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That two heterogeneous bodies (fuch as mercury and water, for inftance), of different temperatures, and which are not known to have any chemical action upon each other, fhould, on their admixture, indicate a temperature, in many cafes, very different from that which would refult from a mixture of two homogeneous bodies, the temperatures of which 'differed in the fame ratio as the former is certainly a fact of no fmall importance towards the acquiring fome knowledge of the nature of that myfterious element-if it be an element-called Fire. Dr. Crawford accordingly, availing himself of this fact, has deduced certain important confequences from it; the juftice of which however is arraigned by the very acute and ingenious Author of the present performance.

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According to Mr. Morgan's expofition of Dr. Crawford's fyftem, fire, or heat, is contained in a great quantity in most bodies, when at the common temperature of the atmosphere; but being in this cafe latent, and producing no effects which render it the object of our fenfes, he diftinguishes it by the appellation of abfolute heat and if this fame principle be fo increafed that it shall exceed the heat of the furrounding medium, and become obvious both to fight and touch, or to the latter feparately, he denominates it fenfible heat.' In other words, if fire, confidered as a component part of bodies, exifts in them only in fuch a quantity, as not to render them warmer than the atmosphere, it is called abfolute heat: but if its quantity be fo large as to produce what is vulgarly called heat, it is then denominated fenfible heat: fo that Dr. Crawford's diftribution of fire into two claffes regards only the quantity, and not any difference in the quality of this principle. According to this idea, equal weights of heterogeneous fubftances may contain unequal quantities of abfolute heat; and the powers which certain bodies poffefs, of collecting and retaining the element of fire in greater quantity than others, Dr. Crawford calls the capacities of bodies for containing heat.

This capacity is greater, for inflance, in atmospherical, and dephlogifticated, that is, pure air, than in fixed and phlogisticated air. Dr. Crawford's experiments lead likewife him to maintain, that the earths or calces of metals poffefs a capacity of containing, and that they actually contain, more heat than the metals themselves and combining thefe two general facts, he deduces from them this confequence; -" that bodies when joined to phlogiften contain lefs abfolute heat than when they are feparated from it," and therefore, "that if phlogifton be added to a body, a quantity of the abfolute heat of that body will be extricated; and if phlogiston be feparated again, an equal quantity of heat will be abforbed." From thefe principles he infers, "that heat and phlogiston appear to be two oppofite principles in nature;"

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and from thence he deduces the whole myftery of com buftion.

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Such is the fubftance of part of Mr. Morgan's explanation of Dr. Crawford's theory of heat, which the latter afterwards applies to account for the production of animal heat. This part of Dr. Crawford's hypothefis, fays the Author, depends fo much on the repugnancy of phlogifton to fire, that if these two principles can be the wn not to be averfe to one another, a theory founded on this mutual averfion, and fupported likewife by fo few experiments, will hardly be thought to deferve much attention.'

The Author then inquires into the principles on which Dr. Crawford has founded his theory; and particularly examines the experiment, which was, we believe, firft made by Fahrenheit, in which a pint of water at 100° F. is mixed with a pint of quickfilver at 50 degrees. In this cafe, we are told that the common temperature of the whole will be nearly 80 degrees; fo that the water will have loft 20 degrees of its heat, and the quickfilver will have gained 30 degrees. Hence it is inferred, that the comparative quantities of abfolute heat in water and quickfilver are as 30 to 20; or, that a pint of water has more heat than a pint of quickfilver in the proportion of 3 to 2; and therefore, the Author adds, the fame quantity of fire, according to Dr. Crawford's reafoning, which will require only two parts of water to contain it, will not be contained in less than three parts of quickfilver.

Mr. Morgan endeavours to fhew, that the conclufions which have been drawn from experiments of this kind, allowing the truth of the results, are not well founded; and illuftrates his objection by alluding to fome cafes refpecting faline folutions. He does not fee that the experiment in queftion proves any thing more than that fome bodies, as Dr. Franklin has obferved, are better conductors of fire than others; or are more or lefs capable of being acted upon by heat, whatever it is. In fhort, he does not perceive that facts of this kind are adapted to prove any particular theory of heat; and on the whole confiders the matter as a fubject which is much more easily controverted than underftood.'

