ME. CLEEK. MAXWELL ON THE DYNAMICAL THEOEY OE GASES. 
75 
Time. 
Pi. 
P 
0 
0 
T 
•01193 
2 T 
•02305 
3 T 
•03376 
4T 
■04366 
5 T 
•05267 
6T 
•06072 
8T 
•07321 
10 T 
•08227 
12 T 
•08845 
co 
•10000 
Mr. Graham’s experiments on carbonic acid and air, when compared with this Table, give 
T=500 seconds nearly for a tube 0'57 metre long. Now 
whence 
tw log. 10 « 2 
T’ 
D=-0235 
( 91 ). 
for carbonic acid and air, in inch-grain-second measure. 
Definition of the Coefficient of Diffusion. 
B is the volume of gas reduced to unit of pressure which passes in unit of time 
through unit of area when the total pressure is uniform and equal to p, and the pressure 
of either gas increases or diminishes by unity in unit of distance. D may be called the 
coefficient of diffusion. It varies directly as the square of the absolute temperature, and 
inversely as the total pressure p. 
The dimensions of B are evidently L 2 T -1 , where L and T are the standards of length 
and time. 
In considering this experiment of the interdiffusion of carbonic acid and air, we have 
assumed that air is a simple gas. Now it is well known that the constituents of air can 
be separated by mechanical means, such as passing them through a porous diaphragm, 
as in Mr. Graham’s experiments on Atmolysis. The discussion of the interdiffusion of 
three or more gases leads to a much more complicated equation than that which we have 
found for two gases, and it is not easy to deduce the coefficients of interdiffusion of the 
separate gases. It is therefore to be desired that experiments should be made on the 
interdiffusion of every pair of the more important pure gases which do not act chemically 
on each other, the temperature and pressure of the mixture being noted at the time of 
experiment. 
Mr. Graham has also published in Brande’s Journal for 1829, pt. 2, p. 74, the results 
