﻿by Elements in the Electric Discharge- lube'. 223 



so it was concluded that some of the hydrogen assumes an 

 active modification under the action of the electric discharge, 

 and in this form it is able to form chemical compounds with 

 the sodium and the potassium present in the alloy. The U 

 tube in the enclosure at —40° C. excluded the possibility of 

 the action being due to the heat from the discharge-tube. 

 The white crystalline compound which first appears is a 

 mixture of the hydrides of sodium and potassium. The exact 

 nature of the greyish-coloured product formed afterwards is 

 unknown, but it is probably a solution of the hydrides in the 

 alloy. 



Water is evolved by an electric discharge when passed 

 through any vacuum vessel. It comes from the glass, and 

 would not be kept back by the trap cooled to —40° C; for 

 at that temperature water substance has a vapour-pressure of 

 about 0*1 mm. Hg. The presence of water-vapour " fouls " 

 the surface of the alloy, but this fouling gives a black 

 deposit on the surface which is quite different from the 

 white crystalline layer observed in the present experiments. 

 The black deposit consists of sub-oxides of sodium and 

 potassium, and its appearance has been noted previously 

 by the author *, although in rthat paper it was attributed to 

 the hydrides. It has now been proved by chemical analysis 

 that this black deposit does consist of the sub-oxides. 



Sulphur was tested in the following manner: — A small 

 piece of filter-paper, soaked in lead-acetate solution, was 

 placed together with a small amount of the solution in D. 

 The rest of the apparatus was separated from D by a mercury 

 cut-off not shown in the figure. C contained sulphur which 

 had been deposited in a thin film over the interior. After 

 exhausting the whole of the apparatus to a pressure of about 

 5 mm. of Hg., the mercury cut-off between C and D was 

 closed and the rest of the apparatus highly exhausted. 

 Hydrogen was then admitted to A until the pressure was 

 about 7 mm. Hg. While the electric discharge was passing, 

 the mercury cut-off was opened. This was repeated many 

 times, the pressure of the gas in A being gradually increased. 

 Each time communication with D was established, any 

 gaseous product formed in C was admitted to D. In the 

 course of a few minutes the paper soaked with the lead- 

 acetate solution turned black, showing the presence of a 

 sulphide of hydrogen. This chemical compound must have 

 been produced by the action of an active form of hydrogen 

 on the sulphur. The surface of the mercury at the cut-off 



* Proc. Roy. Soc. A. vol. xc. (1914). 



