and not from the inflammable body. For ( 62 ) For inflammable bodies abound with phlogifton, and contain little abfolute heat; atmofpherical air, on the contrary, abounds with abfolute heat, and contains little phlogifton. In the procefs of inflam- mation, the phlogifton is feparated from the inflam- mable body, and combined with the air; the air is converted into fixed and phlogiflicated air, and at the fame time gives off a very great proportion of its abfolute heat, which, when extricated fuddenly, burfts forth into fl.ime, and produces an intenfe de- gree of fenfible heat. We have found by calcula- tion, that the heat which is produced by the conver- sion of atmofpherical into fixed air, is fuch, if it were not diflipated, as would be fufficient to raife the air fo changed, to more than twelve times the heat of red hot iron. It appears, therefore, that in the procefs of inflammation, a very great quantity of heat is derived from the air. It is manifeft on the contrary, that no part of the heat, can be derived from the combuftible body. For the combuftible body during the inflammation, being deprived of its phlogifton, undergoes a change fimi- lar to that which is produced in the blood, by the procefs of refpiration; in confequence of which, its capacity for containing heat is increafed. It, there- fore, will not give off any part of its abfolute heat, but, like the blood in its paffage thro' the lungs, it will abforb heat. The calx of iron, for example, is found to con- tain more than twice as much abfolute heat, as the iron in its metallic form ; from which it follows, that, in the procefs of inflammation, the former muft neceffarily abforb a auantity of heat, equal to the excefs of its heat above that of the latter. Now, from whence does it receive this heat ? It cannot re- ceive it from the iron. For the quantity of heat in ( «3 ) the calx, is more than double of that which was con- tained in the iron, previous to the calcination. But in the burning of iron, the phlogifton is fe- parated from the metal, and combined with the air; and it has been proved, that, by the combination of phlogifton with air, a very intenfe heat is produced. From hence it is manifeft, that, in the inflammation of iron, the atmofpherical air is decompofed, a very great proportion of its abfolute heat is feparated, part of which is abforbed by the calx, and the reft ap- pears in the form of flame, or becomes moving and fenfible heat. We may conclude, therefore, that the fenfible heat which is excited in combuftion, depends upon the feparation of abfolute heat from the air by the adion of phlogifton. In confirmation of this conclufion, it may be pro- per to add, that, (if we except the change that the air undergoes in the procefs of refpiration, in which the heat is abforbed) the fudden converfion of at- mofpherical, into fixed and phlogiflicated air, is in- variably accompanied with the produdion of fenfible heat. Thus fenfible heat is produced when common air is mixed with nitrous air, when it is exploded with inflammable air, when it is diminifhed and ren- dered noxious, by putrefadion, by combuftion, and by the eledric fpark. If the quantity of air which is changed, by thefe proceffes, in a given time, be very great, the change is attended with much ii;;ht, with a vivid flame, and with ijntenfe heat; but if the alteration in the air be flow and gradual, the heat paffes off imperceptibly to the furrounding bo- dies. It appears, upon the whole, that atmofpherical air contains, in its compofition, a great quantity of fire or of abfolute heat. By the feparation of a portion of this fire in the lungs, it fupports the tem- perature C 64 ) perature of the arterial blood, and this communi- cates that pabulum vita, which is fo effential to the preservation of the animal kingdom. And, finally, by a fimilar procefs, it maintains thofe natural and artificial fires, which are excited by the inflammation of combuftible bodies. Affuming this dodrine as true, I (lull next endea- vour to fhew, that it affords an eafy folution of the moft remarkable fads, relating to animal heat and combuftion. . SECT. IV. Of the principal Facls relating to Animal Heat. 1. IHE above dodrine explains the reafon why the breathing animals have a higher temperature than thofe which are not furnifhed with refpiratory organs; for it has been proved that the former are continu- ally abforbing heat from the air : And, it is proba- ble, that, to provide an apparatus for the abforption of heat, was the chief purpofe of nature, in giving to fo great a part of theanimal creation, a pulmo- nary fyftem, and a double circulation. We have fhown that animal heat, and the inflam- mation of combuftible bodies, depend upon the fame caufe, that is, upon the feparation of abfolute heat from the air, by the adion of phlogiffon. The quantity of air phlogiflicated by a man in a minute, is found, by experiment, to be equal to that which is phlogiflicated by a candle, in the fame fpacc of time. And hence a man is continually deriving as much heat from the air, as is produced by the burning of a candle. It is remarked by naturalifts, that the cold animals have alfo the power of keeping themfelves at a tem- perature, ( 65 ) perature, fomewhat higher than the furrounding medium. To account for this, we may obferve, that animal heat depends, indiredly, upon a change produced in the air by refpiration, and diredly upon a change which the blood undergoes in the courfe of the circulation. In confequence of the tendency of the fyftem to putrefadion, the blood is impregnated with phlogi- fton, and by this impregnation is obliged to give out a part of its abfolute heat. The fource from which it is again fupplied with heat, in fuch of the cold animals as are not furnifhed with lungs, can only be determined by experiment. It is probable, that, in thofe animals, the aliment contains more abfolute heat than the blood. If this be the cafe, the blood will be fupplied with heat from the ali- ment. 2. From the experiments in heated rooms, it ap- pears, that the animal body has, in certain fixa- tions, the power of producing cold, or of keeping itfelf at a lower temperature than the furrounding medium. This power has been attributed by fome philofo- phers to the evaporation from the furface of the bo- dy ; and indeed it muft be allowed, that the increaf- ed evaporation, will have a very considerable influ- ence in diminifhing the heat. But the experiments, which have been related above, point out another caufe, which, I apprehend, confpires in producing the fame effed. By the heat of the furrounding medium, the eva- poration from the lungs is increafed. Now it may be fhown, that if the evaporation from the lungs be increafed to a certain degree, the whole heat which is feparated from the air, will be abforbed by the aqueous vapour. n r I From ( 66 ) From the calculation in Sed. III. page 58, it appears, that the capacity of the blood for contain- ing heat, is 10 much increafed in the lungs, that if its temperature were