﻿12 Mr. William Sutherland on the 



yield values of the diffusion-coefficients by the intervention 

 of quite an elaborate theory of the experiment. 



The outcome of the investigation so far, then, is that v. Ober- 

 mayer's experiments (in continual ion of Loschmidt's) on the 

 temperature variation of diffusion establish at least the 

 approximate truth of the law that the parameter 1 A 2 m 1 ?n 2 in 

 the attraction of two unlike molecules of masses wij, and m 2 is 

 equal to the square root of the product of the parameters 

 lA^n^ and 2 &2 m 2 f° r the like molecules. To test the truth 

 of the law in an independent manner, some experiments have 

 been carried out on the surface-tension of mixed liquids and 

 will be described in another paper. 



Meanwhile there is interesting matter to discuss in con- 

 nexion with diffusion. It can be seen how desirable are 

 experiments on the temperature variation of the diffusion- 

 coefficients of many more pairs of gases. This variation 

 could be prophesied for a large number of pairs of gases by 

 calculating 1 C 2 according to equation (9), using therein the 

 values of /3 and iG 1 given in the paper on the Viscosity of 

 Gases and Molecular Force, but the calculations would 

 possess more interest if carried out in connexion with the 

 experiments than at present. However, as the diffusion- 

 coefficients of many more pairs of gases have already been 

 determined experimentally at one temperature, it seems at 

 first sight to be possible to determine the corresponding 

 values of jG 2 from them in the following manner. Let us 

 write our relation (7) in the form 



D = BT » (1/M 1 + 1/M 2 )* 



{(M 1/ 8 1 )V2 + (M J A)*/2}'(1+,(VT)' • • ( ■> 



where B is a constant the same for all pairs, then for the six 

 pairs of gases already studied, as we know all the variables, we 

 can obtain values of B which ought to be all nearly the same. 

 But when the calculation is made, using the lower value of T 

 in each of v. Obermayer's experiments, which is about 284, it 

 is found that B, instead of being constant, is closely propor- 

 tional to 1+jCg/T, as the following values show: — 



C0 2 & N 2 . C0 2 & H 2 . 00 2 &N 2 0. 2 &H 2 . 2 & N a . & CO. 



10 3 B t ... 209 1-53 2-19 1-58 1-73 169 



lO^B/Cl+A/T).. 1-11 1-12 -94 117 1-17 1-16 



This curious result has some interesting bearings. In the 

 first place, it means that the diffusion-coefficients of actual 

 gases at temperatures about 284 absolute are related to one 

 another almost as they would be if the molecules were force- 

 less spheres, and this explains why the investigators of 



