ELECTRICAL CONDUCTIVITY OF AIR AND SALT VAPOURS. 
437 
Appendix. 
Added August U, 1901. 
Since writing the above paper I have made measurements with a slightly modified 
apparatus on a number of other salts of the alkali metals. The modifications made 
in the apparatus were not important. A separate galvanometer was provided for the 
thermo-couple, so that the temperature and conductivity could he observed simul¬ 
taneously, and the length of the platinum tube was increased liy 12 centims. to 
further insure that the current of air should have time to take up the temperature of 
the tube. The sprayer nozzle had to he readjusted, which considerably increased 
the amount of salt passing through the tube. With these exceptions the apparatus 
was practically identical with that described above. 
Measurements were made with salts of tiie alkali metals besides those of potassium, 
so far only used. 
At temperatures approaching 1300° the current E.M.F. curves for most salts 
resemble that given above for KI at 1200°. Below 1100° the current is almost 
always greater when the outer tube is negative, as already pointed out. However, 
above this temperature it has been found that the two-current E.M.F. curves cross 
each other, so that the current is then the greater at high E.M.F.’s when the outei- 
tube is positive. 
The following table gives the currents observed when a 1 per cent, solution of 
CsCl was being sprayed at a temperature of 1340° C. 
Current (amperes). 
r.D. 
Volts. 
Cuter tube -. 
Outei' tube +. 
1200 
8-80 X 10“^ 
15-10 X 10' 
800 
8'65 
13-LO „ 
600 
8-80 
9-30 
400 
7-62 „ 
4-25 
200 
2-34 „ 
1-14 „ 
120 
0-93 ., 
0-46 
40 
0-23 „ 
0-12 ., 
These results are typical of the behaviour of most alkali metal salts. 
It was found that with many salts on first applying the P.D. the current was often 
abnormally great for a short time, and then settled down rapidly to a steady value, 
ju-st as it does for air. KI, KCl, and other easily volatile salts only show this effect 
very slightly, so that as these salts were mainly used in the exiieriments described 
above, this effect was not observed with salts until after the above paper was 
written. 
