26 Mr. W. Sutherland on the Fundamental 



is that they vary in the same direction, that is to say, when 

 CI — Br diminishes F — CI also diminishes. The fluorides do 

 not give us any light at present, but it is evident that they 

 form a very interesting group for thermochemical study. The 

 oxides, sulphides, and selenides have not been considered in 

 this paper, because their melting-points being unknown it is 

 not possible to calculate their latent heats. 



In the next part of this paper it will be shown how the 

 principles ruling amongst inorganic compounds apply to the 

 organic. 



Part II. 



Organic Compounds. 



The method which it is proposed to pursue in this part is 

 simply to follow Thorn sen in the successive steps of his gene- 

 ralizations in the fourth volume of his Thermochemische 

 Untersuchungen, and to retain the greater part of his con- 

 clusions which are valid, while rejecting a few that are 

 invalid, or putting a more valid interpretation upon them 

 than was given to them by their discoverer. I have gathered 

 from abstracts of papers published by Thomsen since the 

 fourth volume of his great work, that he has himself aban- 

 doned some of the unsound conclusions. Armstrong has 

 supplied English chemists with a sketch of Thomsen's theory 

 of the thermochemistry of organic compounds in the Philo- 

 sophical Magazine (5th series, vol. xxiii.), along with some 

 criticism of some of the more extremely heterodox opinions 

 on chemical constitution advanced by Thomsen. This second 

 part of the present paper will form another similar sketch, 

 the repetition being unavoidable in the interests of clearness 

 and the new point of view. 



Thomsen confined his attention to the data, determined by 

 himself for about 120 compounds, apparently because he had 

 taken some trouble to devise a method of determining the 

 heat of combustion of all substances as vapours, and wished 

 to avoid making uncertain corrections for latent heat in the 

 determinations of others who experimented on liquids and 

 solids. From the heat of combustion as vapour at the boiling- 

 point he is able, by approximate values of specific heats, to 

 make the small correction necessary for the heat of combus- 

 tion of the substance as vapour (gas) at 18° C. at the constant 

 pressure of one atmo. These results he gives to the nearest 

 ten calories ; that is, to the nearest hundredth of a kilo- 

 calorie in the heat of combustion of a gramme-molecule. 

 But as different experimenters often differ by some kilo- 



