APPENDIX B LXIII 



different points in the machine under equiHbrium conditions when the 

 gas was passed through it in various ways. As a result of this pro- 

 cedure it was soon found what parts of the machine could be eliminated 

 and what parts could be modified with advantage. When those 

 changes were made, which seemed desirable in the light of the experi- 

 ence gained, it was found that a machine had been evolved w^hich 

 would give highly satisfactory results. 



A sketch of the experimental machine as it was finally constructed 

 was exhibited. 



Miscellaneous Investigations 



In the course of the investigation on the development of a 

 machine for extracting helium from natural gas, supplies of helium 

 of varying degrees of purity became available. These were highly 

 purified, and were used for the investigation of certain collateral 

 problems which demanded solution. Among the results obtained it 

 was found that for aeronautical purposes hydrogen could be mixed 

 with helium to the extent of 15 per cent, without the mixture becoming 

 inflammable or explosive in air. Mixtures containing even as much 

 as 20 per cent, of hydrogen could be burnt or exploded only when 

 treated in an exceptional manner. The permeability of rubbered 

 balloon fabrics for helium was shown to be about 0.71 of its value for 

 hydrogen. For skin-lined fabrics the permeability to hydrogen and 

 helium was about the same. Thin soap films were found to be about 

 one hundred times more permeable to hydrogen and helium than 

 rubbered balloon fabrics, but untreated cotton fabrics, when wetted 

 with distilled water, were but feebly permeable to these gases. It 

 was found that rapid estimations of the amount of helium in a gas 

 mixture could be made with a pivoted silica balance, a Shakspear 

 katharometer or a Jamin interferometer. 



The latent heats of methane and ethane have been determined, 

 as has also the composition of the vapour and liquid phases of the 

 system methane-nitrogen. It has also been shown that helium con- 

 taining as much as 20 per cent, of air, oxygen, or nitrogen can be 

 highly purified in large quantities by simply passing it at slightly 

 above atmospheric pressure through a few tubes of cocoanut charcoal 

 kept at the temperature of liquid air. In the spectroscopy of the 

 ultraviolet helium has been found to be exceptionally useful. Arcs 

 in helium between tungsten terminals can be easily established and 

 maintained. In a particular investigation with a vacuum grating 



