773 



NATURE 



[August 19, 1920 



Helium: Its Production and Uses.^ 

 By Prof. J. C. McLennan, F.R.S. 



II.. 



Miscellaneous Investigations. 

 T 1*^ the course of the investig-ation on the de- 

 ^ velopment of a machine for extracting helium 

 from natural g-as, supplies of helium of varying 

 degrees of purity became available. These 

 were hig-hly purified, and used for the investiga- 

 tion of certain collateral problems which de- 

 manded 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 inflam- 

 mable 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 ex- 

 ceptional manner. The permeability of rubbered 

 balloon fabrics for helium was shown to be about 

 071 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 containing 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 

 coconut charcoal kept at the temperature of liquid 

 air. In the spectroscopy of the ultra-violet helium 

 has been found to be exceptionally useful. Arcs 

 in helium between tungsten terminals can be easily 

 established and maintained. In a particular inves- 

 tigation with a vacuum grating spectrograph, it 

 was found that by the use of arcs in helium under 

 30 cm. pressure illumination could be maintained 

 continuously for' hours, and with such arcs spectra 

 could easily be obtained extending to below 

 1000 A.U. 



Although it is known that free electrons can 

 exist in highly purified helium to an amount easily 

 measurable, it was found that pure helium undei 

 a pressure of more than 80 atmospheres did not 

 exhibit anything in the nature of metallic conduc- 

 tion. Moreover, the mobilities of both positive 

 and negative ions formed by a-rays in helium 

 under this high pressure were found to have about 

 one-third the value expected on the basis of an 

 inverse pressure law. 



1 From a lecture delivered before the Chemical Society on June j?. 

 Continued from p. 751. 



NO. 2651, VOL. 105] 



The Uses of Helium. 



The investigation into the problem of producing 

 helium in large quantities was originally under- 

 taken with a view to the utilisation of the gas in 

 aeronautical warfare. The investigation has shown 

 that it can be produced at a cost which is not 

 excessive, but it has also been shown that from 

 the sources in the Empire which are known and 

 have been examined the supply of helium cannot 

 be greater than about 12,000,000 cubic feet per 

 year. This quantity clearly would be sufficient to 

 keep only a very few of our airships of the larger 

 type in commission, even if the gas were diluted 

 to the extent of 15 per cent, with hydrogen. This 

 amount would, however, suffice to keep a number 

 of the smaller aircraft supplied. Moreover, it 

 might be used to fill fireproof compartments ad- 

 jacent to the engines if it were ever decided to 

 install these within the envelopes of our larger 

 airships. 



Since it has been demonstrated that helium can 

 be produced in quantity, one is led naturally to 

 consider in what directions one can hope to use 

 the gas other than that originally intended. In 

 industry it may be used as a filling for thermionic 

 amplifying valves of the ionisation type. It may 

 also be used for filling tungsten incandescent 

 filament lamps, especially for signalling purposes 

 where rapid dimming is an essential, and for pro- 

 ducing gas arc lamps in which tungsten terminals 

 are used, as in the " PointoHte " type. Both 

 these varieties of lamp possess the defect, how- 

 ever, of soon becoming dull owing to the ease with 

 which incandescent tungsten volatilises in helium 

 and deposits on the surface of the enclosing glass 

 bulbs. As regards illumination, helium arc lamps 

 possess an advantage over mercury arc lamps 

 in that the radiation emitted has strong inten- 

 sities in the red and yellow portions of the 

 spectrum. 



It has been shown by Nutting {Electrician, 

 March, 191 2) that Geissler tubes filled with helium 

 are eminently suitable, under certain conditions, 

 for light standards in spectrophotometry, but the 

 amount of the gas which could be used in this way 

 is very small. 



In spectroscopy, especially for investigations in 

 the ultra-violet region, helium is invaluable. 

 Doubtless its use in this field will be rapidly 

 extended. The use of the gas in physical labora- 

 tories generally, and especially where certain in- 

 vestigations on the properties of matter are carried 

 out, will also be greatly increased. 



It has recently been proposed to use hehum in 

 place of oil for surrounding the sv«itches and 

 circuit-breakers of high-tension electric transmis- 

 sion lines. If the gas should prove suitable for 

 this purpose, large quantities could be utilised, but 

 it has yet to be demonstrated (and it is not clear 



