28 Mr. W. Sutherland on the Fundamental 



such as OH in KOH, then K is not supposed to be in the 

 same intimate relations with H as it is with 0, so that in the 

 last equation /(RT) would not be expected to be comparable 

 to /(RS) or /(ST) ; and it may be stated that the most 

 important and broadest generalization underlying Thomsen's 

 results is, that the mutual effect of atoms which are not 

 directly united with one another according to the ordinary 

 scheme of formulae, may be neglected with at least a close 

 first approximation to the truth. The mutual effect of un- 

 connected atoms in the organic molecule must therefore in 

 most cases belong to the region of second approximations, 

 and though of the highest interest need hardly be looked for 

 systematically until the accuracy of experimenting is carried 

 still higher ; but a few striking cases will force themselves 

 on our notice even in the present inquiry. There is no 

 occasion to prove by illustrative examples the approximate 

 thermochemical independence of unconnected atoms in the 

 molecule, because, as Thomsen's whole system depends on it, 

 the whole of the rest of this paper will be illustrative of it. 

 Thomsen's method of expressing his results involve the prin- 

 ciple, for he assigns a thermal value to each bond in the 

 graphical formula of a molecule and determines it for several. 

 Thus, for instance, the heat of formation of C 2 H 5 OH from 

 atoms of C, 0, and H is regarded as the sum of a thermal 

 value for the bond joining the two C atoms to one another, 

 for the five bonds joining H to C, for the one joining to C, 

 and for one joining to H ; and there is assumed to be no 

 thermal contribution due to any relations of the atom to 

 the five atoms of alkyl hydrogen or of the hydroxyl hydrogen 

 to the carbon : that is to say, it is assumed that all mutual 

 influences except those due to direct connexion can be 

 neglected. 



There are some instances, as in the ammonium compounds, 

 where the mutual influences of unconnected atoms are of the 

 highest importance ; for the four atoms of H in NH 4 C1 seem 

 to affect profoundly the relation of the N atom to the CI, so 

 that it is quite different from the relation in NC1 3 . But 

 these exceptional cases will not be studied in the present 

 paper, unless when unavoidable. 



We can now proceed to take the subject matter of 

 Thomseir's conclusions section by section. 



1. The effect of CH 2 in the Heat of Combustion of Homo- 

 logous Series. — Each addition of CH 2 in a series increases the 

 heat of combustion by an average amount of 157*9 kcal.; 

 only 5 out of 44 values are more than 1 per cent, different 

 from this average. Accordingly, as a first approximation it 



