414 Mr. T. Graham on the Absorption and 



gaseous diffusion, which favours the nitrogen or lighter gas, 

 while it is the oxygen which is found to pass through the mate- 

 rial most readily in these experiments. The imbibition of the 

 liquefied gas by the substance of the rubber, with the subsequent 

 evaporation of this liquid into the vacuum on the other side, is 

 all the explanation required. 



2. Vulcanized india-rubber tubing. 



A stout caoutchouc tube with an external diameter of 13 mil- 

 lims. (half an inch), an internal diameter of 9 miliims., thickness 

 of 2 millims., and length of 3*658 metres (4 yards) was exhausted, 

 one end being closed and the other end connected with the 

 Sprengel pump. The gas collected in thirteen hours amounted 

 to 11-25 cub. centims. ; therm. 20° to 23° C. This gas con- 

 tained 37*8 per cent, of oxygen. The gaseous penetration is not 

 great in so thick a tube, and there is reason to fear the influence 

 of gaseous diffusion to a small extent. The admission of air 

 would be equally sensible if 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 : 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 0*14 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. Sheet 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 manu- 

 facturer 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 quill 

 tube, cemented to the bag, communicated with the interior of 

 the cavity, and was connected at the other end with SprengeFs 

 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 col- 

 lected in four 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. 



