426 Mr. T. Graham on the Molecular Mobility of Gases. 



plain glass cylinder, open at both ends, and about 400 millims. 

 in height (15*75 inches). The upper end was closed by a thick 

 plate of gutta percha cemented on. This plate was itself pene- 

 trated by a wide glass tube, descending about an inch into the 

 jar. The last tube carried the graphite disc, which was 27 mil- 

 lims. (1*04 inch) in diameter, sufficient to close the lower end of 

 the tube upon which it was cemented. The other or upper end 

 of the same tube was fitted with a cork and quill tube, and was 

 put into communication with a large bell jar upon the plate of 

 the air-pump. 



The permeation was slow, owing to the unusual thickness of 

 the graphite plate, occupying three hours to drain away one-half 

 of the original volume of air in the jar. The air remaining 

 behind in the jar was examined in a series of experiments, in 

 which the original volume was reduced to one-half, one-fourth, 

 one- eighth, and one- sixteenth. 



The residual air, reduced to one-half, gave in two experiments 

 21'4 and 21*57 per cent, of oxygen, the air of the atmosphere 

 being by the same analytical process 21 per cent. 



Reduced to one-fourth of its volume, the residual air gave, in 

 two experiments, 21*95 and 22*01 per cent, of oxygen. 



Reduced to one-eighth of its volume, the air gave 22*54 per 

 cent, of oxygen. 



Reduced to one-sixteenth of its volume, the air gave 23*02 per 

 cent, of oxygen. The proportion of oxygen had therefore increased 

 about one-tenth in the last experiment, where the effect is 

 greatest. 



When the numbers are compared, it appears that by a reduc- 

 tion to half its volume the air gains about one-half per cent, of 

 oxygen ; when this last air is reduced to one-half again, another 

 half per cent, of oxygen is gained, and so on — the gain in the 

 proportion of oxygen increasing in an arithmetical ratio, while 

 the volume of air is diminished in a geometrical ratio, or as the 

 powers of the number 2. 



Reduction of 1 volume of air. 



Proportion of 

 oxygen per cent. 



Increase of 

 oxygen. 



To 1 volume 



21 



21-48 



21-98 



22-54 



2302 







0-48 

 0-98 

 1-54 

 202 



To 0*5 volume 



To 0*25 volume 



To 0-125 volume 



To 0*0625 volume 





The densities of oxygen and nitrogen approach too nearly to 

 admit of any considerable separation being effected by this 

 method. The density of oxygen being taken as 1, that of ni- 

 trogen is 0*8785. The square roots of these numbers are 1 and 



