506 



Dr. R. S. Willows on the 



by means of a liquid rheostat placed in the circuit and shown 

 in fig. 2. Fio-. 2. 



This consisted of two fairly wide capillary 

 tubes having platinum wires fused into their 

 closed lower ends ; both limbs were nearly 

 filled with distilled water to which had been 

 added a small amount of impurity such as 

 KHO. Another platinum wire, bent twice at 

 right angles, could be moved up and down by 

 means of an insulating handle. The whole 

 w T as suitably supported and insulated on paraffin 

 blocks. 



In order to make the change in pressure 

 produced by the action of the discharge as 

 large as possible, the volume in communi- 

 cation with N must be reduced as much as it 

 can be ; hence, at the time of making an 

 experiment, taps B and E were closed and J 

 was cut off from N by means of a mercury 

 trap L. 



2. To give some idea of the magnitude of the effects, the 

 following numbers are given : — The volume of the tube N, 

 gauge and connexions was in most cases about 100 c. c, 

 and 223 divisions on the gauge represented a millimetre 

 pressure. With a current of about 10*8 x 10 -4 amperes passing 

 for half an hour, a decrease in pressure of from 10 to 40 gauge- 

 divisions took place, the amount depending on the pressure. 



Thus in a case where the volume was 108 c. c. and 

 pressure about 1 mm., a current of 10*8 X 10 -4 amperes 

 running for thirty minutes produced an alteration in pressure 

 of twenty scale-divisions, or a reduction of T y mm « nearly. 

 From this it can be found that in this case the passage of 

 3*888 coulombs of electricity causes '013 c. c. of gas reduced 

 to 760 mm. pressure to disappear. 



When different currents were tried, it was found that the 

 amount of gas that disappeared increased more rapidly than 

 the current. 



The chief difficulty met with was the trouble experienced in 

 getting the electrodes quite clear of gas. In most cases in which 

 aluminium- wire electrodes were used, it was found necessary 

 to pass a strong current for at least twenty hours before regular 

 measurements could be obtained ; in several cases the tube 

 near the cathode was too hot to be touched with the fingers, 

 and it was kept in this state for several hours at a time. 



In one case in which hydrogen was used, thirty hours of this 

 treatment was insufficient to eject all the gas from the electrodes. 



In the earlier experiments it was found that, starting from 