not fupported by the beat which is feparated from the air, in the procefs of re- fpiration, it would fall fron 96 to 66. Hence if the evaporation from the lungs be increafed to fuch a degree, as to carry off the whole of the heat that is detached from the air, the arterial blood, when it returns by the pulmonary vein, will have its fenfible heat greatly diminifhed, and will, confequently, ab- forb heat from the veffels which are in contad with it, and from the parts adjacent. And thus the very fame procefs which formerly fupplied the animal with heat, vill now become the inftrument of producing cold, and the quantity of cold produced, will be in proportion to the velocity of the blood through the lungs and the fulnefs and frequency of the refpi- ration. Hence alio we may perceive the reafon, why the heat of animals is nearly the fame, in all parts of the earth, notwithftanding the very great variations in the heat of the atmofphere, arifing from the vi- ciflitudes of the weather, and the difference of fea- fon and climate. The quantities of heat loft by bodies, when heat- ed and placed in the cold air, are in proportion to the excefs of their fenfible heat, above that of the furrounding atmofphere. Ihe heat of the human body is very nearly, at all feafons of the year, 96; and, confequently, other circumftances continuing the fame, the quantity of heat loft in a given time, when the air is at 36, will greatly exceed that which is loft in an equal portion of time, when it is at 66. It is therefore, neceffary, that, in the former cafe, a greater quantity of heat fhou'd be abforbed from the air to fupply the wafte. ( 67 ) To account for this, we may obferve, that, by the tonic and ftimulant powers of cold, the vigour of the animal body is increafed. The veffels on the furface ate conftrided. The blood is determin- ed to the lungs. The pulfe and the refpiration are rendered full and frequent. And hence, as the cold advances in winter feafons, and in northern climates, the quantity of heat abforbed from the air is proportionably increafed. In fummer, the blood is determined to the fur- face, the velocity of the circulation through the lungs, is diminifhed, and hence, a proportionable diminution in the quantity of heat abforbed. We may add to this, that, if the quantity of heat ab- forbed by the vapour, which is exhaled in refpira- tion, be fo great, as that the remaining portion of the heat depofited by the air, is not fufficient to fupport the temperature of the arterial blood, fome degree of cold will be produced in confequence of the change which the blood undergoes in the lungs. As animals are continually abforbing heat from the air, if there were not a quantity of heat carried off, equal to that which is abforbed, there would be an accumulation of it in the animal body. The evaporation from the furface, and the cooling pow. er of the air, are the great caufes which prevent this acccu'nulation. And thefe are alternately in- creafed and dimi'ufhed, in fuch a manner, as to pro- duce an equal effrd. When the cooling power of the air is uiminifhed by the fummer heats, the eva- poration from the furface is increafed ; and when, on the contrary, the cooling power of the air is in- creafed by the winter colds, the ey?.poration from the furface i" proportionably diminifhed. Ihe in- fluence of this caufe in preferviug the equality of I 2 heat ( 68 ) heat in animals, was firft fuggefted to me by my ingenious friend, Mr. Cleghorn. 3 Among different animals, thofe are the hot- teft, which breathe the greateft quantity of air in proportion to their bulk; and in the fame animal, the degree of heat is in fome meafure proportiona- ble to the quantity of air inhaled in a given time. Thefe varieties appear to be the neceffary confe- quence of the general fad, that the heat of the breathing animals is derived from the air. For if animal heat depends upon a change which the air undergoes in the lungs, it is evident, that, all other circumftances being equal, the greater the quantity of air which is changed in a given time, the greater muft be the heat produced. In exercife, by the adion of the mufcles, the ve« nous blood is returned in greater quantities than u- fual, from the extremities, to the right auricle of the heart. By the adion of the heart it is determin- ed to the lungs. The refpiration is accelerated ; the velocity of the circulation is increafed ; and hence, a proportidnable increafe in the quantity of phlogi- fton difcharged, and the quantity of heat abforbed. The cold ltage of fevers is preceded by langour, a fenfe of debility, and a diminution in the action of the heart and arteries. The refpiration is final), the pulfe is weaker than natural—the quantity of blood which paffes thro' the lungs, in a given time, is diminifhed—and hence, lefs phlogifton will be difcharged from the blood, and, confequently, lefs heat will be feparated from the air. In the progrefs of the cold flage, a fpafm is form- ed upon the lurface*. By the conftridion of the veffels on the furface, the blood is determined to the heart. The heart is ftimulated to more frequent and * See Cullen's firft Lines of the Praftice of Phyfick. ( 69 ) and violent contradions. The velocity of the blood through the lungs is increafed-----the refpiration is accelerated; and hence a greater quantity of heat will be abforbed. We may bbferve, that the abforption of heat, and the accelerated velocity of the blood through the lungs, will ad and read upon each other, in fuch a manner, as that the heat will have a conftant pen- dency to increafe. For the accelerated velocity of the blood occafions a greater abforption of heat; and the increafed abforption of heat, by flimulating the heart and arteries to more frequent and powerful contradions, will again accelerate the velocity of the blood, which will ftill farther increafe the abforp- tion. And therefore, the heat will continue to be accumulated, till counteraded by the operation of fome other caufe. From the hidden diminution in the weight of the body, notwithflanding the quan- tity of watery fluids that are taken in, and the ob- ftrudion of the urinary fecretion, it appears, that, in the hot ftage of fevers, there is a very great eva- poration from the furface; we may, therefore, con- clude, that this is one of the means which Nature employs, for moderating the heat, and reftraining the violence of the difeafe. Another caufe which prevents the accumulation of heat, is the cooling power of the external air. We have already obferved, that the quantities of heat loft by a body in a given time, are in proportion to the excefs of its heat, above that of the furrounding medium. If, therefore, the fenfible heat of the body increafe, while the. temperature of the air continues the fame, the quantities of heat carried off by the latter, in a given time, will be proportionably increafed. In putrid fevers, to the accelerated velocity of the blood through the lungs, there is added a putrescent ftate ( 70 ) ftate of the fyftem; in confequence