DIFFUSION OF GASES. 71 



the inference that different gases afford no resistance to each 

 other ; but that one gas spreads or expands into the space 

 occupied by another gas, as it would rush into a vacuum. At 

 least, that the resistance which the particles of one gas offer 

 to those of another is of a very imperfect kind, to be com- 

 pared to the resistance which stones in the channel of a 

 stream oppose to the flow of running water. Such is Dr. 

 Dalton's theory of the miscibility of the gases. (Manchester 

 Memoirs, vol. 5.) 



In entering into this inquiry I found, first, that gases diffuse 

 into the atmosphere and into each other, with different de- 

 grees of ease and rapidity. This was observed by allowing each 

 gas to diffuse from a bottle into the air through a narrow tube, 

 taking care, when the gas was lighter than air, that it was 

 allowed to escape from the lower part of the vessel, and when 

 heavier from the upper part, so that it had, on no occasion, any 

 disposition to flow out, but was constrained to diffuse in op- 

 position to the effect of gravity. The result was, that the 

 same quantity of different gases escapes in times which are 

 exceedingly unequal, but have a relation to the specific gravity 

 of the gas. The light gases diffuse or escape most rapidly; 

 thus, hydrogen escapes five times quicker than carbonic acid, 

 which is twenty-two times heavier than that gas. Secondly, 

 in the case of an intimate mixture of two gases, the most 

 diffusive gas separates from the ether, and leaves the receiver 

 in the greatest proportion. Hence, by availing ourselves of 

 the tendencies of mixed gases to diffuse with different degrees 

 of rapidity, a sort of mechanical separation of gases may be 

 effected. The mixture must be allowed to diffuse for a certain 

 time into a confined gaseous or vaporous atmosphere, of such 

 a kind as may afterwards be condensed or absorbed with 

 facility.* 



But the nature of the process of diffusion is best illustrated 

 when the gases communicate with each other through minute 

 pores or apertures of insensible magnitude. 



A singular observation belonging to this subject was made 

 by Professor Dobereiner of Jena, on the escape of hydrogen 

 gas by a fissure or crack in glass receivers. Having occasion to 

 collect large quantities of that light gas, he had accidentally 



* Quarterly Journal of Science. New Series, Vol. V. 



