OF FLAMES CONTAINING SALT VAPOURS. 
523 
The rate at which the current increased with the P.D. after the least necessary 
P.D. was reached varied greatly with different salts, and with the sign of the charge 
on the grating. In general, the salt which was the more volatile gave the greater 
rate of increase of current with P.D. The rate of increase of current with P.D. was 
also usually greater when the grating was negatively charged than when it was 
positively charged. 
When the grating was negatively charged it was found that the P.D. at which the 
current began to increase with the P.D. between the electrodes was, other conditions 
remaining unchanged, aj^proximately 7’0 volts for all the salts tried, viz. :— 
NaoCOs, NaOH, NaCL, K^COa, KOH, KCL, KBr, KI, KF, LiCL, 
LLCO 3 , PbCL, EDCOa, CsCL, Cs,C 03 , CaCL,, BaCL,, SrCL,, Ba(N 03 )o. 
The following salts were also tried, but although they gave a large amount of 
current, it was so unsteady and lasted such a short time, owing to the decomposition 
of the salt, that no definite results could be obtained : FeCLg, AICL3, ZnOL^, MgCL.j. 
When the grating was positively charged, the least necessary P.D. was very 
approximately 25 volts with each of the salts of Li, Na, K, Ptb, and Cs mentioned 
above, and very approximately 48 volts for each of the salts of Ca, Sr, and Ba. 
The mean velocity of the air blast was estimated to be about 180 which 
sec. 
gives for the velocities of the ions due to one volt per centim. the following values :— 
( 1 .) Negative ions. 
(2.) Positive ions of salts of Li, Na, K, Eh, and Cs . 
(3.) Positive ions of salts of Ba, Sr, and Ca .... 
Only the relative value of these velocities has any pretensions to accuracy. As 
already explained, it was not found possible to obtain more than the order of 
magnitude of the absolute velocities. 
The result obtained for the velocities of the ions in the flame, viz., that all the 
negative have the same velocity, and likewise the positive ions of salts of Li, Na, K, 
Eb, and Cs, was thus found to hold good also in hot air. 
The velocities in the hot air are much smaller than those in the flame. The values 
given for the velocities in the hot air were obtained by assuming the fall of potential 
between the grating and the ring electrodes to be uniform. Since there was practi¬ 
cally no current between them up to the least necessary P.D., this assumption cannot 
be very far from correct; still, any departure from a uniform fall would cause the 
values given to be too small.* 
* Since the salt vapour is not ionised till it reaches the hot gauze, there are no ions between the gauze 
and flange ludess the ions go against the blast. 
26 
7-2 
3-8 
centims. 
sec. 
centims. 
sec. 
centims. 
sec. 
3x2 