of which, the air inhaled in infpiration, will be more copioufly fupplied with phlogifton, than when the body is in a found and healthy ftate. If, in the latter inftance, the air which is received into the lungs, were completely faturated with phlogiflon, the quantity of heat fepa- rated from it, would always be proportionable to the quantity of air inhaled in a given time. But it ap- pears from experiment, that the air which is expired by a healthy animal, is not completely faturated with phlogifton. It is capable of being farther diminifhed by nitrous air, and not more than the eighth part of it confifts of fixed air. The quantity of heat, there- fore, which is feparated from the air in refpiration, will be partly in proportion to the quantity of air in- fpired, and partly to the quantity of phlogifton dif- charged from the blood, in a given time. In fevers of the putrid kind, as the folid and fluid parts of the fyftem are in a putrefcent ftate, and, con- fequently, retain their phlogifton wifh lefs force, a greater quantity of this principle will be difcharged from the lungs, the air will be more copioufly fup- plied with it in the procefs of refpiration, and will, therefore, impart to the blood a greater proportion of its abfolute heat. To thefe caufes it is probably owing, that the heat of the human body never riles fo high as in putrid fevers. 4. Topical inflammation is accompained with red- nefs, with tumour, and with unufual heat*. From the throbbing of the veffels, and from microfcopi- cal obfervations, it appears, that the velocity of the blood through the part inflamed, is accelerated ; and it is manifeft, that a tendency to putrefadion muft be produced by the violent readion, and by the flag- nation of the ferous matter which is fometimes effuf- ed into the adjoining cellular texture. It has been already * See Cullea's firft Lines of the Practice of Phyfick. ( 7' ) already obferved, that the arterial blood has a ftrong attradion to phlogifton, and that by its union with this principle, in the courfe of the circulation, it is o- bliged to give out that heat which it had received in the lungs. In the ftate of health, the velocity of the blood through the different parts of the fyftem, and the quantities of phlogifton with which it is fup- plied in thofe parts, are adjufted to each other in fuch a manner, that the heat is equally diffufed over the whole. But, if by any irregularity, the balance be deftroyed ; if, by the increafed adion of the veffels, the blood be urged with greater vio- lence than ufual through any particular part, or, in confequence of a greater tendency to putrefadon,* be more copioufly fupplied with phlogifton, it is mani- feft, that a greater quantity of heat will be extricated in that part, in a given time. This heat will ftimu- late the veffels into more frequent,' and forcible con- tradions, by which the velocity of the blood, and the confequent extrication of heat will be ftill far- ther increafed. On this principle we may probably account for the partial heats which are produced by topical inflammations, and for thofe which arife in hedic and nervous difeafes. It will hereafter appear, that the heat is accumu- lated in topical inflammation, by the increafed veloci- ty of the blood through the part inflamed, in the fame manner as it is accumulated upon the fuel, in combuftion, by direding a ftream of frefh air into the fire. Of the principal Fafls relating to the Inflammation of Combuftible Bodies. i. We have proved, that the fenfible heat in combuftion is derived from the air, and depends upon the feparation of abfolute heat from this ele- ment, C 72 ) pent, by the adion of phlogifton. From hence it is evident, that when the air, in which an inflamed body is confined, is faturated with phlogifton, and deprived of the greater part of its abfolute heat, the fource of inflammation will be exhaufted, and the flame will neceffarily be extinguifhed. And this explains the reafon, why a conftant fucceflion of frefh air is neceffary to inflammation, as well as to the fupport of animal life. 2. It is highly probable, from Dr. Prieftley's Experiments, that dephlogiftieated air contains lefs phlogifton, than any other fpecies of air. And this conclufion will, 1 think, be farther confirmed, if we compare his Difcoveries with the Experiments which have been related above. The fubftances from which dephlogiftieated air is obtained, either contain in their natural ftate very little phlogifton, or they are fuch as have the greater part of their phlogifton feparated, by the force of fire, and-by the adion of the nitrous acid. We have feen that phlogifton diminifhes the abfo- lute heat of bodies; that dephlogiftieated air abounds with abfolute heat; that when a certain quantity of phlogifton is added to this fpecies of air, fo as to re- duce it to the ftate of common air, its abfolute heat is proportionably diminifhed ; and that when a ftill greater quantity is added, fo as to convert it into fixed and phlogiflicated air, it is, in & great meafure, deprived of its abfolute heat. From all which it ap- pears, that dephlogiftieated air contains much abfo- lute heat, and little phlogifton. As the fenfible heat which is produced by combuftion, depends upon the feparation of abfolute heat from the air, by the adion of phlogifton, it is manifeft that the lefs phlogifton, and confequently the more abfolute heat any fpecies of air contains, the longer it muft contribute to the fupport of flame, as well as to the prefervation of animal ( 73 ) animal life. Agreeably to this conclufion, we find, from Experiments I. and X. Prop. i. Sed. ii. that dephlogiftieated air contains nearly five times as much abfolute heat as common air. And Dr. Prieft- ley has fhown, that five times as much fenfible heat is produced by the converfion of it into fixed and phlogiflicated air, as by that of common air; for a candle will continue to burn five times as long in the former, as in the latter fpecies of air : Add to this, that it burns with a much more bright and vivid flame ; and as the quantity of phlogifton is increaf- ed, the brightnefs and vivacity of the flame dimi- nifh, till at length the air becomes faturated with this principle, and the flame is extinguifhed. 