Condensation of Vapour of Mercury on Selenium, 67 



May 11. — Dr. GKhither, M.A., Vice-President, in the Chair. 



The following communication was read : — 



" Condensation of Vapour of Mercury on Selenium in the Sprcngel 

 Vacuum." By R. J. Moss, P.C.S., Chemical Laboratory, Royal 

 Dublin Society. 



In the course of experiments on the electrical conductivity of sele- 

 nium, a cylindrical bar of this substance in the vitreous state was 

 enclosed in a glass tube which was attached to the exhaust-tube of 

 a Sprengel pump. The bar of selenium was 45 millims. long and 

 3*5 millims. in diameter. Platinum wares were attached to the 

 ends of it and passed through the sides of the glass tube. The 

 tube was exhausted, and allowed to remain attached to the pump 

 for four days. It was now found that the selenium had ac- 

 quired a conductivity greatly exceeding that of the pure element in 

 its most highly conducting condition. The experiment was re- 

 peated wdth the intention of observing the time required to produce 

 conductivity. In forty-two hours the needle of a highly sensitive 

 galvanometer was slightly deflected when the selenium was placed 

 in the circuit of ten Leclanche cells. The conductivity of the sele- 

 nium increased rapidly for four days, when the experiment was 

 unavoidably interrupted. On admitting air to the tube no change 

 of conductivity was observed. The selenium was unaltered in 

 appearance, even when examined microscopically. On breaking 

 the bar it was found that the conducting-film was entirely super- 

 ficial ; it was not removed by rubbing forcibly with a cloth. Dilute 

 nitric acid also failed to remove it. Bibulous paper moistened 

 with solution of silver ammonio-nitrate was not stained by it (Mer- 

 get, ' Comptes Eendus,' vol. lxxiii. p. 1356). It therefore appears 

 highly probable that the film does not consist of uncombined mer- 

 cury. As it has not hitherto been known that mercury combines 

 with selenium at ordinary temperatures, a bar of selenium was 

 immersed in mercury and allowed to remain undisturbed for six 

 months. At the end of this time it was found that the selenium 

 was coated with a highly conducting film. I could not detect any 

 difference between this film and those produced in the Sprengel 

 vacuum. An attempt w r as now made to estimate the quantity of 

 mercury required to produce the observed conductivity. A bar 

 of selenium 125 millims. long and 2 millims. in diameter, having 

 platinum wires fused into each end, was enclosed in a glass tube, 

 containing also a minute globule of mercury about # 5 millim. in 

 diameter. The tube was exhausted by means of the Sprengel pump, 

 and then hermetically sealed and detached from the pump. In 92 

 hours the bar began to conduct, and the conductivity increased 

 rapidly from day to day for four days. On the fifth day, no 

 increase being observed, it w T as supposed that air had leaked into 

 the tube ; and on examining it a flaw, which would account for the 

 leakage, w r as detected. The tube was therefore again attached to 

 the pump, exhausted, and again sealed, the defective portion being 



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