the Sphere of Action of a Molecule. 845 



by a constant which depends on the nature of the molecule. 

 This, however, is probably true for atoms only, and the slight 



deviations of the values of ~ from constancy in the case of 



l 



molecules are due to the fact that the centres of the atoms 

 of a molecule do not lie on a point. The change in the law of 

 force introduced in this way should, however, be small. 



The formula for the diameter of: the sphere of action can 

 be transformed into a form which brings out some further 

 properties of this quantity. It can be shown that the internal 

 latent heats of liquids at corresponding states are each the 

 same fraction of the corresponding latent heat at the absolute 

 zero. The writer * has shown that the latent heat L is con- 

 nected with other quantities by the equation 



where p is the density and B a constant which is the same 

 for all liquids at corresponding states, and Sv»i is the sum 

 of the square roots of the atomic weights of the atoms in a 

 molecule. At the absolute zero we have 



L =B ^(V™) 8 =B ^(2 V ^) 3 , 



since we may write p = ap c where a is a constant. We may 

 also write p = ap c where a is the same at corresponding states, 

 and we have 



which by the help of the above equation becomes 



or L 1 = L i) t; where 77 is the same for all liquids at corresponding 

 states. It is also shown in the paper cited that the surface 

 tension at corresponding temperatures is the same fraction of 

 the surface tension at the absolute zero, or \ = /jl\ , where /x 

 is the same for all liquids at corresponding states. We 

 have then 



. dX . \ da 



dL L p c d(r)a)' 

 3nt of the temperati 

 Phil. Mag. p. 507, Oct. 1909, and he. cit. 



Thus if Ci is independent of the temperature, , ( ' , must be 