3. As the fenfible heat, in combuftion, depends upon a change produced in the air, by the phlogi- fton, which is feparated from the inflammable body; it is manifeft, that (all other circumftances being equal) the intenfity of the heat, muft be in propor- tion to the quantity of air which is changed in a given time. And hence the heat may be increafed to a very great degree, if a ftream of frefh air be direded upon the fuel, by bellows or by the blow pipe. We have found, that by the converfion of atmof- pherical into fixed air, a quantity of heat is difenga- ged, which would be fufficient to raife the air fo converted to more than twelve times the heat of red hot iron. And indeed the degree of heat, excited by the inflammation of combuftible bodies, would not be lefs than this, if the fire that is thus extricat- ed, were applied to the fixed air alone, and were to remain in the fame concentrated ftate, in which it is at firft feparated from the atmofpherical air. But as fenfible heat has a conftant tendency to an equal diflufion, it will inftantly flow from the point inflamed, and fpread itfeif over the furrounding bo- K dies. ( 74 ) dies. It will be accumulated upon the fuel, abforb- ed by the vapour, and communicated to the atmof- phere : And from the principles which have been eftablifhed above, it is manifeft, that the fame heat which raifes fixed air 13400 degrees, would raile an equal quantity of atmolpheiial air, only the 5^- part of 13400, or 200 degrees. This explains the rea- fon, why the heat is fo intenfe in the flame of a can- dle, and is fo greatly diminifhed at the fmalleft di- ftance from the flame. 4. Tho' it is highly probable that all bodies have their capacities for containing heat changed in con- fequence of the addition or feparation of phlogifton, yet from the experiments which have been recited above, it is manifeft, that the degree of this change is very different in different bodies. We have feen that the capacity of the calx of iron is to that of iton, as 3.1 to 1 ; that the capacity of minium is to that of lead, as 19.9 to 14.7 ; that the capacity of the calx of antimony is to that of the regulus, as 11.6 to 3.9; and that the capacity of arterial blood is to that of venous, as 1 if to 10. It appears, moreover, that different quantities of phlogifton, are required to faturate different bodies. Some of the metals abound more with this principle than others. The quantity of phlogifton which is required to faturate dephlogiftieated air, is much greater than that which will faturate common air; and a greater quantity of phlogifton is required to faturate common air, than an equal weight of arte- rial blood. From thefe fads it follows, that when phlogifton paffes from one body to another, the changes in the capacities of the bodies for containing heat will be different, and unequal quantities of matter will be changed in a given time. Thus, in refpiration, the phlogifton is feparated from the blood and combin- ( 75 ) ed with the air. The diminution which is produ- ced, by this procefs, in the capacity of the air for containing heat, is greater than the increafe in that of the blood; and as more phlogifton. is required to faturate atmofpherical air, than an equal weight of arterial blood, the quantity of the latter which is changed in a given tnie, will be greater than that of the former. When two contiguous bodies, at the fame mo- ment, have their capacities for containing heat re- fpedively increafed and diminifhed, it the changes be fuch, thac the whole heat feparated from the one is abforbed by the other, no fenfible heat or cold will be produced. I fhall proceed' to determine the cafes in which this will happen, having firft pointed cut fome of the chief circumftances, by which, the fenfible heat of bodies, the capacities for containing heat, and the abfolute heat contained, may be diftinguiihed from each other. The capacity for containing heat, and the abfo- lute heat contained, are diftinguiftied as a force from the fubjed upon which it operates. When we fpeak of the capacity, we mean a power inherent in the heated body ; when we fpeak of the abfolure heat, we mean an unknown principle which is re- tained in the body, by the operation of this powcrj and when we fpeak of the fenfible heat, we confider the unknown 'principle as producing certain erlects upon the fenfes and the thermometer. The capacity for containing heat may continue unchanged, while the abfolute heat is varied without end. If a pound of ice, for example, be fuppofed to retain its folid form, the quantity of its abfolute heat will be altered, by every increafe or diminution of its fenfibie heat : bur as long as its for.n continues the fame, its capacitv for receiving heat will not be K 2 aflcdc4 ( 76 ) affeded by an alteration of temperature, and would remain unchanged, though the body were wholly deprived of its heat. The alterations which are produced in the fenfi- ble heats of different bodies, by given quantities of abfolute heat, are greater or lefs, according as the body, to which the heat is applied, has a lefs or greater capacity for containing heat. Thus it has. been proved, that if a quantity of heat be added to a pound of water, which is fufficient to produce ?n increafe in its temperature as i, the fame quantity of heat being added to a pound of antimony, will produce an increafe as 4. The body, therefore, which has the lefs capacity for containing heat, has its temperature more augmented by the addition of a given quantity of abfolute heat, than that which has the greater. Hence the fenfible heat of a body depends partly upon the quantity of its abfolute heat, and partly upon the nature of the body in which this heat is contained, and confequently the fenfible heat may be varied, either by a change in the nature of the body itfelf, or by a change in the quantity of its abfolute heat. If the variation of fenfible heat arifes from the firft of thefe circumftances, it fol- lows, that, in the fame body, the fenfible heat may vary, though the abfolute heat continues the fame*. The following proportions obtain, with refped to the capacities, the fenfible heats, and the quantities of abfolute heat. The capacities of bodies for receiving heat, are confidered as proportionable to the quantities of ab- folute heat which they contain, when the quantities of matter are equal, and the temperature are the fame. Calling, therefore, the fenfible heat S, the capa- * See the obfervations on fixed and atmofpherical air, venous and arterial blood, page 57. ( 77 ) capacity C, and the abfolute heat A, if the quantities of matter, and the fenfible heats be given, the capa- cities will be as the abfolute heats ; or if S be given, A will be as C. Again, it has been fhown, that, in the fame body, if the form remain unchanged, or, in other words, if the capacity be given, the quantity of abfolute heat will be in proportion to the fenfible heat. That is, if C be given, A will be as S. Since, therefore, if S be given, A will be as C, and if C be given, A will be as S, it follows that if neither be given, A will be as SxC. Therefore, C will be as £• and if A be given, C will be reciprocally as S. Confequently, if the capacities be reciprocally as the fenfible heats, the quantities of abfolute heat will be equal. Thus, if the capacity of the calx of anti- mony be to that of the regulus as 3 to i, and if the fenfible heat of the former be to that of the latter 1 to 3, the calx and regulus will contain equal quanti- ties of abfolute heat *. It appears, therefore, that in heterogeneous bo- dies, if the fenfible heats be different, the capacities may vary, though the abfolute heat be the fame. And it is manifeft from the foregoing experiments, that, in fuch bodies, if the capacities be different, the ab- folute heats