64 Dr. H. J. S. Sand on the Concentration 



of the electrode would suddenly within about half a minute 

 become uniformly covered with tiny bubbles of hydrogen. 

 The current was at the same time observed, the measuring' 

 instrument, as described later on, being either a Weston 

 milli voltmeter or an Ayr ton- Mather D'Arsonval galvano- 

 meter. When employing the former, the current seemed to 

 remain absolutely constant till shortly before the hydrogen 

 bubbles were visible, when suddenly a considerable drop 

 would take place. In the actual quantitative experiments in 

 which the Weston instrument was employed, the time which 

 passed from the beginning of the experiments till this drop 

 of the current occurred was taken as the time which elapsed 

 until the hydrogen came off. 



When employing the W Arson val, however, it was seen 

 that the current at first kept slowly decreasing, until it would 

 after a certain time drop considerably and then become 

 fairly constant again. It was seen that after the drop had 

 taken place, the hydrogen bubbles always began to appear. 

 In the experiments in which the B'Arsonval was employed, 

 the time when the sudden drop was completed was taken as 

 that when hydrogen bubbles first appeared. In these 

 experiments a Thomson-Varley rheostat was always intro- 

 duced into the circuit, by regulating which the current was 

 kept perfectly constant until the large drop occurred. The 

 behaviour of the Weston instrument was probably due to a 

 slight sticking effect. 



Three types of apparatus were employed, which will be 

 understood from the accompanying figures 1-3. Tubes of 

 the first type were employed for experimenting on solution A. 

 The cathode consisted of an engravers'' plate. It was fixed to 

 the end of the tube, which was ground perfectly flat, by 

 Chatterton cement. As it allowed a spirit-level to be placed on 

 its top, the apparatus could be adjusted so as to make the 

 cathode perfectly horizontal. The anode in this apparatus 

 consisted of copper gauze. As seen from the figure, the tube 

 was closed by a rubber stopper, into which a groove g was cut 

 to allow air-bubbles to be easily removed. The rubber 

 tube r was filled by introducing a long thin glass tube into 

 it, down which the solution was poured by means of a funnel. 

 In Ihe first few experiments tabulated, the original surface 

 of the plate was employed. In the later experiments it was 

 amalgamated in order to secure as uniform a deposit as 

 possible. Apparatus of this type, of which several were 

 made, showed the disadvantage, that the plate forming the 

 cathode occasionally came off, besides it could not be readily 

 removed for examination and cleaning purposes. 



