176 cheiyIical theory* 



rissertation on tor of the present theory, was much inclined to the opinion! 



the nature and , ,. t rr , ■« 



€iftcts of heat, "^at light was RiFordcd by * oxi^en gas ; but he appears io 



h%ht, and com- j^j^v^ supposed that the heat had al=o the same origin. A very 

 celebrated chemist of Italy f also has published the same 

 opinion. Sncceedintr chemists, however, have been ltd tp 

 suppose, that the light was afforded by one of the substances 

 ■ necessary for combustion, and heat by the other, and for cer- 

 tain reasons they have attributed the hoat to the oxij^en, and 

 the lij^ht to the infiammnble. These reasons therefore, it be- 

 hoves us to scrutinize and try tlie weight they have in this af- 

 fair. 



Prmo. — Bodies in the aeriform state contain in equal 

 weights at the same temperure much more caloric than, 

 fluids or solids do. This assertion is true in ose sense; a 

 pound of steam at 212° contains much more latent caloric 

 than a pound of water at 212", in the same manner ts a 

 pound of water at 32° does than as much ice at the same tem- 

 perature. But this rule does not hold with substances of 

 different natures^ otherwise a gaseous substance could not be 

 absorbed by a fluid or solid without a great increase of tempe- 

 rature. But if we add a very small quantity of water to a 

 large portion of ammonical gas, the ammonia is immediately 

 absorbed, but the sensible heat is but little increased ; or if we 

 mix muriatic acid gas with ammoniacal gas, a solid substance 

 is immediately formed, with but little hicreased temperature. 

 The same also is observable on the mixing of carbonic acid gas 

 and ammoniacal gas, the heat in these cases can entirely ix? 

 accounted for from the different capacities which these bodies 

 have for caloric. 



Hence I think wp may la}'^ aside the opinion^ that the con- 

 densation of an aereal substance is the cause of the evolution 

 of heat. For it this were the case, a substance receiving gas- 

 eous form would always produce a decrease of tomperalure; 

 but we do not find that the case, when carbonic acid gas is 

 evolved from lime,, or when a large quanlity of gas escapes m 

 "the deflagration of gun-powder or other si!L>u;uces of the 

 same nature. 



* Lavoisier, Fourcroy, j- Professor B'tr.gritolii- 



