﻿16 



Mr. William Sutherland on tlie 



have been calculated as given along with the diffusion-coeffi- 

 cients in the following table : — 



H 2 and 



o 2 



N, 



CO. 



CH 4 . 



C0 2 . 



N 2 0. 



C 2 H 4 . 



C 2 H 6 . S0 2 . 



D 273 ... 



•667 



•645 



•647 



•625 



•532 



•532 



•486 



•458 -484 





•195 



•191 



•199 



•193 



•203 



•207 



•194 



•208 -209 



C0 2 and 



o 2 



N, 



N 2 0. 



CO. 



o 2 



and N 2 . 



CO. 



CO and C 2 H 4 . 



±> 273 . . . 



•136 



•135 



•193 



•143 





•178 



•187 



•122 





•205 



•201 



•248 



•199 





•193 



•190 



•237 



The values of 



(l/M 1 + l/M 2 )=/{(M I ,fi 1 )*/2 + (M 2 /3 2 ) i /2} 2 D 



are nearly constant, though showing on the whole a tendency 

 to increase with the number of atoms in the diffusing mole- 

 cules, as we already noted in connexion with 10 3 B/(l + iC 2 /T) 

 for the original six pairs of gases. 



The last table can be greatly extended, thanks to the 

 experiments carried out by Winkelmann for determining 

 diffusion-coefficients according to Stefan's evaporation method 

 founded on his equation marked (5) in the present paper. 

 He has determined the rates of evaporation of a number of 

 esters from C 3 H 6 2 to C 9 H 18 2 , and ethyl oxide, carbon di- 

 sulphide, and benzene in air, hydrogen, and carbon dioxide 

 at different temperatures, and has calculated the corresponding 

 coefficients of diffusion. 



In order to obtain the values of D 273 it is necessary to 

 obtain approximate values of ]C 2 for use in the equation 



D 273 _/273y 1 + iC/T 



"It/ 1+A/273' 



D 



These can be calculated from equation (9) if we know -$ x 

 and M/3 for the esters. The values of x Qj X can be obtained in 

 the following manner : — In the paper on the Viscosity of 

 Gases and Molecular Force it is shown that for compounds 



M^ 1 C 1 10- 2 =21M 2 //2, 



where I is the virial constant of molecular attraction in the 

 characteristic equation of the substance ; values of M 2 / for a 

 large number of bodies being given in the Laws of Molecular 

 Force (Phil. Mag., March 1893) along with methods of cal- 

 culating them for any body. As regards M/3 for the esters, 

 I have found by determining /3 that for C n H 2;i 2? 



M£=29 + 17-5(n-l) 



approximately : thus all the data are to hand for calculating 

 C 2 for each of Winkelmann's diffusing pairs. 



