﻿18 The Attraction of Unlike Molecules. 



With these values of D at 273 the values of 



(1/Mx + 1/M 2j */{ (MA)*/2 + (MA)*/2} ! D 



can now be calculated as for the gases, with the following 

 results (treating air as N 2 ): — 



3 H 6 O 2 . C 4 H 8 2 . C 5 H 10 O 2 . C 6 H 12 2 - 7 H 14 O a . 



H 2 -23 -24 -25 '26 '26 



Air -22 -23 -24 '25 *25 



C0 2 -27 -27 -28 -28 -29 



O s H 16 2 . C 9 H 18 2 . (0 2 F 5 ) 2 O. CS 2 . C 6 H 6 . 



H 2 -27 -27 -23 "23 -24 



Air *26 -27 '22 -23 -23 



C0 2 -30 -31 -25 -26 -27 



It will be noticed that with hydrogen and air at the lower 

 members of the ester series and (C 2 H 5 ) 2 and CS 2 , the values 

 are near to the *2 which was about the mean value for the 

 gases, but that they increase steadily as the series is ascended ; 

 so that the result for vapours joins on continuously with that 

 for gases, but shows a decided departure from our empirical 

 result for gases that for temperatures near 0° C. the diffusion- 

 coefficients have nearly the same relative values as if the 

 molecules were forceless. But it should be remembered that 

 the results for vapours are all calculated on the assumption 

 that they obey the gaseous laws, and therefore that care should 

 be taken not to give much weight to them till it is ascertained, 

 either theoretically or experimentally, what is the effect on the 

 diffusion-coefficient of such departure from the gaseous laws 

 as vapours show. 



To carry the subject to the most suitable point at which to 

 leave it at present, it seems best to take all the values of 



(l/lt+WVKMA^+fMA)^}^ 



which have been given in this paper and divide them by the 

 corresponding values of 1+^/2 73, using only the theore- 

 tical values of ]C 2 , calculated according to equation (9) . In this 

 way, according to equation (10), we ought for attracting smooth 

 perfectly restitutional spherical molecules to get the constant 

 1/B273* the same for ail pairs of substances; and the amount 

 of departure from constancy will furnish a good measure of 

 the present degree of incompleteness of the kinetic theory of 

 diffusion, the chief cause of incompleteness being, in my 

 opinion, the assumption of perfect restitutionality in each 

 individual collision. 



