Actinium in an Electric Field. 541 



through two bottles of concentrated sulphuric acid to dry it 

 and through a train of two or more tubes containing P 2 6 , 

 plugged at each end with glass wool, to absorb any residual 

 minute traces of moisture. The perfectly dry condition of the 

 last P 2 5 tube indicated that no trace of moisture was left in 

 the air current. This dry air current was then passed through 

 the tube containing the actinium preparation, which was 

 plugged at both ends with cotton wool. Finally the emana- 

 tion was led into the testing vessel through another cotton 

 wool plug. 



The vessel used in the experiments consisted of a brass 

 cylinder with an insulated central electrode sprung into a split 

 brass rod and very easily detachable from it. This rod in turn 

 was rigidly fixed in the tapered ebonite plug P, which fitted 

 closely into the guard-ring E. By employing sealing wax and 

 stop-cock grease all the joints, shown in the diagram, could be 

 made sufficiently air-tight. The dimensions of the vessel are 

 as follows : 



Inner height = 25-2 cms 



Inner diameter _ = 4 9 



Diameter of inlet = 3*8 



Diameter of central electrode . = -151 



Exposed length of central electrode .. = 23*1 



Distance of electrode from gauze = 1*8 



The diagram of connections is shown in fig. 1. H is a 

 spring-brass clip slipped over the brass rod to connect the cen- 

 tral electrode with the electrometer system. E is a guard tube, 

 which is always kept earthed to prevent any leakage over the 

 surface of the insulators. F is a brass ring which was employed 

 in order to remove the ebonite plug P and the electrode with- 

 out the necessity of handling the insulation. G is a piece of 

 fine-mesh gauze placed over the cotton wool in order to pre- 

 vent an abrupt change in the regularity of the electric field at 

 the bottom of the vessel and also to stop cotton wool particles 

 being blown into the test-vessel, b is a detachable brass piece 

 placed centrally over the gauze in order to make the flow sym- 

 metrical, as much as possible, with respect to the case and the 

 central electrode. The vessel was supported on the side by 

 spring-brass clips (not shown in the diagram) which were 

 mounted on ebonite and were connected to a series of high- 

 potential accumulators through the water resistance H and the 

 triple key M. 



The wire B in the figure goes to a second vessel, of con- 

 struction identical with A, except for the bottom, which was a 

 flat brass piece in this case. KR'D is a potentiometer arrange- 

 ment which was employed whenever it was necessary to charge 



