2 Mr. W. Sutherland on the Fundamental 



only, although by his experiments he also put upon a satis- 

 factory footing the only general principle that has yet been 

 discovered in organic thermochemistry ; namely, the principle 

 practically enunciated in different forms by Hess, Andrews, 

 and Favre and Silbermann, that in the formation of salts in 

 solution from their elements each atom contributes an amount 

 of heat which is approximately independent of the other atoms 

 with which it is associated. More recently Tommasi (Comptes 

 Rendus) and others have occupied themselves with this law, 

 which indeed has for some little time been installed in text- 

 books as the one generalization of value that the thermal 

 branch of chemistry has yet contributed to the science. Quite 

 recently Dieffenbach (Abst. Journ. Ohem. Soc. 1890, p. 1206) 

 has tried to show that also in entering into the molecule of an 

 organic compound, an atom of an element always produces the 

 same amount of heat ; and there is no doubt that this has 

 been a fair enough hypothesis with which to investigate the 

 accumulating store of experimental material, but it will be 

 made manifest in this paper that this hypothesis must be 

 abandoned in favour of one which provides for a dependence 

 of the atoms on one another in the matter of heats of com- 

 bination. 



The present paper embodies an attempt to unfold the 

 fundamental atomic thermochemical laws in operation both 

 amongst inorganic and organic compounds. In the First 

 Part, after an introductory chapter, the laws regulating the 

 thermochemistry of the haloid compounds of the metals are 

 developed ; and in the Second Part Thomsen's theoretical 

 systemization of carbon thermochemistry will be gone over 

 step by step with a view to eliminating a few principles that 

 seem untenable, and to re-stating his discoveries in terms 

 harmonious with the principles which will be shown to rule 

 the greater part of thermochemistry. 



One of the chief conditions which contributed to Thomsen's 

 success in the handling of the data of the thermochemistry of 

 the carbon compounds, was that he studied the heat of for- 

 mation of the compounds in the gaseous state. The ideal 

 condition in which the data of thermochemistry should be 

 presented is that in which they relate to the heat of formation 

 at constant volume of the gaseous product from gaseous 

 elements ; for these would be the pure heats of formation of 

 the compound molecule from the elementary, unmixed with 

 latent heats or heat spent in external work. In the thermo- 

 chemistry of the carbon compounds the latent heat of vapori- 

 zation of carbon is unknown, so that Thomsen was not able 

 to put his data actually into the ideal condition, although he 



