618 [June 18, 



distinguish it by a peculiar name. The amount of the separation is 

 in proportion to the pressure, and attains its maximum when the 

 gases pass into a nearly perfect vacuum. A variety of experiments 

 were made on this subject, of which perhaps the most interesting 

 were those upon the concentration of the oxygen in atmospheric air. 

 When a portion of air confined in a jar is allowed to penetrate into a 

 vacuum through graphite or unglazed earthenware, the nitrogen 

 should pass more rapidly than the oxygen in the proportion of 1 -0668 

 to 1, and the proportion of oxygen be proportionally increased in 

 the air left behind in the jar. The increase in the oxygen actually 

 observed when the air in the jar was reduced from 1 volume 



To 0-5 volume, was 0'48 per cent. 

 0-25 0-98 



0-125 1-54 

 0-0625 2-02 



Or, the oxygen increased from 21 to 23'02 per cent, in the last 

 sixteenth part of air left behind in the jar. 



The most remarkable effects of separation are produced by means 

 of the tube atmotyser. This is simply a narrow tube of unglazed 

 earthenware, such as a tobacco-pipe stem two feet in length, which 

 is placed within a shorter tube of glass and secured in its position by 

 corks, so as to appear like a Liebig's condenser. The glass tube is 

 placed in communication with an air-pump, and the annular space be- 

 tween the two tubes is maintained as nearly vacuous as possible. Air 

 or any other mixed gas is then allowed to flow in a stream along the 

 clay tube, and collected as it issues. The gas so atmolysed is of 

 course reduced in volume, much gas penetrating through the pores of 

 the clay tube into the air-pump vacuum ; and the slower the gas is 

 collected the greater the proportional loss. In the gas collected, the 

 denser constituent of the mixture is thus concentrated in an arithme- 

 tical ratio, while the volume of the gas is reduced in a geometrical 

 ratio. In one experiment the proportion of oxygen in the air after 

 traversing the atmolyser was increased to 24*5 per cent., or 16' 7 

 upon 100 oxygen originally present in the air. With gases differing 

 so much in density and diffusibility as oxygen and hydrogen, the sepa- 

 ration is of course much more considerable. The explosive mixture of 

 two volumes of hydrogen and one volume of oxygen, gave oxygen con- 



