Si6 



a constant 



Radius of the Sphere of Action of a Molecule. 



and if c 1 varies with the temperature the value of 



is the same for a]l liquids at corresponding states, or the 



diameter of the sphere of action of a molecule is at corre- 

 sponding states the same fraction of the diameter at the abso- 

 lute zero. We have shown * that the law of attraction between 

 two molecules is given by a function of the general form 



where a — pjp c , /3 = t/t c , and z is the distance of separation 

 of the molecules. It follows from this that the factor which 

 expresses the variation of the diameter of the sphere of action 

 with temperature must have the same value for all liquids at 

 corresponding states, which agrees with the above result. 



We have seen that if the function which expresses the 

 variation of the force of attraction between two molecules 

 with their distance of separation is the same for all molecules, 

 the radius of the sphere of action must be of the same 

 magnitude, apart from the effect of temperature, for all kinds 



of molecules. In that case ~—^- should have the same value 



L oPo 

 for all liquids, and T - should have the same value at corre- 



A, 



sponding states since the temperature factor is then the same. 



Now this is approximate! v realized. The values of -y- for a 



number of liquids at corresponding temperatures are given in 

 Table II. It will be seen that they are approximately 



Table II. 



Name of liquid, 



Ether 



Methyl formate 



Benzene 



Carbon tetrachloride 



Chlorobenzene 



Ethyl acetate 



T C 2 



3 ' 



X. 



P- 

 •6907 



75-44 



X 



311-7 



14-19 



i 

 •272 ! 



324-7 



19-80 



•9283 



92-85 



•230 ! 



374-3 



17-87 



7826 



81-73 



•279 



371-0 



1669 



1-4385 



39-87 



■291 



422-0 



17-78 



•9611 



65-88 



•281 



348-3 



17 01 



•8305 



78 61 



260 



constant. The slight deviations from constancy are probably 

 due, as has already been remarked, to the fact that the centres 

 of the atoms of a molecule are not concentrated at a point. 



Cambridge, March 10, 1910. 



* Loc. at, 



