SS8 On the Heat disengaged during Combination. 



1. 2. 3. 



2243 2275 2347 



We obtain, therefore, for the heat evolved during the com- 

 bination of — 



One gramme oxygen v.'ith protoxide of copper 2288 

 One gramme protoxide of copper with oxygen 256 

 One litre oxygen with protoxide of copper . 3288 



The last four sets of experiments are favourable to the view 

 proposed, I believe, by Dulong, that the quantities of heat 

 produced by the combination of a metal and of its oxide with 

 oxygen are the same for equal quantities of oxygen absorbed. 

 Tims in the case of tin and its protoxide, we have for one 

 gramme of combining oxygen the numbers — 



4.230 

 4.34.9; 



and for copper and its protoxide — 



2394. 

 2288. 



The experiments of Dulong on tin and its protoxide agree 

 with this conclusion. I may remark, however, tliat the results 

 now obtained with the protoxide of copper can only be con- 

 sidered to be approximations ; and that further researches will 

 be necessary to discover whether the above differences will 

 disappear when the true numbers are exactly ascertained, or 

 be increased. The principle will in any case only apply to 

 metals, such as tin and copper, which are capable of forming 

 oxides inferior to those produced by their combustion in 

 oxygen gas. 



Among the gaseous combinations, the heat evolved by the 

 combustion of equal volumes of hydrogen and carbonic oxide 

 is nearly the same, viz. 3036 for one litre of the former, and 

 3057 for the same volume of the latter; but this agreement is 

 more apparent than real, and would entirely disappear if the 

 experiments were made under strictly identical circumstances, 

 that is, in such a way as to obtain the resulting compounds in 

 both cases in the aeriform state. In fact, if we correct the 

 number expressing the heat due to tlie combustion of hydrogen 

 for the latent heat of the vapour of water, it will become re- 

 duced to 254.0, a number which is far from identical with 3057. 



It has been inferred from the experiments of Dulong, that 

 the heat evolved in the combustion of a compound gas is the 

 same as that evolved in the combustion of its constituents. 

 This principle would lead to the very improbable conclusion, 

 that the separation of the elements of the compound gas is not 



