Section III, 1919 [37] Trans. R.S.C. 



The Permeability of Balloon Fabrics to Hydrogen and to Helium ^ 



By R. T. Elworthy, B.Sc, and V. F. Murray, M.A., B.Sc. 



Presented by Professor J. C. McLennan, F.R.S. 



(Read May Meeting, 1919.) 



Introduction 



In view of the proposed use of helium in place of hydrogen for 

 filling airship envelopes, it became necessary to investigate the per- 

 meability of fabrics to this gas; and more especially to obtain the 

 ratio of the permeabilities to helium and to hydrogen of typical air- 

 ship fabrics. 



If it be assumed that the phenomenon of leakage through a 

 fabric can be classified as effusion, a leakage of helium 0-71 times 

 by volume that of hydrogen would be expected. If this ratio be 

 calculated by the Hugoniot-Reynolds formula for the adiabatic 

 efflux of a monatomic and a diatomic gas a value 0*75 is obtained. 



The passage of a gas through a rubbered or a skin-lined fabric is 

 not, however, a case of simple effusion, but is a more complex pheno- 

 menon. The solubility of the gas in the material may be a factor of 

 importance'^. 



Recently, Dewar' repeated the classical work of Graham on the 

 diffusion of gases through rubber membranes. Gases at varying 

 pressures and temperatures were allowed to diffuse through Para 

 rubber membranes 0-01 mm. thick into a vacuum. Relative rates of 

 diffusion were determined and are given in this paper as well as absolute 

 rates expressed in cubic centimetre per day per square centimetre. 

 Dewar found that the relative rates differed for different temperatures 

 and he states that "the order of diffusibility is difficult to associate 

 with any chemical or physical property." From his data the ratio 

 of the diffusibility of helium to that of hydrogen is 0-43 at 15-5°C. 



1 Communicated by Professor J. C. McLennan, F.R.S., by permission of tlie 

 Admiralty. 



2 Barr. Advisory Committee for Aeronautics. Permeability of Balloon Fabrics 

 by Helium. 1915. 



Edwards. U.S. Bureau of Standards. Tech. Paper 113. The Determination 

 of Permeability of Balloon Fabrics. 1918. 



' Dewar. Proc. Roy. Inst., pp. 813-26. 1918. 



