The Discharge of Electricity through Gases. 



535 



to small traces of foreign gases or to the state of surface of the 

 electrode. 



The modifications of the disruptive discharge between platinum 

 electrodes, which have been studied by Wiedemann and Ebert,* 

 deserve to be mentioned, but they depend on too many circumstances 

 to help us in deciding the question as to the possible effects of 

 chemical action at the surface of the electrodes. In order to obtain 

 an insight into these questions, it seems better to study the discharges 

 produced by radiation in cases where naturally a discharge would 

 not occur. This will probably lead to a simpler result than an in- 

 vestigation of the modification by radiation of a discharge inde- 

 pendently produced. The interesting facts discovered by Lenard and 

 Wolf will be mentioned in connexion with another part of our subject. 



Discharges through Flames. 



It was discovered by Paul Ermanf towards the beginning of this 

 century that a flame may conduct, and that a wire placed inside it 

 discharges positive electricity more easily than negative electricity. 

 BufPJ found that even the gases rising from a flame behave as con- 

 ductors of electricity, and Griese has carefully examined the behaviour 

 of these gases. He was thereby led, as has already been mentioned, 

 to the theory of electrolytic convection. It seems indeed impossible 

 to draw a different conclusion. We may assume that in a flame a 

 certain proportion of dissociated ions are present, some of which can 

 escape combination with each other for some time. As the gases rise 

 from the flame they will remain conductors until the recombination 

 of ions is complete, and this may take some time. According to 

 Giese, the gases may preserve their conductivity for some minutes. 



Dissociation alone, it must be remembered, is not sufficient to 

 convert a gas into a conductor. Thus, when owing to increased tem- 

 perature the molecules of iodine vapour split up, the atoms do not 

 necessarily behave as ions, for they are probably unelectrified. We 

 must imagine each iodine atom in the molecule to possess two 

 charges, and as dissociation proceeds a re-arrangement of the charges 

 takes place, so that the free atom will still carry two equal but now 

 opposite charges. 



Discharge through Gases in the Sensitive State. 



It is convenient to say that a gas is in its sensitive state as regards 

 electric stress when any electromotive force, however small, pro- 



* ' Wiedemann, Annalen,' vol. 33, p. 241 (1888). 

 f « Gilbert, Annalen,' vol. 11, p. 150 (1802). 

 X 'Annalen der Chemie,' vol. 80, p. 1 (1851). 



