466 
Proceedings of Poycd Society of Edinburgh. 
SESS. 
On the Electrification of Air by Uranium and its Com- 
pounds. By J. Carruthers Beattie, D.Sc. With a Note 
by Lord Kelvin, G.C.Y.O., F.R.S., etc. etc. 
(Read June 7, 1897.) 
§ 1. It is proposed in the following paper to describe experiments 
made to test the electric state of the air in the neighbourhood of 
metallic uranium, or of other metals on which a salt of uranium 
had been deposited from a solution, when these were charged to a 
positive or a negative potential. 
§ 2. Method employed. To test the electric state of the air the 
electric filter method* due to Kelvin, Maclean, and Galt was em- 
ployed. The special filter used in the experiments to he described 
was a block- tin pipe, 10 cms. long and 1 cm. diameter, filled with 
brass filings. This was insulated on two tunnelled pieces of paraf- 
fin, and put in metallic connection with the insulated pair of 
quadrants of a quadrant electrometer. From one of the tunnelled 
pieces of paraffin a metal tube led to an air pump ; from the other 
a piece of india-rubber tubing led to the place where the air to be 
tested was. This air was then drawn through the electric filter, 
and the deviation from the metallic zero of the electrometer, when 
the two pairs of quadrants were insulated, was noted. To give some 
idea of the efficiency of the filter, the results obtained when air 
was pumped away from the neighbourhood of the electrodes of a 
RuhmkorfF inductorium (Apps. pattern, 10-inch spark) will be 
given. 
When the electrodes were near enough to admit of sparks passing 
it was found that air, drawn from the immediate neighbourhood of 
the positive electrode, gave a positive electrification of +1*5 volts on 
the electrometer after one minute of pumping at the rate of twelve 
strokes per minute. When the air was drawn from the immediate 
neighbourhood of the negative electrode, a negative electrification 
of - 2 5 volts in half a minute was observed. 
* Proc. Roy. Soc. (London), March 14, 1895. 
