352 Mr. L. L. Campbell on 



hindering effect o£ the aluminium iodide formed. The 

 current strength employed was from 4 to 5 milliamperes. 



The size and form of the tube and of the cathode seem to 

 influence the voltage required to bring about this disinte- 

 gration of the cathode. 



Disintegration in Cyanogen. — The cyanogen, (CN) 2 , was 

 prepared by gently heating silver cyanide, AgCN, in the 

 annex tube, X, fig. 1. Under the electric discharge the 

 (GN) 2 changed to paracyanogen a?(ON), and other portions 

 were probably changed to C and N, while a portion of the 

 (CN) 2 remained undecomposed. When the cathode dark- 

 space had reached the walls of the tube opposite the cathode, 

 disintegration of the cathode set in, but was not so rapid as 

 was the case with any of the halogens. On portions of the 

 tube, not covered by the metallic mirror deposit, was found 

 a brownish deposit of carbon, with probably some para- 

 cyanogen. 



Disintegration in Pentane. — Pentane, C(CH 3 ) 4 , was chosen 

 as a typical and fairly stable hydrocarbon. The vapour of 

 the pentane was supplied to the discharge-tube by means of 

 an annex tube shown in fig. 2. When the cathode dark-space 

 had reached the walls of the tube, disintegration of the 

 cathode began, but the process seemed somewhat hindered by 

 decomposition products brought into existence by the dis- 

 charge. A deposit of carbon was found on those parts of 

 the walls of the tube where there was no metallic mirror 

 formed. 



Disintegration in Mercury Dimethyl. — The mercury di- 

 methyl, Hg(CH 3 ) 2 , was placed in an annex tube of type 

 shown in fig. 2. The vapour was soon partly decomposed by 

 the discharge, as was shown by the presence of mercury 

 spectrum lines. The disintegration of the cathode was quite 

 rapid, and was attended by a deposit of carbon on the tube, 

 as was the case when pentane was used. The mercury set 

 free from the dimethyl was probably the active agent that 

 brought about the disintegration of the cathode. 



Disintegration in Mercury Vapour. — Vapour of mercury was 

 let in from the annex tube in small quantity, and the disinte- 

 gration of the cathode in the presence of this vapour was 

 probably the most violent of any observed. 



Disintegration in Cadmium Vapour. — Finely ground cad- 

 mium metal was placed in an annex tube. Beneath the 

 bulb containing the metal was placed a small gas-flame that 

 melted the cadmium and kept a small supply of the metallic 

 vapour in the discharge-tube. In the presence of this vapour 

 the cathode disintegrated rapidly, and the rate of deposition 