may vary, though the fenfible heat be the fame. Thefe obfervations being premifed, the cafes in which no fenfible heat or cold will be produced, by the paffage of phlogifton from one body to another, may be determined in the following manner. PROPO- * The fenfible heat is here fuppofed to be computed from the point of total privation ( 78 ) PROPOSITION I. LET there be two bodies, A and B, which j^ -g have their capacities for nr\ a r r~\ 4fc i containing heat changed L L ;> *5 c K U W k at the fame moment, the H h P p capacity of A being di- minifhed, and that of B increafed ; let the capacity of A before the change, be denoted by C, and after the change, by c ; the capacity of B before the change by k, and after the change by K. Then C—c will be the difference of the capacities of A before and after the change ; and K—k the difference of the capacities of B. It is affirmed, that, if the tem- peratures and the quantities of matter changed in a given time, be equal, the differences ot the capacities will be as the differences of the abfolute heats. For the capacities of bodies for receiving heat, are eftimated (as was obferved above) by the com- parative quantities of abfolute heat which they are found to contain, when the quantities of matter are equal, and the temperatures are the fame. The temperature and the quantities of matter, therefore, in A and B being equal, the capacities will be di- redly as the abfolute heats. If the abfolute heat of A be double that of B, the capacity will be double, If triple, triple, &c. And therefore, call- ing the abfolute heats of A and B before the change, H and p, and after the change h and P, it will be C : c : : H : h. And by converfion C—c: c:: H—h: h. For the fame reafon K—k: k :: P—p : p. But be- caufe the quantities of matter in A and B are equal, and the bodies before and after the change are con- ceived to be brought to the fame temperature, it will be, c: k :: h : p. Since ( 79 ) Since therefore C—c : c : k : K—k H—h : h : p : P—p, by equality C—c : K—k : : 11—h : P—p. That is, the differences of the capacities are as the differences of the abfolute heats, the tempera- tures and the quantities of matter being equal. PROPOSITION II. IF Hie differences of the capacities be equal, the differences of the abfolute heats will be as the quantities of matter*. The fame things re- A i. 2. B maining as above, if the c ^ *L K fS 8) k quantities of matter in A ^ ™ v_/ ™ and B be equal, C—c: H h P P K—k : : H—h : P—p. Let the quantitity of matter in A ^ « be increafed, in any proportion, as /— Ji in Fig. 3, and, after the increafe, let \ J izzi) it be called T. Let the abfolute -n heats be denoted by R and r, and the quantities of matter in A (or B) and T, by q and Q^refpedively. Since the capacities of A and T are equal, the abfolute heats before the change, will be as the quantities of matter. Therefore H : R : : q : Q^ For the fame reafon the abfolute heats, after the change, will be as the quantities of matter. That is, h : r : : q : Q^ Therefore, II : R : : h : r, and H : h : : R : r, and H—h : h : : R—r : r, and H—h: R—r : : h : r. But h : r : : q : CK Therefore H—h : R—r : : q : Q^ But H—h is equal to P—p. There- fore P—p : R—r : : q : CX And hence the differences of • In this and the foflowing proportion, the bodies are fuppofed to be brought to the lame common temperature before and atter the rhumre. ( So ) of the capacities being equal, the differences of the abfolute heats will be as the quantities of mat- ter. PROPOSITION III. I F the differences of the abfolute heats be equal, the differences of the capacities will be reciprocally as the quantities of matter. For, by the firft propofition, the CQ® c quantities of matter being given, the H h differences of the abfolute heats are diredly as the differences of the capacities; and, by the fecond propofition, the differences of the capacities being given, tljie differences of the abfolute heats are as the quantities of matter ; it follows, that neither be- ing given, the differences of the abfolute heats, are as the differences of the capacities, multiplied into the quantities of matter. That i.«, H—h is as C—c X Q. Therefore C—c will be as^; and if H—h be given, C—c will be reciprocally as Q. Confequent- ly if the differences of the abfolute heats be equal, the differences of the capacities will be reciprocally as the quantities of matter. Cor. I. It is, therefore, required, in order that neither heat nor cold fhould be produced, that the differences of the capacities fhould be reciprocally as the quantities of matter changed in a given time. For in that cafe, by the converfe of this propofition, the differences of the abfolute heats will be equal. Cor. II. See the Fig. Prop. I. If, therefore, the diminution in the capacity of A, be to the increafe in that of B, in a greater proportion, than the quantity of matter in B to that in A, the whole of the heat which is feparated from A will not be ab- forbed ( 8. ) forbed by B, a part of it will become redundant, or will be converted into moving and fenfible heat. Cou.. III. The differences of the capacities being reciprocally as the quantities of matter, if the quan- tities of matter changed in a given time be equal, the differences of the capacities will be equal. Cor. IV. See the fig. Prop. I. If the quantities of matter changed be equal, and if the heat of A, after the change, be equal to that of B previous to the change, that is, if h be equal to p, in order that neither heat nor cold fhould be produced, it is re- quired that P (hould be equal to H. For in that cafe II—h = P—p. Cor. V. The fame things being fuppofed, if h be lefs than p, then P muft be greater than H, and P will be equal to H + p—h. For in that cafe H—h will be equal to P—p. Cor.. VI. If h be greater than p, P muft be lefs than H, and P will be equal to II—h—p. For Tub- trading h—p from H, we have H—h+p=P. And, therefore, P—p = H—h. The rule which is expreffed in the firft corollary, applies to the feparation of heat from the air, and the abforption of it by the blood, in the procefs of refpiration. For as the fenfible heat in the lungs, is not greater than in the other parts of the body, it is manifeft, that the whole of the heat which is fe- parated from the air muft be abforbed. And there- fore the changes produced by the paffage of the phlogifton, from the blood to the air, are fuch, that the difference of the capacities of venous and arte- rial blood, is to the difference of the capacities of fixed and atmofpherical air, as the quantity of air changed in a given time, is to that of blood : in which cafe, by the above corollary, no part of the heat will become redundant. The oppofite changes, therefore, which the air and the blood undergo in L the ( S2 ) the lungs, precifely balance each other. For as the quantity of blood, which is altered by refpiration, in a given time, is much greater than that of air, fo tlie change which is produced in the air, during this procefs, is proportionably greater than that which it