Molecule of a Suhstance and its Chemical Properties. 909 



departure from the normal chemical behaviour of the set. 

 The grouping is however, very marked, the change in the 



value of ^ / — as we pass from one group to another being 



usually greater than the deviations from constancy of the 

 values of one group. 



The values of y~/^ for S0 2 and C0 2 are approximately 



equal to one another ; they behave as if both are substitution 

 products of some primary compound. It may be noted that 

 they are formed in a similar way,, viz. by the burning of 

 carbon or sulphur in oxygen. 



A number of expressions involving other quantities than 

 the temperature can be deduced which possess the same 



T 



property as ^ / — . The expressions can be deduced by 



means of the relations 



T = H 2 gyW^r 2 , .... (a) 



x=«"(£) 2 (2vW) 2 , (b) 



L = EM- (2v /^, . . . . (e) 

 m\mj 



P = h*(£) ,/s '(Sv/Wi)*, • • • • 09 



given by the writer, where p, L, X denote the pressure of the 

 saturated vapour, the latent heat, and the surface-tension of 

 a liquid at the temperature T, and H, k", B, M are constants 

 which have the same values for all liquids at corresponding- 

 temperatures, p denotes the density of the liquid and m its 

 molecular weight. 

 Let us write 



F =ih x « 



By means of equations (a) and (1) we obtain 

 or H 3/2 m 1 v 



where v denotes the molecular volume of a molecule. 



(2) 



