410 ME. T. GRAHAM ON THE ABSORPTION AND 



the tube were occupied by coal-gas, or any other foreign gas, instead of being vacuous. 

 As the inner surface of the tube amounted to 0'1034 square metre and the passage of 

 air to 0*8653 cub. centim. per hour, the passage for a square metre would be 8"37 cub. 

 centims. per hour, or 014 cub. centim. per minute. The rate of penetration through 

 the tube-walls appears to be one-fifth of what was found for the rubber cloth. 



3. Slieet rubber, 1 millim. in thickness. 



Although an increased thickness was no doubt attended by slowness of passage, it was 

 of interest to observe whether the proportion of oxygen per cent, might not at the same 

 time be varied. The sheet used was still, however, as thin as the manufacturer could 

 succeed in cutting from a solid cylinder of wrought rubber by the usual method. The 

 rubber was not vulcanized. The sheet of rubber was made into a bag having 0*149 

 square metre (231 square inches) of surface, a double thickness of felted carpet being 

 placed within the folds of rubber. A glass quiU tube, cemented to the bag, com- 

 municated with the interior of the cavity, and was connected at the other end with 

 Sprengel's tube. After the first exhaustion of the gaseous contents of the bag, for 

 which the aid of an exhausting syringe or air-pump is useful, air continued to infiltrate 

 through the sheet rubber, but very slowly. Of the dialyzed air 11*45 cub. centims. 

 were collected in fom* hours. This air contained 41*48 per cent, of oxygen, with a 

 sensible trace of carbonic acid. The penetration for a square metre amounts to 19*2 

 cub. centims. of air per hour, or 0*32 cub. centim. per minute. 



The same bag, left exhausted for eighteen hours, was found afterwards to yield at 

 once 41*6 cub. centims. of air, containing 40*3 per cent, of oxygen, which had accumu- 

 lated in the cavity of the bag ; therm, about 20° C. 



From a larger bag of similar thin sheet rubber, having a surface of 640 square inches, 

 distended by ten or twelve ounces of sawdust, 21*35 cub. centims. of dialyzed air were 

 obtained in one hour; barom. 761 millims., therm. 19°*5 C. This dialyzed air appeared 

 to consist of 



Oxygen 41*80 



Carbonic acid .... 0*94 



Nitrogen 57*26 



100*00 



It does not appear, then, that the increased thickness of the rubber septum tends to 

 increase the proportion of oxygen in the dialyzed air, while this thickness causes the 

 passage to be proportionally slower. The oxygen appears to attain, but never to exceed, 

 at 20° C, the proportion of 41*6 to 58*4 nitrogen. 



The thick rubber brings notably into view the carbonic acid of the ail*. The small 

 proportion of this gas in air is probably increased in all experiments with the rubber 

 septum, however thin. It was observed to rise so high in a small crowded room, as to 

 negative the inflaming action of the oxygen on smouldering wood. But rubber appears 