produced in the blood. The rule which is expreffed in the fecond corrol- lary, applies to the fenfible heat produced in the coure of the circulation, and to that which is pro- duced by the inflammation of combuftible bodies. As we find, for example, that a part of the heat which is difengaged from the blood, in its prog re fs through the fyftem, becomes redundant, we may conclude, that the diminution in the capacity of the blood, is to the increafe in the capacity of thofe parts of the body from which it receives the phlo- gifton, in a greater proportion, than the quantity of matter in the latter to that in the former : in which cafe, the whole of the heat feparated from the blood will not be abforbed; a part of it will be converted into moving and fenfible heat. That this rule is alio applicable to the inflamma- tion of combuftible bodies, appears from the fol- lowing experiments and obfervations. In the burning of oil, the phlogifton is feparated from its former bafis, and combined with the air. The air is converted into fixed and phlogiflicated air—the oil into vapour. By this procefs, the capa- city of the air for containing heat is diminifhed, and that of the oil increafed. And, therefore, from the firft and third Corollaries, it follows, that if, in the inflammation of oil, equ^l quantities of air and oil were changed in a given time, and if the differ- ence of the capacities of oil and the vapour of oil, were equal to the difference of the capacities of fixed and atmofpherical air, the whole heat feparated from the air, would be ablbrbed by the vapour. The ( »3 ) The difference of the capacities of fixed and at- mofpherical air is 66. The capacity of oil is to that of fixed air, nearly as three to one ; and, there- fore, by the firth corollary, it the whole heat fe- parated from the air were abforbed, and if the quan. titics of air and oil changed in a given time, were equal, the capacity of the vapour of oil wou'd be equal to 67 + 3—1. It would be to that of atmof- pherical air, as 69 to 6y. But we have feen, in the above Experiments, that a pint of atmofpherical air communicates one degree of heat to a pi:G of Wc-rer, the difference of temperature being iYiiy ; and that, in the fame circumftances, the quantity of fenfible heat communicated by a pint of the vapour, produ- ced by the inflammation cf oil, is fo fmall, that it cannoi' be meafured by the thermometer. Li the fecoud place, fuppofing that atmofpherical air has a greater capacity for convalning heat, than the vapour of oil, if the quantity of oil changed in a given time, were proportionably greater than t'rzt of air, in this cafe, as appears from the third Pro- pofition, the whole heat feparated from the air, would be abforbed. The comparative quantities of air and oil, which were changed by combuftion, in a given time, were determined in the following manner : A candle, weighing nearly three ounces, and burning with a large wick, was found to lofe a fourth of an ounce in twenty four minutes, or five grains in a minute. Now, if a candle confumes a gallon of air in a minute, and if the one-eighth part of this confifts of fixed air ; it follows, that about eight grains of fixed air, will be' produced by the burning of a candle, in a minute. From which it appears, that the quantity of air changed in a given time, is much greater than that of oil ; and it has been al- ready proved, that the diminution in the capacity of the air for containing heat, is alfo greater than L 2 the ( 84 ) the increafe in that of the oil ; we may, therefore, conclude, that only a fmall part of the heat fepara- ted from the air will be abforbed ; the reft will be converted into fenfible heat. To place this in another light: if, during the in- flammation of o;l, the whole heat feparated from the air, were abforbed by the vapour, it would follow, that the oiiy vapour mixed with the fixed and phlogiflicated air, which are produced by the inflammation of a grain of oil, would contain as much abfolute heat, as an equal quantity of atmof- pherical air, mixed with a grain of oil. Now it is, well known, that when a candle is fuffered to burn out in air, the whole mafs of fixed and phlogiflica- ted air and oily vapour, is contained in lefs fpace, than the atmofpherical air, previous to the inflam- mation. And yet it appears, from Experiment I. and VI. Prop. I. Sed. II that a pint of this com- pound, contains much lefs abfolute heat than a pint of atinof'pherical air. I have made leveral experiments to determine the quantity of air which is phlogiflicated by the calcina- tion of iron ; and have reafon to believe, that it is at leaft equal to the quantity of metal calcined ; from which we may calculate the heat produced by that procefs. The capacity of atmofpherical air is to that of fixed air, as 67 to 1 ; or as 147.4 to 2.2 : The capacity of fixed air is to that of iron, nearly as 2.2 to 1 ; and the capacity of the calx of iron is to that of iron, nearly as 2.5 to 1. Calling, therefore, the capacity of atmofpherical air, 147.4, and that of fixed air, 2.2, it appears from Cor. 6. Prop. III. that if the whole heat fepa- rated from the air, were abforbed by the calx, the capacity of the calx would be equal to 147.4—2.2—1 = 146.2. The heat of the calx would confequently be ( «5 ) be to that of the metal as 146.2 to 1. But it is as 2.5 to 1 ; and hence, the heat which becomes redun- dant during the calcination of iron, is to the original heat of the iron, as 143.7 to 1 > and it is to that of the calx as 143.7 to 2«5> or as 57*4 to l« It has been before fhown, that bodies, when at the common temperature of the atmofphere, contain at leaft 200 degrees of heat. During the inflammation of iron, therefore, a quantity of heat becomes re- dundant, which would be fuflicient to raife the calx 200 degrees, multiplied by 57.4, or 11480 degrees. And hence we may account for the heat which is produced by the percuflion of flint and fteel. A par- ticle of the metal is ftruck off by the force of the flint. The phlogifton is feparated from this particle, and is left at liberty to combine with the air, in con- fequence of which a quantity of fire is difengaged from the latter; and the heat which is produced during this procefs, is fo intenfe, that the particle of the metal, which is ftruck off, is converted into glafs. Upon the whole, there is fufflcient evidence for concluding, in general, that the heat in combuftion, depends upon the feparation of fire from the air, by the adion of phlogifton ; that a part of this fire is abforbed by the body, which fupports the inflam- mation ; and that the reft becomes redundant, or is converted into fenfible heat. It follows, therefore, that the quantity of fire which is feparated from the air, will be in proportion to the quantity of phlogi- fton which is joined to it in a given time ; and the degree of fenfible heat which is produced, will be greater or lefs, according as a lefs or a greater quantity of this fire is abforbed by the body, which di(charges the phlogifton. In