182 Abstract of recent Researches on the quantity of 



bonic oxide, was, to that evolved in burning carbonic oxide, 



as three to two. As, according to his view, 



A vol. of carbon burning to carbonic acid evolves heat 7858 

 A vol. of carbonic oxide burning evolves heat . . .3130 



.*. A vol. of carbon forming a vol. of carbonic oxide evolves 4728 



From this he deduced the curious result, that it would pro- 

 duce more heat in practice (as in smelting-works) to employ 

 all oxygen to form carbonic oxide, than to produce carbonic 

 acid in the proportion of six to five; and hence, that in 

 changing carbonic acid into carbonic oxide, heat should be 

 evolved. These views have, however, been shown to be erro- 

 neous by M. Ebelmen, who proved, by a comparison of De- 

 spretz's - results with those of Dulong, that Dulong considered 

 carbonic oxide to contain half its volume of gaseous carbon, 

 and, consequently, that as 



A vol. of carbon, burning to carbonic acid, evolves 7858 heat, 

 Two vols, of carbonic oxide, burning, evolves . . 6260 



One vol. of carbon, in forming carbonic oxide,~l 1 - q ~ 

 evolves only J 



and hence the quantity thus employed is, to the total quantity, 

 as one to four. 



M. Hess has very ingeniously endeavoured to apply his se- 

 cond law to the determination of several important questions. 

 Thus, to explain the great combustibility of gunpowder, he 

 considers that in forming nitric acid, each atom of oxygen has 

 evolved a certain quantity of its heat, and more in the order 

 of its combination. Thus, if the total quantity of heat be- 

 longing to an atom of oxygen be represented by 16, then the 

 first atom which unites with the nitrogen may be supposed to 

 lose all ; the second 8, the third 4, the fourth 2, and the fifth 1 . 

 There is thus expelled in forming nitric acid, 16 + 8 + 4 + 2 

 + 1 = 31 units of heat; but the total quantity belonging to 

 the oxygen being 16 x 5 = 80, there remain 49 units of heat 

 available for the carbon and sulphur. A very important con- 

 sequence from these considerations, deduced by M. Hess, is, 

 that the heat evolved in the combustion of a compound body 

 is, in all cases, less than the heat evolved in the combustion of 

 its constituents ; because some heat has been already eliminated 

 in the combination of these constituents with each other. This 

 principle M. Hess considers to derive great support from expe- 

 riments made by Dr. Ure on the combustion of certain kinds 

 of fuel and fatty matters, of which there is a notice in the Athe- 

 naeum, 1839, No. 620; but it must be remarked, that the re- 



