42 



THE ROYAL SOCIETY OF CANADA 



(/) Fabrics 



The airship fabrics tested were supplied by the Department of 

 Aircraft Production of the Admiralty, and are described in Table I 

 (given below). Laboratory Reference Numbers are given in Column 

 I of the Table. 



The date of manufacture of the fabrics was not known. 



The test-pieces were cut from the roll, choice being made of a 

 portion of the fabric free from seams or apparent defects, and inserted 

 in the permeameter without any preliminary drying or dessication. 



Table I 



Measurement of Permeability 



It has already been stated that two distinct methods were em- 

 ployed in these experiments to determine the amount of gas diffusing 

 into the air through the sample of fabric. 



(a) In the first method, the hydrogen or helium in the air was 

 estimated by means of a Jamin interferometer, used in the manner 

 described in another paper^ 



The general procedure adopted was (i) to establish the rates of 

 flow of gas and of air, then, after an equilibrium condition in the 

 permeameter had been attained, (ii) to take readings of the percentage 

 of gas in the air at equal intervals of time over a period of about one 

 hour. The rate of flow of air was given by a gas meter which was read 

 at the beginning and end of the period. Intermediate readings vvere 

 also taken to check the uniformity of the air flow. 



^ McLennan and Elworthy. Proc. Roy. Soc. of Canada, 1919. 