the infla-nmation of alcohol and fulphur, a ve- ry great proportion of the fire which is detached from the air, is imbibed by the aqueous and fulphu- reous ( 86 ) rcous vapour; and, therefore, alcohol and fulphur burn with a pale and weak flame. On the other hand, thofe inflammable bodies which produce little vapour, or which produce a vapour that is capable of abforbing but little heat, as pit-coal, oil, wax, phofphorus, burn with a ftrong and vivid flame; for, in thefe cafes, a great part of the fire which is yielded by the air, is converted into fenfible heat. 1 have thus endeavoured to account for the pheno- mena of combuftion and of animal heat, from the general principle, that the capacities of bodies for containing heat, are diminifhed by the addition of phlogifton, and increafed by its feparation. On this principle, a variety of phenomena may be explained, befides thofe which have been already mentioned. When the nitrous acid is mixed with oil of tur- pentine, the phlogifton is feparated from the oil, and combined with the acid ; the latter is forced to give out a portion of its abfolute heat; part of which is abforbed by the bafis of the oil, and the reft be- comes redundant, or is converted into fenfibie heat. If the fenfible heat be increafed to a certain degree, the phlogifton will fuddenly combine with t.,e air, in confequence of which a great quantity of fire will be extricated, and the whole will explode, with a vivid flame, and with intenfe heat. It is probable, that the vapour of the pure nitrous acid contains as much abfolute heat as atmofpheri- cal air ; for the power of the former in maintaining flame, is nearly as great as that of the latter. In the deflagration of nitre, the acid is converted into vapour ; which being at the fame moment combined witti the phlogifton of the coal, the fire is inftantly difengaged, an elaftic fluid is fuddenly expanded, and a loud explofion produced. The ( 87 ) The ingenious Mr. Bewley has given the following explanation of the fpontaneous accenfion of phofpho- rus. He fuppofes, with Dr. Prieftley, that atmof- pherical air contains the nitrous acid, as a conftituent principle ; and obferving that much heat arifes from the fudden combination of phlogifton, with this acid; he concludes that the phlogifton of the phofphorus is capable of decompofing the air; and that by the union of the phlogifton with the aerial acid, a de- gree of heat is produced fufficient to inflame the phofphorus. The experiments which have been recited above, feem to prove, as Mr. Bewley has fuppofed, that the produdion of heaths the neceffary confequence of the combination of phlogifton with air : But thefe experiments appear moreover to fhew, that this heat arifes from the feparation of a quantity of fire, which was contained in the air as a conftitu- ent principle, and which, in the procefs of combu- ftion, is detached from it, by the adion of phlogi- fton. Dr. Prieftley, has proved that the eledric fluid is capable of communicating phlogifton, to atmofphe- rical air, and of converting it into fixed and phlo- » gifticated air. This fad explains the caufe of the heat which is produced by the eiedric fpark. If a great quantity of eledric matter be fuddenly difengaged from a cloud or from the earth, it will extricate a proportionable quantity of fire in its paf- fage through the air j and thus we may account for the fudden rifing of the thermometer in the time of thun.ier and lightning. It is found, by experiment, that the phenomena of an earthquake may be imitated by a mixture of iron filings and brimftone, made into a pafte with water, and buried in the earth. May not the heat which ( 88 ) which is thus produced be explained in the follow- ing manner ? The attradion of the phlogifton to the acid of the fulphur, will be diminifhed both by the attradion of the iron to this acid, and by that of the water. In the degree of heat which is neceffary to the inflam- mation of fulphur, atmofpherical air is capable of feparating the phlogifton from the vitriolic acid. Is it not probable that by the affiftance of the iron and the water, it may be capable of producing this effcd in the common temperature of the atmofphere? If this be the cafe, it follows, that by the adion of the air, which is diffufed through the fubftance of the earth, upon the phlogifton tf the fulphur, and by that of the iron and water upon the acid, the fulphur will be decompofed; the air will unite with the phlo- gifton ; the iron with the acid ; a quantity of fire will be difengaged from the former, and an inflam- mable elaftic fluid from the latter; and hence a com- motion will be excited, accompanied with noife and the eruption of flame, refcmbling the phenomena of an earthquake. May not a fimilar mixture of fulphureous and me- tallic bodies be produced in confequence of the changes which take place in the bowels of the earth ? May [not thefe bodies be brought into contad with the water and the atmofpherical air which are diffu- fed through the earth's fubftance, or lodged in ca- vities beneath its furface ? By the adion of the air upon the phlogifton, and of the water and the ore upon the acid, may not the fulphur be decompofed, as in the mixture of iron filings and brimftone? In which cafe a quantity of fire will be difengaged, and an elaftic vapour produced, the latter of which, by its fudden expanfion, will excite a commotion in the bowels of the earth, and will at length force its way through the fuperincumbent ftrata. ( 89. ) If iviuch combuftible matter be lodged in the regions where the fubterraneous fires have been kindled, and if this matter be mixed with atmofphe- rical air, or with fubftances, which, by the applica- tion of heat, produce a fluid that is capable of main- taining fire, the inflammation may be augmented to a prodigious degree, and the rarified vapours may carry along with them in their alcent, a great quan- tity of ignited materials abounding with phlogifton, by the expofure of which, the phlogifton will be difcharged, and the flame extended through a large trad of air. In this manner we may probably account for vol- canos, thofe awful inftances of combuftion which are exhibted by nature in the foflil kingdom.