Behaviour of Metallic Vapours in Flames. 23 



Difference of potential between the electrodes = 100 volts. 



Pyrometer reading. 



Eadtatecl energy. 



Conductivity. 



1-98 



2-60 



37-0 



1-88 



1-15 



180 



1-85 



0-80 



140 



1-82 



0-60 



105 



1-78 



0-35 



65 



1-76 



0-25 



35 



All the measurements are in arbitrary units. 



The conductivity of the pure flame, which was naturally 

 always subtracted from the reading for the flame with salt, 

 was about 5 arbitrary units. 



The proportionality between conductivity and luminosity 

 (radiated light energy) is to be expected from the known 

 similarity between the laws connecting conductivity and 

 concentration of metal in the flame, and connecting light- 

 emission and concentration *. 



The fact that chlorine can destroy the luminosity of 

 metallic vapours in flame without much influencing the con- 

 ductivity t, can be explained by the action of the glowing 

 platinum electrodes, which, in the measurements in question, 

 stood in the body of the vapour. It is probable that the 

 impact of molecules of the chloride with one another is in- 

 effectual in the liberation of electrons, which is effected by the 

 impact of uncombined metallic atoms with one another : this 

 accounts for the lack of light-emission. On the other hand, 

 the impact of the chloride molecules on the glowing platinum 

 may suffice to liberate electrons ; it is probable that the 

 greater part of the conductivity is always due to liberation of 

 electrons at the surface of the electrodes, when they stand in 

 the vapour (see the experiments in § 3}. For a fuller dis- 

 cussion of these views see a paper by P. Lenard %, 



I propose making experiments on the effect of chlorine on 



* See Arrhenius, Ann. der Physik, xlii. p. 18 (1891), and Gouy, Ann. 

 de Chemie et de Physique [5] xviii. p. 1 (1879). 



t Snrithells, Dawson, and Wilson, Phil. Trans. A. cxciii. p. 89 (1900). 

 % P. Lenard, Sitzungsberichte der Heidelberger Academie, Dec. 1911. 



