320 Intelligence and Miscellaneous Articles. 



ON THE DIFFUSION OF GASES THROUGH CAOUTCHOUC. 

 BY ARONSTEIN AND SIRKS. 



Prof. Byhe needed one day for a physical experiment a long con- 

 tinuous current of pure hydrogen gas. He noticed that, in spite of 

 all precautions, it always contained traces of oxygen, nitrogen, 

 and aqueous vapour. The connexions between the various apparatus 

 for drying and purifying were effected by means of caoutchouc tubes. 

 Hence he imagined the origin of the impurity must be sought in 

 a diffusion of the gases through the caoutchouc. As the statements 

 regarding the permeability of gases through caoutchouc are antiquated 

 and discordant, we investigated the matter, with the following results. 



In one neck of a flask filled with hydrogen a manometer-tube 

 was fitted air-tight ; the other neck, by means of a glass tube fitting 

 air-tight, was placed in connexion with a caoutchouc tube, which 

 was closed by a sealed glass tube. The height of the manometer 

 was so regulated that the pressure for the same volume of gas in the 

 flask could be read off. The diminution of the volume in the flask 

 is then calculated by the formula 



d H(l + a*')' 



where H and t denote the pressure and temperature at the beginning, 

 H' and t' pressure and temperature at the end of the observation, 

 and a the coefficient of cubical expansion of hydrogen. The quantity of 

 hydrogen which has passed out, and of air which has entered, may 

 then be approximately calculated by Graham's law. 



1. An ordinary vulcanized caoutchouc tube, of 3360 square mil- 

 lims'. surface and 1-2 millim. thickness, gave in three days 3=0-0405. 

 This corresponds approximately to h\ per cent, of hydrogen which 

 has passed out, and \\ per cent, of air which has entered. 



2. A brown caoutchouc tube, of the kind called devulcanized, 

 having a surface of 3400 square millims. and a thickness of 1*6 

 millim., gave in twelve days 3=0-049, which corresponds to 6-6 

 per cent, of diffused hydrogen, and 1*7 per cent, infused air. 



3. A tube made of unvulcanized caoutchouc, of about 5000 square 

 millims. surface and 1-3 millim. thickness, gave in twenty-eight 

 days 3=0-168, corresponding to 22*7 percent, of diffused hydrogen, 

 and 5-9 per cent, infused air. 



Caoutchouc may be made impermeable to gases by a coating of 

 asphalte dissolved in tar. The tubes thus coated gave, even after 

 long standing, 3=0. Between caoutchouc and glass there is no 

 diffusion, as was shown in a tube which was firmly bound to glass, 

 and then coated with asphalte and tar, where it was not in con- 

 tact with glass. — Zeitschrift fur Chemie, May 15, 1866. 



Leyden, April 22. 





