Disinter) rat ion of the Aluminium Catliode. 353 



seemed not much below that brought about by the mercury 

 vapour. 



Disintegration in Carbon Monoxide. — The carbon monoxide 

 was prepared from ferrocyanide o£ potassium and purified in 

 the usual way. Small portions of the gas were let in from 

 the annex tube of the type in fig. 2. Under the electric 

 discharge the cathode became covered in part with a brownish 

 coating, probably due to the separation of carbon from the 

 CO. As the discharge continued, the pressure fell rapidly, 

 and the CO seemed to be absorbed and to disappear. More 

 gas had to be let in several times, before any disintegration 

 was noticed, and after an hour or more only a small deposit 

 had been made. The presence of the carbon set free may 

 have retarded the rate of disintegration in this instance. 



Behaviour of the Cathode in Nitrous Oxide. — The nitrous 

 oxide was prepared from ammonium nitrate and purified. 

 The gas was let into the discharge-tube as in preceding cases. 

 "When the discharge was started the pressure fell rapidly, the 

 green fluorescence gradually disappeared, and in about ten 

 minutes the discharge refused to pass through the tube, and 

 jumped the gap at the spark terminals of the coil. A small 

 additional amount of gas was let in, and again the pressure 

 dropped, and in about ten or twelve minutes the discharge 

 refused to pass through the tube any longer. This procedure 

 was repeated some seven times, with the same result. No 

 disintegration took place, and it seemed useless to continue 

 the process. The cathode had become darkened near the 

 centre during the discharge, and some chemical action had 

 seemingly taken place between the cathode and the decom- 

 position products of the N 2 0. The N 2 gas, or its 

 decomposition products, exhibited a very vivid afterglow 

 when the discharge was turned off. The glow was of a 

 yellowish pink colour, and lasted for some seconds. The 

 glow may have been due to the " active nitrogen " studied by 

 Strutt *. 



Delayed Disintegration, — During the above study of the 

 disintegration of the aluminium cathode, sometimes the 

 deposition of the metallic mirror began almost as soon as 

 the discharge was started ; at other times the disintegration 

 began only after several hours of discharge. In one or two 

 instances, the discharge was sent through the tube for a long 

 time, with no deposition of a mirror apparent ; then the gas 

 in the tube was left exposed over night to the phosphorus- 

 pentoxide tube, and in the morning the disintegration began 



* Rov. Soc. Proc, Ser. A. lxxxv. p. 377 (1911) ; Ser. A. lxxxvi. p. 262 

 (1912). * 



Phil Mag. S. 6. Vol. 28. No. 165. Sept. 1914. 2 A 



