of Electricity through Hot Gases. 445 



first when A was the positive and B the negative electrode; and, 

 secondly, when B was the positive and A the negative elec- 

 trode. No difference could, however, be observed between the 

 two cases. This is in striking contrast to the results of a 

 similar experiment made by Hankel (Wiedemann's Elektrici- 

 tdt, iv. p. 891) with different-sized electrodes immersed in a 

 flame ; for Hankel found that the deflexion of the galvano- 

 meter when the largest electrode was negative was greater 

 than when it was positive in the proportion of 294 to 34. 

 We must remember, however, that though a flame is no doubt 

 very hot gas, the condition of this gas is not nearly so simple 

 as that of the hot gas which was the subject of our experiments. 

 For, in the first place, the temperature of the flame varies 

 greatly from place to place, and, secondly, there seems to be 

 a separation of the electricities in the flame, so that the nega- 

 tive electricity is in one part of the flame and the positive in 

 another. In the hot gas with which we had to deal the 

 temperature was very much more uniform than in the case of a 

 flame, and there was no evidence of the positive electricity 

 being in one part of the gas and the negative in another, as is 

 the case in the flame : this separation of the electricities might 

 easily give rise to a want of symmetry in the conduction. 



Another way in which the symmetry of the conduction was 

 tested was by raising one electrode out of the hot gas and 

 keeping it out until it was cool, then suddenly plunging it 

 into the hot gas again. In this case it was found that there 

 was no conduction until both electrodes were glowing, how- 

 ever the signs of the hot and cold electrodes were changed. 

 The same thing was tried in a slightly different way by 

 having two earthenware crucibles at a white heat connected 

 by a strip of platinum foil with one electrode dipping into one 

 crucible and the other into the other; a gas which conducted 

 well was put into one crucible, while the other crucible con- 

 tained air. No difference in the deflexion of the galvanometer 

 could be detected when the signs of the electrodes were 

 reversed. 



Polarization. 



A great many experiments were made with various hot 

 gases, such as iodine, hydriodic acid, hydrochloric-acid gas, 

 and the vapours of sodium and potassium, to see if the passage 

 of the electricity through these gases produced any polarization 

 of the electrodes. The result of these experiments was that 

 when all the sources of disturbance were eliminated no effect 

 of this kind could be detected. In the first set of experi- 

 ments a commutator was used which first sent the current 

 through the gas, the galvanometer being out of circuit ; on 



