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



The dimensions of D 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 car- 

 bonic acid and air, we have assumed that air is a simple gas. 

 Now it is well known that the constituents of air can be sepa- 

 rated by mechaDical means, such as passing them through a 

 porous diaphragm, as in Mr. Graham's experiments on Atmo- 

 lysis. 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 expe- 

 riment. 



Mr. Graham has also published in Branded Journal for 1829, 

 pt. 2, p. 74, the results of experiments on the diffusion of va- 

 rious gases out of a vessel through a tube into air. The co- 

 efficients of diffusion deduced from these experiments are — 



Air and hydrogen . . 



•026216 



Air and marsh-gas . 



•01024 



Air and ammonia . . 



•00962 



Air and olefiant gas . . 



•00771 



Air and carbonic acid 



•00682 



Air and sulphurous acid 



•00582 



Air and chlorine . . 



•00486 



The value for carbonic acid is only one third of that de- 

 duced from the experiment with the vertical column. The 

 inequality of composition of the mixed gas in different parts 

 of the vessel, however, is neglected ; and the diameter of the 

 tube at the middle part, where it was bent, was probably less 

 than that given. 



Those experiments on diffusion which lasted ten hours, all 

 give smaller values of D than those whichlasted four hours ; and 

 this would also result from the mixture of the gases in the vessel 

 being imperfect. 



Interdiffusion through a small hole. 



When two vessels containing different gases are connected by 

 a small hole, the mixture of gases in each vessel will be nearly 

 uniform except near the hole ; and the inequality of the pres- 

 sure of each gas will extend to a distance from the hole depend- 



