OF FLAMES CONTAINING SALT VAPOUES. 
521 
nately, it is not possible to get anything more than rough estimates of these 
quantities. All that was attempted, therefore, was to determine the necessary P.D.’s 
for various ions under the same conditions. This gives the relative values of their 
velocities in the hot air. 
The following diagram shows the variation of the current with the P.D. when the 
platinum flange and the grating electrode were I centim. apart, the grating being 
positively charged with beads of KI and KOH :— 
Diagram No. 15. 
It will be observed that in each case the current is zero until a P.D. of about 
25 volts, is reached, when it increases nearly uniformly with the P.D. 
Other conditions remaining the same, the necessary P.D. should vary directly as 
the distance between the electrodes. Actually it was found that the necessary P.D. 
increased more rapidly than the distance, except when this was less than about 
1'5 centim. Below 1'5 centim. distance, the necessary P.D. varied as the distance 
between the electrodes. Thus the following results were obtained with a lib^COs 
bead:— 
Distance between 
Electrodes. 
Necessary P.D, 
centims. 
cells 
1-5 
17-5 
1-0 
12-5 
0-8 
9-5 
With other salts similar results were obtained. In most of the measurements made 
the grating and the flange were kept 1 centim. apart. 
The effect of varying the velocity of the air blast was also tried. It was found that 
for small variations of the velocity not greater than 20 per cent, of its usual value, 
the necessary P.D. varied directly as the velocity of the blast. The blast could not 
be increased more than about 20 per cent, with the apparatus available. For diminu- 
VOL. cxcn.— A. 3 X 