* It appears, upon the whole, that a variety of im- portant effeds are produced in the univerfe in con- fequence of the mutual oppofition of phlogifton and fire. Vegetables are elaborated by the affiftance of heat and nioifture, from the elements of earth, air, and water, and by the adion of the folar light, the principles of which the vegetable tribe is compofed, are intimately combined with phlogifton, and are obliged to refign a portion of their abfolute heat. In combuftion, the phlogifton is disjoined from its vegetable bafis, and is combined with the air ; and thus thofe artificial fires are maintained which are fo* neceffary in the economy of human affairs. In like manner, by the powers of animal life, the phlogift- on is feparated from the blood and difcharged by refpiration, in confequence of which a quantity of fire is abforbed from the air, and is communicated to the animal kingdom. M The * The fame dettrine feems to afford an eafy folution of the heat which is produced by fermentation ar.d putrefaction. ( 90 ) The air which was tainted by combuftion and ref. piration, is again purified by the growth of vegeta- bles f; and if this effect be produced by the fepara- tion of phlogifton, it follows that vegetation will reitore to the air that heat which had been detached fro 11 it in the proceffes of refpiration and combuf- tion ; and thus the principles of phlogifton and fire, by the medium of atmofpherical air, will be conti- nu:d!y circulating through the animal and vegetable kingdom. It may be proper to obferve, that the dodrine which i:> advanced in the preceding pages, with re- fpe t ro'the caufe pf animal heat and of combuftion, is the refult of the general fad, that the changes which are produced in the temperatures of different bodies, by the application of given quantities of be st, are different; or, that, the quantities of mat- ter being equal, the fame quantity of heat which raifes one body a certain number of degrees, will raife another a greater or a lefs number, according to the nature of the body to which it is applied. This fad appears to have been fufficiently verified by experiment; and, therefore, the confequences which have been deduced from it, muft, 1 apprehend, be confidered as well founded, whatever be the hypo- thefis which we adopt concerning the nature of heat. For this reafon, I have not entered into the en- quiry, which has been fo much agitated among the iGigliih, the French, and the German philofophers, whether heat be a jubilance or a quality. It is true, I have, in fome places, made ufe of expreflions, which feem to favour the former of thefe opinions. But my fole motive for adopting this language, was becaufe it appeared to be more fimple and natural, and inore confpnant to the fads which had been e- itabhfhed by experiment. At the fame time, I am per- f See Dr. Prieftley's Experiments on Air. ( 9' ) perfuaded, it will be found to be a very difficult mat- ter to reconcile many of the phenomena with the fuppofition, that heat is a quality. It is not ea'y to conceive, upon this hypothefis, how heat can be fe- parated from bodies, by the addition of phlogifton, or how the abfolute hear can be augmented by the feparation of this principle; how the quantify of heat in the air can be diminifhed, and that in the blood, increafed, by refpiration, though no fenfible heat or cold be produced. Whereas, if we adopt the opinion, that heat is a diftind fubftance, or an element fui generis, the phenomena will be found to admit of a fimple and obvious interpretation, and to be perfedly agreeable to the analogy of nature. Fire will be confidered as an elementary principle which enters into the compofition of all known bo- dies. In confequence of the addition of phlogifton, a portion of the fire will be detached, in the fame manner as the nitrous acid, is detached, by the vitri- olic, from an earth or alkali, and therefore refpira- tion and combuftion will be truly chymical proceffes, in which, by the exchange of fire and p.hfoginVn, a double decompofition will take place, and two new compounds will be formed; the blood, or the in- flammable body, parting with phlogifton and receiv- ing fire, and the atmofpherical air parting with fire and receiving phlogifton. I may add, in the laft place, that, if fire be con- fidered as an element, which is capable of uniting chymically with bodies, a table may be formed, exhi- biting the refpedive attradions of phlogifton and fire. As phlogifton feparates from bodies, a part of their abfolute heat, it fhould, be placed at the head of the firft column : And as we do not know of any fub- ftances, that attrad this principle with greater force than the earths of the perfed metals, thefe, perhaps, M 2 fhould ( 9^ ) fhould ftand immediatelv under phlogifton. In great degrees of heat, atmofpherical air icparates phlogifton from all inflammable bodies, and in the common temperature of the atmofphere, from nitrous air arid phofphorus. If, therefore, the attradions be arranged as they take p^ace in confequence of the application of heat, under the earths of the perted metals fhould ftand dephlogiftieated and atmofpherical air ; after which fhould be placed, the bates of all the inflammable bodies, difpofing them according to the degrees of heat which are neceffary to their inflammation, when combined with phlogifton ; and at the foot of the column, fhould ftand nitrous air. Fire fhould be placed at the head of the fecond column ; and if the attradions of bodies to this prin- ciple, be proportionable to the quantities of it, which they are found to contain, when the quantities of matter are equal •, under fire fhould ftand dephlo- giftieated and atmofpherical air—ihe vapour of the nitrous acid, and probably of fome other fluids— arterial blood, water, &c. It is manifeft, however, that much time, and a feries of accurate experiments, would be required in order to the complete inveftigation of this fubjed, APPEN- APPENDIX. J. T may not be amifs to give the Reader a brief account of the Experiments referred to in page 10, which were inftituted by Mr. De Luc, with a view to determine the queftion, whether the thermometer be an accurate meafure of heat; or, in other words, whether the expanfions of the fluid contained in the thermometer, be in proportion to the quantities of heat applied ? It was laid down as a principle, by this philofo- pher, that if equal quantities of the fame fluid be mixed together at different temperatures, the heat will be equally divided between them, from which it was concluded, that a thermometer being immerfed in the warmer fubftance, and aifo in the colder, previous to the mixture, if its expanfions were in proportion to the quantities of heat applied, it would point, after the mixture, to the arithmetical mean, or to half the difference of the feoarate heats. Proceeding upon this principle, he found that when a given quantity of water at 32, was mixed with an equal quantity of the fame fluid at 212, the mercurial thermometer, being immerfed in the mix- ture, pointed to 180, or to the arithmetical mean between 32 and 212 : but the fpirit of wine ther- mometer, C 94 ) mometer, in the fame circumftances, did not point to 180. Thefe Experiments were repeated at dif- ferent temperatures with a fimilar refult; from which it was inferred, that alcohol expands irregularly, but that the expanfions of mercury correfpond, pre- cifely, to the quantities of heat applied. FINIS. Leaves vashed and deaoidlfled with magnesium bicarbonate. Resewed. New all-rag end paper signatures* Unbleached linen hinges* Hand sewed headbands* Rebound in ^ Russell's oasis moroooo with hand marbled paper sides and vellum corners. Leather treated with potassium laotate and neat's foot oil and lanolin* December, 1979* Carolyn Horton A Associates 1+30 West 22nd Street New York, N.Y. 10011