524 Dr. 0. Ludeking on the Action of the 



> J. J. Thomson (Phil. Mag. [5] xxix. pp. 358 & 441, 1890) 

 finds that hydriodic-acid vapour is an excellent conductor 

 of electricity. He experimented by passing the vapours of 

 his substances through a platinum tube heated to a yellow 

 heat and having in it platinum electrodes. It is not impos- 

 sible that we have here in part a true electrolytic decom- 

 position, and that in amount it is in direct proportion to the 

 conducting power. 



A pure gas is, I think, not electrolytically decomposed on 

 the passage of the first spark, and is practically a non- 

 conductor. However, by the passage of the first spark there 

 is produced by thermal dissociation a mixture of gases in the 

 pathway of the discharge. This it is that conducts fairly well, 

 so that then electrolysis may take place. The conduction of 

 the current is therefore not simultaneous with the passage of 

 the spark, and takes place only during a short time. Conse- 

 quently the electrolytic and thermal dissociations are not 

 simultaneous. The partial pressures of the substances elec- 

 trolysed would thus be reduced, another factor in the pro- 

 motion of electrolytic conduction. 



This may be proved experimentally: — By taking a mixture 

 of the original gas and its components it is possible to effect 

 an electrolytic decomposition by means of the Ruhmkorff coil 

 without the passage of any spark. Such a mixture was pre- 

 pared, and the electrodes so adjusted that no spark could pass. 

 Then what seems to be an electrolysis was effected, iodine 

 being deposited on the positive pole. That this iodine was 

 not free iodine of the mixture was proved by leaving it out 

 entirely, and making instead a mixture of hydrochloric acid, 

 hydriodic acid, and hydrogen. Then the same phenomenon 

 was observed. 



We are therefore justified in the conclusion, arrived at also 

 by E, Wiedemann and J. J. Thomson, that the decomposition 

 is in part a true electrolysis after the manner of a Grrotthus 

 chain. At least this is one interpretation we may give for the 

 present. 



We have therefore to do with an imperfect insulator, and 

 the electrostatic energy is gradually transferred between the 

 poles. It is necessary that the electromotive force should be 

 sufficient to decompose the chemical compound, as otherwise 

 no decomposition could have place, but only conduction. It 

 would seem, further, that Thomson's view is correct — that 

 the ease of decomposition of the molecule into atoms is pro- 

 portional to the conducting power. In that gases at ordinary 

 temperatures are such very poor conductors, it would seem 

 that the conductivity is, as I stated above, the result of 



