REQUIRED TO PRODUCE DISCM.\l;<;K THROUGH VAKIOUS GASES. 



37 U 



The arrangement is represented in fig. 1. A, B, are the ebonite discs, into the 

 fronts of which the brass sparking plates are let. These latter are not visible in the 

 figure. The elxmite plates are held together by the three screws c, d, e. The small 

 distance between them is equal to the thickness of the distance pieces. The leading 

 wires pass to the plates at /and tj, 



Fig. 1. 



This whole arrangement is enclosed in the cylindrical glass pot M, shown separately 

 for the sake of clearness. M has a broad ground flange S, which is covered by the 

 glass lid N, the joint being made tight with sealing wax. The leads are introduced 

 through holes drilled in the middle of the lid and the bottom of the pot. Over then 

 holes are placed the glass tubes p, q, up which the wires pass. These tubes have 

 flanges at the ends, ground flat so as to fit the flat surface to which they are 

 cemented. A side tube r provides the means of admitting and withdrawing gas. 

 The wires are fused through the tube at t and u. 



In order conveniently to vary the pressure and adjust it to any desired value, it 

 was necessary to provide a reservoir into which the gas could be drawn, or from 

 which it could be expelled, by raising or lowering a mercuiy vessel. It was also 

 necessary to provide a means of exhausting the apparatus. A special form of 

 mercury pump was designed, by means of which both these objects could be attained. 

 By thus dispensing with a separate reservoir, the apparatus was considerably 

 simplified. 



The pump is shown in fig. 2. The general arrangement of the various parts will, 

 it is hoped, be sufficiently clear from the figure, a is the pump, which also serves for 

 the adjustment of the pressure in the manner to be presently described, g is a 

 vacuum tube, which serves for observing the spectrum of the gas as a test of its 

 purity, /"and h are phosphoric anhydride drying tubes, d and c and p are ordinary 



3 c 2 



