OF FLAMES CONTAINING SALT VAPOURS. 
517 
The explanation of the small inverse current when the E.M.F. is small is not easy. 
It was increased by the introduction of the head, which may have been due to some 
salt jDarticles getting carried round to the lower electrode by the circulation of the air 
between the electrodes. The presence of this inverse current prevented the E.M.F. 
necessary to bring down tlie negative ions being determined very exactly, as it varied 
with the size of the bead and with the volatility of the salt used. 
The P.D. required by the negative ions was about 1 volt for both oxy and haloid 
salts of any of the alkali metals. Taking the potential gradient corresponding to this 
as 0‘2 volt per centim. gives for the velocity of the negative ion due to 1 volt per 
centim. 
centims. 
1030 - , 
sec. 
which is 17 times the corresponding velocity of the positive ions. 
Diagram No. 14. 
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O 
QJ 
c:i 
r 
o 
s: 
§ 
'd 
.vV\ ^ 
r" — 
i - 
6 
A 
V / 
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-i 
jurrsn 
4———> 
5 with 
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i VO its 
Another method of estimating the velocities of tlie ions was alstj tried. Two 
electrodes of platinum foil were fixed opposite each other in the flame, about 1'5 
centim. apart, each electrode being I’5 centim. square. A bead of salt was held 
just below one of these, so that the salt vapour only came into contact with this 
electrode which was connected to earth. The ether electrode was charged, and any 
leak from it measured by the galvanometer. It was found that the current was not 
increased by the presence of the head of salt unless the E.M.F. used was greater 
than a definite amount, which was much greater when the electrode was negatively 
charged than when it was positively charged. This E.M.F. necessary for the current 
to increase when the salt is introduced is evidently that required to drag the ions 
from one electrode to the other, across the Idast of the flame gases. The salt vapour 
from the bead rapidly spreads out in the flame, so that unless the charged electrode 
was placed near the edge of the flame, the vapour came in contact with both elec- 
