﻿Attraction of Unlike Molecules. 197 



Of the 28 pairs of liquids examined, 24 show a value of the 

 ratio 1 A 2 /( 1 A 12 A 2 )* lying between "9 and 1*1, while of the 

 remaining 4, 2 (ethyl oxide and anilin and ethyl oxide and 

 dimethylanilin) show what appears to be a constant value of 

 the ratio having in one case the value *7 and in the other *8; 

 in the other two cases, namely, those of ethyl oxide and 

 dimethyl anilin and carbon disulphide and methyl iodide, 

 the theoretical equation (6) does not apply as the value of 

 1 A 2 /(iA 12 A 2 )^ is not constant for different values of pi. 

 Some mixtures of ethyl oxide and CS 2 gave a precipitate 

 disappearing only with shaking ; so that perhaps they ought 

 not to rank as genuine mixtures of two liquids. We will 

 not enquire at present more closely into these exceptional 

 cases, nor discuss the great class of exceptions formed by 

 watery solutions and mixtures. In the " Laws of Molecular 

 Force " the method of treating watery solutions was pointed 

 out, and the method will be improved and developed in 

 another paper devoted to the surface-tensions of watery 

 solutions alone. As to watery mixtures it will suffice to 

 instance as the most extreme case of exceptional capillary 

 behaviour the well-known one of mixtures of water and amyl 

 alcohol, water with a surface-tension of 7*4 when mixed with 

 only 2 5 per cent, of amyl alcohol having a surface-tension of 

 3*7 has its surface-tension reduced to 2*8, which is even 

 lower than that of the small amount of added alcohol. It is 

 clear that cases of this sort are complicated with quite another 

 class of phenomena from those we are discussing in con- 

 nexion with normal liquid mixtures, and that we have a right 

 to set them apart for separate study. 



The result X A 2 = ( 1 A 12 A 2 )^, which is the outcome of this 

 investigation on the attraction of unlike molecules, has an 

 important bearing on the interpretation of the data as to the 

 attraction of like molecules contained in the " Laws of Mole- 

 cular Force ;" for evidently the expression Am 2 for the attrac- 

 tion of two like molecules must be regarded as the product of 

 two parameters A^m characteristic of each molecule. The 

 investigation of the attraction of like molecules from this 

 point of view will be taken up in my next paper, " Further 

 Studies on Molecular Force. " 



Melbourne, January 1894. 