The Author afterwards relates various experiments, which seem to render very queftionable the accuracy of the manner in which Dr. Crawford's experiments were made; and to invalidate the rule on which they are founded. Thus-to give only a few inftances-ufing always equal weights (not bulks) of mercury and water, of different temperatures; in one cafe, the abfolute heats of mercury and water are found to be to each other in the ratio of 1 to 15.9; in a fecond experiment, of 1 to 34.6; in a third, the ratio turns out to be 1 to 32.8. In this experi

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ment, the mercury (at 181°) loft 112 degrees; and the water (at 65°) gained only 3 degrees. In a fourth trial, the abfolute heat of the mercury to that of the water, was in the ratio of 1 to 21.6. In short, the Author produces many experiments, and offers various other observations, to fhew that the conclufions, deduced by Dr. Crawford from his experiments, must be rendered precarious, at least, by the inaccuracies, and the various fources of inaccuracy, which he has pointed out.

Those propofitions particularly, on which Dr. Crawford has founded his theory of Animal heat, are next examined, with the fame attention and precifion; as well as the experiments from which Dr. Crawford inferred the very great quantity of abfolute heat contained in atmospherical and deplogisticated air: while fixed, or impure air, heated, and contained in bladders, is faid to have imparted no more heat to water, than would have been communicated to it by the fame bladder empty, or in a collapfed ftate.

In our Review of Dr. Crawford's performance, we questioned the practicability of deducing any fatisfactory refults from this clafs of his experiments, relative to air, on two accounts. [See M. Review, November 1779, pag. 385, 385.] Thefe were, the extreme Smallness of the scale; and the mistake which we conceived he had made, and which we ftill conceive to be a mistake, in his confounding fixed and phlogisticated air; or, in other words, in confidering atmospherical air, in certain proceffes, fuch as refpiration, combuftion, &c. to be changed into fixed air an opinion, which, though maintained by many refpectable philofophers, has not, to the best of our recollection, been hitherto fupported by any decifive or even plaufible experiment; while there are numerous confiderations that militate against it: the appearance of a small quantity of fixed air, in certain phlogistic and other proceffes, being eafily accounted for, by confidering it as either previously exifting in, and now precipitated from, the atmospherical (or even dephlogifticated) air, in which the experiment was made; or as furnished by fome of the materials employed in the process. With respect to this laft particular the fame portion of charcoal, for inftance, will, for a long time, continue to furnish fixed air in numerous and various proceffes; and even, when at length its phlogiston is all diffipated, and it is reduced to white afhes, the fmall quantity of alcaline falt contained in them, is ftill found to be in a mild ftaté, that is, to contain fixed air. But to return from this seeming digreffion from our immediate subject ;-though it can fcarce be properly called a digreffion: as Dr. Crawford, in accounting for the heat produced in combuftion, founds his reafoning on the fuppofition that fixed air is a combination of common REV. May 1781.

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air and phlogiston; and that, in the procefs of combustion, common air is immediately changed into fixed air.

His prefent Examiner, who likewife controverts this laft pofition (from which Dr. Crawford had inferred that atmosphe rical air, by being fuddenly converted into fixed air, is capable of raifing the latter 13,400 degrees, or to 12 times the heat of red hot iron') relates feveral experiments, made with the affiftance of a particular and commodious apparatus, here described and delineated. From thefe it appears, that no one kind of air feems to have a greater power of heating water than another; nor does one fpecies of air contain more abfolute heat than another. In fhort, according to his experiments, to which we cannot avoid giving full credit, the effects of heated air, pure or impure, mixed with cold water, are nearly imperceptible; or, if perceptible, are fuch as may very eafily be accounted for, from the unavoidable inaccuracies in making the experiment.

