ELECTRICAL CONDUCTIVITY OF AIR AND SALT VAPOURS. 
425 
Current (1 
= 10-" 
ampere). 
500°. 
700°. 
900°. 
o 
o 
o 
1300° 
40 volts . 
. . 0-2 
0-3 
0-3 
0-9 
2-5 
100 „ . 
. . 5T 
5-5 
5-5 
6-8 
9-2 
800 „ . 
. . 7-0 
30-0 
45-0 
35-0 
71-0 
We see that for small E.M.F.’s the current increases very slowly at first, and then 
more rapidly. At higher E.M.F.’s it becomes nearly constant at 500°, whereas at 
1300° it is nearly proportional to the E.M.F. 
Diagram No. 5 shows the variation of the current with the E.M.F. for KI at 
1200 °. 
3. Vanation of the Current through Air with the Temperature. 
To determine the variation of the conductivity with the temperature at constant 
E.M.F., a series of measurements of the current due to a fixed number of cells at 
different temperatures was made. The value of the curi'ent was not read until it 
had become constant. A temperature reading was always taken both before and 
after the measurement of the current, and unless the two readings agreed the 
measurement was rej^eated. Usually no difficulty was experienced in keeping the 
temperature sufficiently constant, owing to the excellent working of the regulating 
arrangements on the gas and air supplies. The highest temperature was done first 
and the temperature then diminished by steps until the current became inappreciable, 
when the temperature was raised again and some of the observations repeated. 
The usual current of air coming from the sprayer was always passed through the 
tube, since it served to keep the inner electrode at nearly the same temperature as 
the outer one. Measurements of this kind, using air alone, were made from time to 
time during the course of the investigation, and, as already mentioned, it was found 
that a marked falling off in the conductivity at any particular temperature occurred 
as the tube got aged. 
VOL. CXCVJI.—A. 3 I 
