LUMINOSITY OF FLAMES CONTAINING SALT VAPOURS. 
77 
experiments the current, due to a constant P.D., between two platinum electrodes 
near together in the flame, was taken as a measure of the conductivity. 
The relation Y = Acd + Bc 2 shows that when the electrodes are near together and 
the term A cd therefore small, the current depends mainly on the fall of potential at 
the negative electrode which is represented by Be 2 . 
The .conductivity of the flame in the uniform potential gradient between the 
electrodes has little influence on the current when the electrodes are near together. 
It seemed likely that measurements of the conductivity, as measured by the ratio 
of the current to the uniform potential gradient, away from the negative electrode, 
might give simpler and more easily interpreted results than those previously obtained. 
The apparatus described in the preceding section of this paper was used. The 
same current was passed through two similar flames and the ratio of the uniform 
potential gradients in them measured. The amount of salt in one flame was kept 
constant and that in the other varied. In this way the ratios of the conductivities 
of the second flame, with different amounts of salt in it, were found. The first flame 
merely served as a standard with which to compare the second one. It was not 
assumed that the two flames had equal conductivities when solutions of equal 
strength were sprayed into them, although this was roughly true. Variations in the 
gas and air supplies probably affected both flames nearly equally, and therefore 
had little effect on the results obtained. 
The following results were obtained with solutions of caesium chloride :— 
Solutions sprayed 
Ratio of 
(grammes CsCl per litre). 
conductivities. 
Flame A. 
Flame B. 
B/A. 
20 ■ 2 (RbCl) 
80 
3-13 
20-2 (RbCl) 
8 
1-00 
20-2 (RbCl) 
0-8 
0-301 
0*08 
0-016 
0-535 
0-08 
0-032 
0-813 
0-08 
0-08 
1-37 
0-08 
0-16 
1-92 
0 
0 
1-00 
0 
0-0032 
2-88 
0 
0-008 
5-72 
0 
0-016 
8-90 
0-8 
0-8 
0-75 
0-8 
0-08 
0-21 
