Mr. J. C. Maxwell on the Dynamical Theory of Gases. 213 



This expression is reduced to ^ t when j» 2 = 0, and to /j> 2 when 

 p x = 0. For other values of p t and p 2 we require to know the 

 value of k, the coefficient of mutual interference of the molecules 

 of the two gases. This might be deduced from the observed 

 values of fi for mixtures ; but a better method is by making ex- 

 periments on the interdifFusion of the two gases. The experi- 

 ments of Graham on the transpiration of gases, combined with 

 my experiments on the viscosity of air, give as values of h x for 

 air, hydrogen, and carbonic acid : — 



Air k = 4-81 xlO 10 , 



Hydrogen . . . ^ = 142-8 X 10 10 , 

 Carbonic acid . . k ± = 3*9 x 10 10 . 



The experiments of Graham in 1863, referred to at page 199, 

 on the interdiffusion of air and carbonic acid, give the coefficient 

 of mutual interference of these gases, 



Air and carbonic acid . # = 5*2 x 10 10 ; 



and by taking this as the absolute value of k } and assuming that 

 the ratios of the coefficients of interdifFusion given at page 202 

 are correct, we find 



Air and hydrogen . . £ = 29'8xl0 10 . 



These numbers are to be regarded as doubtful, as we have 

 supposed air to be a simple gas in our calculations, and we do 

 not know the value of k between oxygen and nitrogen. It is 

 also doubtful whether our method of calculation applies to expe- 

 riments such as the earlier observations of Mr. Graham. 



I have also examined the transpiration-times determined by 

 Graham for mixtures of hydrogen and carbonic acid, and hy- 

 drogen and air, assuming a value of k roughly, to satisfy the 

 experimental results about the middle of the scale. It will be 

 seen that the calculated numbers for hydrogen and carbonic acid 

 exhibit the peculiarity observed in the experiments, that a small 

 addition of hydrogen increases the transpiration-time of carbonic 

 acid, and that in both series the times of mixtures depend more 

 on the slower than on the quicker gas. 



The assumed values of k in these calculations were — 



For hydrogen and carbonic acid # = 12"5 x 10 10 , 

 For hydrogen and air ... ■ £=18-8 x 10 10 ; 



and the results of observation and calculation are, for the times 

 of transpiration of mixtures of 



