DoBntte of Heaf, with fefpeSi to denfe and elafllc Fluids. jy 



mutual relation of the principles of which thefe particles are conftitutcd. And this con- 

 fideration inculcates an important diftinftion between two proceflcs, which have beea 

 hithertOi if not altogether confounded, feparated at leaft by a di(lin£lion worfe than none : 

 I mean fublimation and vaporization. The flighted attention will (how the abfurditjr 

 (fuppofing it the fame in both) of calling by different names the aftion of caloric upof 

 bodies as they are in a folid or in a liquid ftate. Nor would fo futile a diftinftion pro- 

 bably ever have occurred, had not a real fpecific difference of aftion in the two cafes been 

 obferved to be generally denoted. In the former, nothing but a minute divifion of the 

 parts (which ftiU retained in other refpeds all their former charaflers) was obfervable : 

 whilft, in the latter, there was not merely a comminution of parts, but a total diverfity of 

 appearance. If we fuppofe the acStion of caloric to be in the former procefs, which com- 

 prehends all the fimpleft bodies, that of merely changing the JlruBure and configuration of 

 the particles, whilft in the latter it exerts itfelf in changing the mutual relation of the con- 

 flituent principles themfelves, fhall we not have at once an explanation of the phyfical nature 

 of this diftindlion, and a fatisfaftory due to fome of the moft important phenomena 

 of nature ? 



Before we advert to the evidence of fa£ls, let us fee how far analogy would carry us in 

 making fuch a change in the conftituent principles of compound bodies as a probable account 

 of the adlion of caloric in their vaporization. As the ordinary procefles of diftillation fo 

 frequently exhibit to us the feparation of the parts of chemical compounds from each other, 

 according to their refpedtive degrees of volatility, and as we can underftand nothing by 

 the different volatility of fubftances but their different, aflinities for caloric, it is obvious 

 that as far as the firft general dictate of analogy is to be trufted, we are decidedly authorized 

 to expeft that all bodies, whofe conftituent parts pofTefs different afHnities for caloric, 

 fliould be liable to the fame decompolition. And fuch an inference can be objefted to 

 only on the ground of fome palpable inconfiftency with the evidence of fa£ts themfelves. 

 The conftruftion hitherto put upon this evidence has been, that bodies which, in common 

 language, preferve their conftitution entire in evaporation, combine with caloric not ac- 

 cording to the difcrete affinities of their feveral parts, but according to their aggregate 

 fpecific affinity for it. How far this afTertion is warranted by the dire£t teftimony of fa£l 

 will be examined prefently. In the mean time it may be remarked that not only the 

 general analogy juft noticed, but all the individual analogies alfo, which are any way con- 

 cerned, unite in contradidllng it. According to this affertion, the conftituent affinity of 

 the parts of water (for inftance) for each other fhould be fo great as entirely to fuperfede 

 the difference of their refpeftive affinities for caloric. But this is not at all confiftcnt 

 with the circumftances which occur in its fynthetical formation ; where foreign aid is 

 always neceffary to eftablifli the fuperiorlty of the former ; and where the caloric con^ant^y 

 given out during the union of the parts gives us ftrong reafon to prefume that its re-com- 

 bination muft indicate their difTolution. Befides, the mere circumftance of expanfion ac- 

 companying the combination of caloric fufficiently indicates its tendency to diffolve iit 



£ a greater 



