274 Prof. McLennan and Mr. Shaver on Permeability of 



been well established that the curve obtained by plotting 

 galvanometer deflexions against percentages of hydrogen or 

 helium present in air was a straight line through the origin. 

 The calibration showed that (1) 259 mm. deflexion on the 

 scale 1 metre from the galvanometer represented 1 per cent, 

 hydrogen in air, and (2) 163 mm. deflexion on the scale 

 1 metre from the galvanometer represented 1 per cent, of 

 helium in air. 



The following table gives a comparison of the results 

 obtained in the present experiments with those obtained by 

 Elworthy and Murray when using the same fabrics. In 

 each case the permeability is given as being the number of 

 litres of gas permeating 1 square metre of a fabric in 

 24 hours : — 







Table I, 









Results obtained in tbis 

 investigation. Temp. 20° C. 



Results obtaii 

 and Murray. 



led by Elwortby 

 Temp. 15°-5 0. 



Fabric No. 



Method I. 



Using 

 Katharoineter. 



Method II. 



Using 



Katharometer. 



Method I. 



Using 



Interferometer. 



Method II. 



Using 



Katharometer. 



*II.B 



96 



9-8 



8-4 



9-5 



III. A ... 



84 



8-0 







8-6 



IV 



5-0 





5-5 



4-7 



V.B 



63 





67 



6-4 



VI.A ... 



8-0 







8-1 



VI. C 



7-8 



7-5 





8-1 



XII 



5-4 



... 



.. . 





IV. Permeability of Films. 



After the preliminary experiments had been made, an 

 attempt was made to employ the same method in making a 

 determination of the transfusion of hydrogen and of helium 

 through a soap film. Sir James Dewar f in a paper presented 

 at a meeting of the Royal Institution of Great Britain in 

 Jan. 1917, described many interesting experiments with 

 long-lived soap bubbles and films, among them being a 

 determination of what he calls " gas transference " through 



* The fabric numbers refer to samples of balloon fabrics described in the 

 papers by Elwortby and Murray. 



t Dewar, Paper, " Soap Bubbles of Long Duration," presented at 

 weekly meeting of the Royal Institution of Great Britain, Jan. 19, 1917. 



