[ 441 ] 



XL VIII. On the Passage of Electricity through Hot Gases. 

 By J. J. Thomson, M. A. , F.E.S., Cavendish Professor of 

 Experimental Physics, Cambridge. 



[Continued from p. 366]. 



Conductivity of Hot Metallic Vapours. 



TO vaporize such metals as silver or tin a higher tempera- 

 ture is required than can be produced by the arrange- 

 ment which sufficed for the substances hitherto described. 

 The method used to determine the conductivity of metallic 

 vapours was as follows: — In a brick made of " ganister" a 

 vertical channel was bored, into which an earthenware crucible 

 w^as placed : this vertical channel was in communication with 

 a horizontal one which conveyed the flame of a large oxy- 

 hydrogen blowpipe. The terminals conveying the current 

 dipped into the crucible, which was kept full of nitrogen 

 when the metal used was one that readily oxydized. In this 

 furnace silver could be volatilized, and the electrical conduc- 

 tivity of it and most of the metals more volatile than it were 

 tested. 



The metals tried were sodium, potassium, thallium, cad- 

 mium, mercury, bismuth, lead, aluminium, magnesium, tin, 

 zinc, and silver. Of these the vapours of mercury, tin, and 

 thallium did not seem to conduct at all ; at any rate their con- 

 ductivity is less than that of air ; the vapours of the other 

 metals conducted very much better than air, the best con- 

 ductors being the vapours of sodium and potassium, which 

 conducted even better than iodine. 



The difference between the behaviour of the vapours of 

 mercury, tin, and thallium and that of the other metallic 

 vapours is very remarkable. I thought at first it was con- 

 nected with the behaviour of the salts of these metals when 

 used as electrolytes, as the chlorides of mercury are such bad 

 conductors as hardly to deserve the name of electrolytes, while 

 one of the chlorides of tin is a non-conductor ; however, Mr. 

 T. 0. Fitzpatrick, who kindly determined for me the con- 

 ductivity of thallium chloride, found that it w T as normal, so 

 that the behaviour of the metallic vapours does not seem neces- 

 sarily connected with the conductivity of the salts of the metal. 



The vapour-densities of most of the metals seem to show 

 that the molecules of metals are monatomic ; if we suppose 

 the atom is able to possess and give up a charge of electricity, 

 this fact would explain the conductivity of their vapours. 



If tin and thallium were found to be exceptions to the rule 

 that the molecule of a metal is monatomic their want of con- 

 ductivity would be explained. The vapour-density oi' mercury 

 shows that if its molecule is diatomic all the compounds of 



Phil. Mag. S. 5. Vol. 29. No. 180. May 1890. 2 L 



