682 



SCIENCE 



[N. S. Vol. XLI. No. 1062 



As a result of this investigation at first hand, 

 Dr. Foster was convinced that Dr. Knowlton 

 and the other men of the faculty at Salt Lake 

 City have assumed no greater freedom of 

 speech than every member of the Eeed College 

 faculty has as a matter of course. 



DISCUSSION AND COSBESPONDENCE 



ON THE PRODUCTION OF RAEE GASES IN VACUUM 



TUBES 



To THE Editor of Science: A number of 

 investigators, among them Sir J. J. Thomson, 

 Sir W. Eamsay, Winchester, and Collie, have 

 found that helium and neon are produced in 

 vacuum tubes by electrical discharges. These 

 gases veere not accompanied by argon, and 

 therefore not due to leaks in the apparatus.^ 

 A thoroughly satisfactory explanation of the 

 appearance of the gases remains to be given, 

 although a very plausible hypothesis has been 

 advanced by Professor Winchester. Winches- 

 ter^ finds that helium and neon are given 

 off from aluminium electrodes only during the 

 first few hours of long-continued discharges, 

 and he therefore concludes that the gases must 

 have been occluded on the surfaces from the 

 atmosphere. 



This explanation agrees with a number of 

 facts. For example, we may explain a second 

 liberation of heliimi and neon, sometimes 

 noticed in vacuum tubes after many hours' 

 continuous running, by supposing that a sur- 

 face layer (e. g., slag), imbedded in the metal 

 when it was poured, becomes exposed when the 

 electrode is partly " spluttered " away. The non- 

 appearance of these gases when very heavy 

 discharges (i. e., large currents) are used, as 

 in one experiment with uranium, by Collie,^ 

 would mean that the surface layer is spluttered 

 away before any considerable amount of gas 

 has been liberated. 



There is an alternative explanation which 



1 T. E. Merton, Eoy. Soe., Froo., Ser. A, 90, pp. 

 549-53, August 1, 1914. 



zG. "Winchester, Phys. Bev., N. S., Vol. 3, pp. 

 287-94, April, 1914. 



3 J. N. Collie, Boy. Soc, Proc, Ser. A, 90, pp. 

 554-56, August 1, 1914. 



fits the facts equally well, if we admit the 

 possibility of changes of a radioactive nature 

 taking place in an ordinary vacuum tube. 

 But there is, in the first place, no good evi- 

 dence that ordinary inactive matter can be 

 transformed by the radiations of radioactive 

 substances;* and consequently, in view of the 

 great energy of the a particles, there is reason 

 for supposing that the swiftest ions in a 

 vacuum tube are equally incapable of produc- 

 ing disintegration of atoms (or rather, ac- 

 cording to recent views, disintegration of 

 nuclei; the resultant positive charge upon 

 which determines the chemical properties of 

 atoms^) — unless, perhaps, there were present in 

 the tube enormous differences of potential. 

 Nevertheless, in an experiment by Sir W. 

 Eamsay," evidence is given which suggests 

 an inter-relationship between the elements 

 helium, neon and oxygen. 



Certain experiments performed by the 

 writer upon the conduction of electricity at 

 contacts of dissimilar solids^ show that, how- 

 ever carefully a metal may be cleaned in air, 

 or in pure electrolytic oxygen, a surface film 

 remains, sufficient to give electrical properties 

 to such a surface, markedly different from 

 those obtaining upon a surface that is cleaned 

 mechanically in vacuo, or in pure electrolytic 

 hydrogen. This being the case, it is seen that 

 all electrodes hitherto employed in the produc- 

 tion of rare gases have had a layer of oxide on 

 the surface — traces of which must have re- 

 mained imtil all the original surface had been 

 removed by the action of the discharge. 



In view of this fact it seems desirable that 

 a tube be constructed, with electrodes similar 

 to those used by Winchester^ (which were 

 found to liberate the gases rapidly) ; it being 

 possible to clean these electrodes on all sides, 



i Eutherf ord, ' ' Eadioactive Substances and their 

 Eadiations," 1913, §116. 



5 Eutherford, Phil. Mag., Vol. 27, 6 ser., pp. 

 488-98, March, 1914. 



6 Sir W. Eamsay, Collie, and Patterson, Nature, 

 Vol. 90, p. 653, February 13, 1913. 



7 E. H. Goddard, Phys. Bev., Vol. 28, No. 6, pp. 

 405-28, June, 1909. 



8 Winchester, loo. cit. 



