280 Permeability of Films to Hydrogen and Helium. 



XII. Diffusion of Hydrogen through Wet and Dry 



Cotton Fabrics. 



Some experiments were made on the transfusion of 

 hydrogen through a closely woven cotton fabric when wet 

 and also when dry. When this fabric was dry the gas 

 diffused through it so rapidly that it whs impossible to obtain 

 a measure of the rate of transfusion with the katharometer. 

 On the other hand, when the fabric was thoroughly wetted 

 with distilled water it was found that the transfusion of 

 hydrogen through it was so slow that it could not be detected 

 with the katharometer, even wdien the rate of flow of the air 

 past the fabric was reduced to as low a value as 2*4 litres 

 per hour. 



It was noted in the experiments on the transfusion of 

 hydrogen through soap films that as soon as the film became 

 thinner than the red-green stage the rate of diffusion rapidly 

 increased. It is evident, therefore, that the rate of diffusion 

 depends very largely on the thickness of the films used. In 

 the case of the wet cotton fabrics the thickness of the water 

 films filling up the interstices was very much greater than 

 that of the soap films investigated. 



XIII. Summary of Results. 



1. The rate of diffusion of hydrogen through a series of 

 balloon fabrics has been determined. 



2. The permeability of soap films whose thickness corre- 

 sponds to the red-green stage has been found for helium to 

 be 670 litres per square metre per day and for hydrogen 

 960 litres per square metre per day at 20° (J. 



3. The rate of transfusion of helium through soap films 

 has been shown to be 0*70 of that of hydrogen through 

 similar films. 



4. The diffusion of hydrogen through water films filling 

 the interstices of a wet cotton fabric has been shown to be 

 very low; with soap films showing interference colours the 

 rate of diffusion of both hydrogen and helium was found to 

 be considerable. 



The Physical Laboratory, 



University of Toronto. 

 May 15th, 1920. 



