of the Theory of Heat. 273 



gen and hydrogen, ov of sulphur and lead, which produces so great 

 a quantity of heat, occasions no greater alteration in the capa- 

 city of water, or of sulphuret of lead, than the combination of oxy- 

 gen with copper, lead, silver, — or of sulphur with carbon, pro- 

 duces in the capacity of the oxides of these metals, or of car- 

 buret of sulphur. 



These facts cannot be easily reconciled with the generally re- 

 ceived ideas respecting the production of heat in chemical phae- 

 iiomena ; for, to do so, it would be necessary to admit the im- 

 probable supposition that heat exists in bodies in two very dif- 

 ferent states, and that the portion which we consider as united to 

 the particles of matter is entirely independent of the specific heats. 

 There is, besides, much vagueness and incoherence in the expla- 

 nations relative to the kind of phsenomena of which we speak. 

 The opinions entertained respecting them differ so widely that 

 they can neither be regularly discussed, nor exposed to complete 

 refutation. — It may perhaps be useful to recall briefly the prin- 

 cipal facts, and the inductions belonging to this important branch 

 of the science. 



Of all the chemical actions considered as sources of heat, none 

 were recognised till lately, except combustion. To search for 

 a plausible theory for this mode of producing heat, before the 

 epoch marked by the memorable discoveries of Lavoisier, would 

 be folly. This illustrious chemist, having more particularly con- 

 sidered the action of oxygen in the state of gas, formed an opi- 

 nion respecting the cause of this phaenomenon, suggested by the 

 observations of Black on latent heat. Hence the idea that the 

 heat liberated during combustion comes from the change of state 

 of the oxygen. The determination which, in concert with La- 

 place, he made, of the cjuantities of heat disengaged by the com- 

 bustion of several substances, appeared to furnish a powerful argu- 

 ment in favour of his conjectures ; for experiment showed that 

 when the same quantity of oxygen was united, successively, with 

 phosphorus, hydrogen, and carbon, it disengaged more heat in 

 the first case than in the second, and more in the second than in 

 the third. This might have been expected from the theory; the 

 result of the first combustion being solid, that of the second li- 

 quid, and that of the third gaseous : but on considering that the 

 two elements which concur to produce water, lose both the 

 gaseous state, and that, notwithstanding, the heat developed is 

 less than what results from the combustion of phosphorus na- 

 turally solid, he was necessarily led to conclude that the latent 

 heat of oxygen must be superior to that of the other elastic fluids. 

 Another difficulty soon after presented itself: nitric acid, in which 

 the oxygen has already lost the gaseous form, and still more nitre, 

 which is in a solid state, produce, when decomposed by combus- 



Vol.5-l.No.258. OcMSiy. S tibles. 



