[ 2" 1 



HL A brief 'Examination of the received BoBrines refpetling 

 Heat or Caloric. By Alexander Tilloch. Read 

 before the Afkejian Society, December 1 799. 

 [Ccn.luded from Page 126.] 



X SHALL now endeavour to prove that the pofition which 

 maintains that " heat, when in chemical union in bodies, 

 cannot be made to manif'efl itfelf but by the a&ion of ibme 

 new chemical affinity, does not hold univerfally, and there- 

 fore may fairly be queftioned. 



Gafes, as every one knows, are formed by the folution of 

 certain hafes in caloric. (Whether light be alfo an ingre- 

 dient, or whether light be a modification of heat, or vice 

 verfa, affe&s not the prefent argument,) The bafe or bafes, 

 and the caloric, are chemically united, and therefore the ca- 

 loric, according to the received doctrine, is latent in the gas; 

 it is not cognifable by any external Jign or organ of fenje. I 

 fhall not flop to infift here upon the large increafe of volume 

 acquired by the bafe fo diflblved — an increafe cognifable by 

 our organs of virion, and alfo tangible if the gas be received 

 in a bladder, having already ufed a fimilar argument when 

 fpeakins of the conversion of water into fleam — but proceed 

 to obferve that this chemically combined caloric may be, par- 

 tially at leaft, feparated from its bafe by means merely me- 

 chanical. 



To fuppofe that any body can by mechanical force be re- 

 duced into a fmaller compafs without any portion of its ori- 

 ginal ingredients being thereby driven out of the mafs, would 

 be an abfurditv. When we attempt to comprefs in a metallic 

 veffel, of a known capacity, a quantity of any gas equal in 

 volume to twice that capacity, we, by the mechanical force 

 employed with that view, abfolutely caufe a portion of one of 

 the ingredients in the compofition of the gas to percolate 

 through the materials of which the veffel is made (every fub- 

 flance in nature being pervious to heat). That ingredient, 

 that fuhtfance, is heat. The veffel in this cafe performs the. 

 Office of a liher, fuftering the heat to pafs, but keeping back 

 the other ingredients 5 and the quantity of heat palled off in. 

 L' t % (his 