Dr. Crawford's third propofition" that the capacities of bodies for containing heat are diminished by the addition of phlogiston, and increafed by the feparation of this principle."-is contested by the Author; firft, as being founded only on a few experiments, and these too, made on one clafs of bodies: they cannot therefore justify a general conclufion applicable to all bodies. To fay that every fubftance in nature has less heat in proportion as its phlogifton is increased, merely because metals may have this property, is to take a vaft deal too much for granted, and to betray a greater fondness for fyftems than appears to be confiftent with true philosophy.'-In the fecond place, admitting even that tin, lead, iron, and antimony, nay that all metallic fubftances have their heat diminished in proportion as their phlogifton is increased; or that they contain lefs heat than their calces; the Author proceeds to fhew, by a few experiments, that this propolition is not true with refpect to fome other bodies; and concludes from thence that Dr. Crawford's fyftem is not founded upon an univerfal law of nature. The objects of the Author's four experiments, refpecting this fubject, are drawn from the vegetable and mineral kingdom. Saw duft, or wood, containing all its phlogifton, is put to the trial with potafhes, or wood deprived of its phlogiston; and pit coal is opposed to its afhes. Both thefe fets of experiments feem to bear their teftimony. against Dr. Crawford's too general propofition. The abfolute heat of crude wood to that of calcined wood was found to be in the ratio of 23.6 to 7.8, or of 3 to 1; and the heat of coal to that of calcined coal, in the ratio of 5 to 3.4.

The Author's laft fection contains many pertinent obfervations, with respect to feveral remarkable facts relating to heat and combustion; and which Dr. Crawford had noticed, as re

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ceiving an easy folution from his fyftem. Mr. Morgan fhews, that the heat which is known to be produced in thefe cafes, and for the production of which Dr. Crawford accounts, by fuppofing it to be occafioned by a decompofition of the air, may be produced likewife in vacuo, or in an exhaufted receiver, in air containing phlogifton. Thus the heat produced by a pafte formed of iron filings, fulphur, and water, takes place even when the materials are expofed to impure, that is nitrous air. Again, the heat and flame produced on the admixture of effential and other oils with fpirit of nitre; the heat occafioned by the attrition of a flint and fteel; and that produced by the electric fpark, have all been obferved to take place in vacuo. In the last mentioned cafe, the Author drew the fparks from a very large conductor, through a vacuum one inch long, and of an inch in diameter. The mercury rose in less than a minute two degrees; nor did he find it rife much, if at all, fafter, when he made the sparks pass through common air, exactly in the same circumftances.

One of Dr. Crawford's obfervations, or rather deductions from fome complicated experiments, which the Author particularly notices, is, that the fame heat which raises common air one degree, will raise fixed air 67 degrees.' This affertion appeared fo extraordinary to the Author, and at the fame time, if true, fo eafy to be verified, that he determined to put it to the teft of a direct experiment: for if heat produced effects fo immenfely greater on fixed, than it does on common air; these effects fhould be vifible in a thermometer fufpended in each.

Two thermometers were accordingly fufpended in two feparate bladders, one of which contained a pint of fixed air, and the other an equal quantity of common air, both at the temperature of 75 degrees. Plunging both the bladders at the fame inftant into a pail of water at 150°; the mercury was feen to rife as faft in the fixed as it did in the common air. Inflammable air was tried in the fame manner; and alfo phlogisticated and deplogisticated airs; in which cafe, the one ought to have heated 300 times falter than the other:' but the refults of all these experiments were much the fame.

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It may be alleged, fays Mr. Morgan, that Dr. Crawford's meaning is only that common air, in a given degree of fenfible heat, contains, in a latent ftate, 67 times as much heat as fixed air of the fame degree of fenfible heat; yet, if by the degree of abfolute heat he meant, what alone it properly fignifies, the different capacities of being heated and cooled, or different fufceptibilities of the action of fire; then does this experiment undeniably prove, that there is no difference in the degree of this abfolute heat in fixed and common air. Were there any fuch difference, the thermometer would rife fafter in the one than in the other; A a 2

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