DIALYTIC SEPARATION OF GASES BY COLLOID SEPTA. 405 



appears to be modified. Soft rubber, first charged with carbonic acid at 20°, and then 

 made rigid by cold, appeared to lose its carbonic acid, when afterwards freely exposed 

 to air, less rapidly than the same rubber equally charged but exposed from the first in 

 its soft condition. The quantity of carbonic acid retained in the former case was 10'76 

 per cent., and in the latter 7*08 per cent, of the volume of the rubber, after a similar 

 exposure of forty-eight hours. This point, although not sufiiciently examined, is alluded 

 to here on account of the analogy which appears to hold between rubber and the mal- 

 leable metals in a power to absorb a gas when they are softened by heat, and to retain 

 the same gas with great tenacity when they are afterwards made rigid by cold. 



The condensation of oxygen gas by masses of solid rubber punched out of a block 

 was made the subject of observation, by placing 50 grms. of that substance within a 

 jar of oxygen standing over mercury during a period of several days. From the rubber 

 afterwards there was extracted, by the action of a vacuum continued for twenty-one 

 hours, 6-21 cub. centims. of gas ; of which 3*67 cub. centims. were oxygen, 0'14 carbonic 

 acid, and the remainder chiefly nitrogen. Taking the bulk of the rubber at 53'8 cub. 

 centims., the oxygen absorbed amounts to 6 •82 per cent, of the volume of the rubber. 

 Oxygen then may be regarded as fully twice as soluble in rubber as the same gas is in 

 water at the ordinary temperature. No experiment was made at a higher temperature ; 

 but as the penetrativeness of rubber is much increased by heat, the presumption is that 

 the solubility of gases in rubber is increased in the same degree. 



More than one attempt was made to identify the presence of free hydrogen in the 

 substance of rubber after being kept in that gas for some time, but with a negative 

 result. The absorbed hydrogen may be too easily dissipated, owing to its extreme 

 volatility. 



Lialytic separation of Oxygen from Atmospheric Air, (1) by means of other gases, 



(2) by means of a vacuum. 



1. A balloon of rubber filled with hydrogen and exposed to the atmosphere, gradually 

 loses the former gas, which is finally replaced by a considerably smaller volume of air, 

 presenting a deceptive resemblance to the diflfusion of hydrogen gas into air. When 

 the progress of the entrance of air was observed at difiierent stages of the exchange, it 

 appeared that after three hours, when the balloon had fallen from 150 to 128 millims. 

 in diameter, the composition of its contents was — 



Oxygen . . 8-98 41-6 



Nitrogen . . 12-60 58-4 



Hydrogen . . 78-42 



100-00 100-0 



Setting aside therefore the hydrogen still remaining, the balloon now contained a 

 portion of a mixture of oxygen and nitrogen in the proportion of 41-6 volumes of the 

 former to 58-4 volumes of the latter. This was the largest proportion of oxygen to the 



