NEW LAW IN THERMOCHEMISTRY 1 7 



pound, and will be studied with other bodies of like consti- 

 tution. Carbonyl sulphide contains oxygen, and is therefore 

 incompletely dissociated when burned. Carbon disulphide, 

 like the dioxide, belongs in a different class, and must be 

 considered separately. According to Thomsen, its heat of 

 combustion is 265 130 calories, all substances being gaseous. 

 Hence, if / represents the absolute heat of formation of SOj, 

 its equation of combustion is 



.v+ 2/ — 32- — r= 265130, 



and therefore r= 104770 calories approximately, or between 

 seven and eight henotherms. A small change in the value of the 

 henotherm would bring the result near the higher figure, which 

 is probably the one to choose. But new measurements are 

 needed to settle this question. 



There still remain to be examined, in addition to the aro- 

 matic compounds and the carbonyl derivatives, something like 

 fifty other substances which contain, in addition to carbon and 

 hydrogen, more or less oxygen within their molecules. They 

 are, therefore, upon burning, incompletely dissociated ; for the 

 oxygen atoms must remain combined with one or another of the 

 elements associated with them. Furthermore, fewer oxygen 

 molecules are broken up during combustion, and this fact affects 

 the number c of the general formula. The latter, however, still 

 applies, and the same constant appears as its quotient. In all 

 cases c represents the number of oxygen molecules which are 

 decomposed ; but among the compounds hitherto studied it also 

 stands for all the oxygen needed to satisfy the carbon, the 

 hydrogen or the sulphur of the substance burned. 



In the large group of bodies now to be considered, oxygen 

 may exercise any one of three distinct functions. It may link 

 carbon with carbon, as in the structure = C — O — C = ; it may 

 stand between carbon and hydrogen, in the form = C — O — H ; 

 or it may be wholl}^ united with carbon in the group = C = O. 

 In the first of these modes of combination the two unions seem 

 to be normal, giving thermal values which correspond exactly 

 with the hydrocarbons and their dissociable derivatives. To 

 the ethers, then, the normal formula 



