DIALTTIC SEPAHATIOX OF GASES BY COLLOID SEPTA. 407 



submerged in water, at 22° C, for forty-eight hours. Only a small portion of carbonic 

 acid remained in the residual gas, which, after being washed with potash, consisted of 



Oxygen 25-77 



Nitrogen .... 74-23 



100-00 



2. With the colloid septum properly supported, as by a stucco plate in the diiFusio- 

 meter covered by a film of rubber (p. 400), a considerable separation of mixed gases can 

 be effected. The constituents of atmospheric air appear to be carried through a film of 

 rubber into a vacuum, nearly in the same relative proportion as the same gases penetrate 

 singly (p. 402). The velocities of nitrogen and oxygen passing separately were observed 

 to be as 1 to 2-556, and hence by calculation. 



Oxygen 21x2-556=53-676 . . 40-46 

 Nitrogen 79x1 =79 . . 59-54 



100-00 



Hence air dialyzed by the rubber septum should consist of 40-46 oxygen and 59-54 

 nitrogen in 100 volumes. Now air from the atmosphere was found to enter the vacuum 

 of the 48-inch diflusiometer-tube, through a disk of rubber 22 millims. in diameter, to 

 the amount of 3-48 cub. centims. in twenty-one hours, under the pressure of the atmo- 

 sphere; therm. 23° to 24° C. Of the 3-48 cub. centims. of gas so collected, 2 cub. 

 centims. were absorbed by pyrogallic acid and potash, representing 42-53 per cent, of 

 oxygen in the dialyzed air. Here the gas Avas transferred from the diffusiometer for 

 examination by depressing the diffusiometer in mercury, and using a very narrow tube 

 of rubber as a gas-siphon communicating between the gas in the diffusiometer and a jar 

 inverted in the mercurial trough. The elastic tube is first filled with mercury, and, 

 being of considerable length, a portion of it is di-awn repeatedly through the fingers so 

 as to throw the mercury and aspirated gas into the collecting receiver. The transference 

 of gases in such circumstances may also be effected with much advantage by means of 

 the vacuum-tube invented by Dr. Hermann Sprengel, as will immediately be shown. 



The process of dialytic separation by means of a rubber septum may be varied in 

 three points, — (1) in the condition of the rubber septum, which may be a film of rubber 

 formed from caoutchouc varnish as well as from distended sheet rubber; (2) in the 

 nature of the support given to the septum, which may be a backing of cotton cloth or 

 of silk (common waterproof cloth prepared by means of caoutchouc varnish, in short), 

 as well as a plate of stucco, earthenware, or wood; and (3) in the means had recourse 

 to for sustaining a vacuum, or at least a considerable degree of exhaustion, on one side 

 of the dialytic septum, while atmospheric air, or any other gaseous mixture to be dialyzed, 

 has access to the other side of the same septum. Or the air to be dialyzed may be 

 compressed on one side of the septum, and left of the usual tension on the other side, 

 inequality of tension on the two sides of the septum being all that is required to induce 

 penetration. 



MDCCCLXVI. 3 L 



