THE DYNAMICAL THEORY OF GASES. 73 



of mutual Interference of the molecules of the two gases. This might be 

 deduced from the observed values of p, for mixtures, but a better method is 

 by making experiments 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 k t for air, hydrogen, and carbonic acid, 



Air ............... & 1= 4-81 xlO 10 , 



Hydrogen ....... &, = 1 42'8 X 1 10 , 



Carbonic acid . . . &, = 3 9 x 1 10 . 



The experiments of Graham in 1863, referred to at page 58, on the inter- 

 diffusion of air and carbonic acid, give the coefficient of mutual interference 

 of these gases, 



Air and carbonic acid ..... ,& = 5'2xl0 10 ; 



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

 of the coefficients of interdiffusion given at page 76 are correct, we find 



Air and hydrogen ...... & = 29'8 x 10 1 



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 experiments such as the earlier observations of Mr Graham. 



I have also examined the transpiration-tunes determined by Graham for 

 mixtures of hydrogen and carbonic acid, and hydrogen 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 car- 

 bonic 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 tunes 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 k = l2'5 x 10 10 , 

 For hydrogen and air ............ k= 18'8 x 10 10 ; 



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

 of mixtures of 



VOL. II. 10 



