Hydrogen and some of its Compounds. 371 



of the most important in physical science ; for it proves, 

 1 believe, incontestably that hydrogen cannot be a conductor. 



Professor Dewar has also shown that liquid hydrogen is an 

 insulator. The experiment sometimes shown, in which a 

 wire, rendered incandescent by a current of electricity and 

 surrounded by an atmosphere of carbonic dioxide, is suddenly 

 diminished in brilliancy by supplanting this atmosphere by 

 one of hydrogen, can be explained, in my opinion, not by the 

 better conductibility of hydrogen for heat, but by the in- 

 creased resistance of platinum due to the occlusion of this 

 gas by platinum. A palladium wire increases often as much 

 as 50 per cent, by the occlusion of hydrogen ; and a platinum 

 wire also shows a similar increase of resistance. 



The increased length of the electric spark in an atmosphere 

 of hydrogen is not due to an increased conductibility, but to 

 a dissociation of water-vapour which is analogous to the 

 dissociation which takes place in a voltaic cell. 



These are some of the facts which lead me to believe that 

 hydrogen is an insulator, and that water-vapour therefore 

 plays a controlling part in the passage of electricity through 

 gases. 1 am conscious that the conclusions in this paper are 

 somewhat radical, and I have, therefore, worked assiduously 

 during the past three years to test them in every way which 

 my mind suggested ; for it is not probable that many investi- 

 gators have at present twenty-thousand storage-cells which 

 would enable them to repeat my experiments. The strength 

 of currents and the voltage I have employed have certainly 

 reached the limit of glass tubes to withstand such powerful 

 discharges. The form of tube figured in my previous article* 

 is the only one which I have found capable of withstanding 

 steady currents of one-tenth to one-fifth of an ampere, and 

 instantaneous condenser discharges of many hundred amperes. 



The great advantage of the use of a storage-battery over 

 the employment of a RuhmkorfT coil in the study of the 

 ionization and molinization of gases is now generally recog- 

 nized. This advantage is forcibly seen in the first experiment 

 which I will bring forward in support of my view of the 

 importance of the role played by water-vapour in the passage 

 of electricity through gases. A wide tube, of the type I have 

 referred to, the narrow portion being approximately 1 centi- 

 metre, was provided with massive copper ring electrodes, 

 1 inch in outside diameter and one-eighth of an inch thick, 

 which were heavily electroplated with copper in order to 

 avoid the impurities of commercial copper. The glass tubes 



* Phil. Mag. Sept. 19C0. 



