ON THE SILVER VOLTAMK TKl:. 



551 



(5) The Syphon- Pot- Bowl Form (S.P.B.) (tig. 5). In this the liquids in the syphon 

 aud kathode vessel were separated by a porous pot. Any disadvantages of the 

 Richards form were thus introduced without eliminating any advantage of the 

 syphon. 



Fig. 5. 



Fig. 6. 



(6) The Elevated Kathode Form (fig. 6). A silver bowl with electrically deposited 

 silver formed the anode, and a platinum ring, or platinum bowl of smaller diameter 

 than that of the silver bowl, formed the kathode. If a heavy anode liquid was 

 formed, it would not come into such intimate contact with the kathode as in the 

 Rayleigh form. 



(7) Several Modifications of the above. (a) The silver anode in the Rayleigh type 

 was replaced by a platinum anode ; (b) for the filter paper of the Rayleigh form a 

 porous pot drilled with tine holes was substituted, and purified asbestos was placed in 

 the pot to prevent any anode slime reaching the kathode ; (c) in addition to the filter 

 paper a china filter cup with very fine holes surrounded the anode of the Rayleigh 

 form. The internal resistance was thus increased 100 times, and the potential 

 difference between anode and kathode was correspondingly increased. 



In all of the forms the platinum bowls used as kathodes were supported on brass 

 rings mounted on ebonite, and the silver rods supporting the anodes were clamped to 

 a metal arm projecting from a rod similarly mounted. From 300 to 400 cub. centims. 

 of solution were used in the large bowls and about 30 to 40 cub. centims. in the 

 small crucible loaned to us by Professor VAN DIJK. The solution was introduced by 

 means of a pipette and was similarly removed after the required amount of silver was 

 deposited. The liquid was carefully examined for loose silver, and if any was found, 

 the solution and the water used for washing the deposit were filtered through a hard 

 filter paper, the particles of the silver washed to the lowest part of the paper, and 

 the latter dried in an electric oven. By the aid of a pointed glass rod the loose 

 silver was transferred to the bowl. The main portion of the deposit was washed by 

 rinsing three or four times with distilled water, after which the bowl was filled with 

 water and left overnight. This last wash-water rarely showed more than the faintest 

 bluish colour on addition of neutral NaCl solution. Two more rinsings with water 

 followed, and then the bowl was dried by heating in an electric oven at 160 C. 



