268 PHENOMENA DEPENDENT ON MOLECULAR PATHS 100 



which are essentially different values [being in the ratio 

 (tQj/OJ 8 or m 2 /m l , where m denotes the molecular weight]. 



But in the conditions that have chiefly been employed in 

 the experiments we can take for the but slightly variable 

 coefficient the value 



-Afci 



which we find on putting A^ = N 2 . 



1O1. Dependence on Pressure and Temperature 



To test the formula we can also raise the question 

 whether the formula correctly gives the law of dependence 

 of the coefficient of diffusion on both pressure and tem- 

 perature. 



Since both of the mixing gases have the same temperature, 



where m l and m 2 denote the molecular weights of the two 

 gases. If then we denote by m and n the values of the 

 molecular weight and molecular speed for any normal gas 

 which has the same temperature, we have 



By means of this relation the formula for the total pressure 



p = iTrt^rv + # 2 m 2 n 2 2 ) 



takes the simple form 



p = 



wherein N = N l + N 2 signifies, as before, the total number of 

 all the gaseous molecules of both kinds in unit volume. By 

 this formula we may replace N in the formula for D by the 

 pressure p, and we then obtain for the coefficient of diffusion 



D = ^( 

 where 



i + *( + ^2^1 



If we put s^ = = s 2 , these general formulae would turn 



