CLARK CELL AS A STANDARD OP ELECTROMOTIVE FORCE. 
571 
II. A bowl, kindly lent us by Professor Liveing, 10 cms. in diameter, 3'5 cms. in 
depth, the bottom of this is flatter than that of I., and the sides more nearly vertical. 
III. A bowl, very similar to I., and of about the same dimensions, also lent us by 
Professor Liveing. 
IV. A third bowl, similar to I., and of about the same size, though much lighter, 
lent us by Mr. F. H. Neville. 
V. A deep cup-shape bowl, 7'25 cms. in diameter, 8 cms. deep, belonging to the 
Laboratory. 
Of these, No. II. had been used a good deal for chemical work. Its surface was 
somewhat dull, and we never succeeded in obtaining an adhesive deposit with it. Traces 
of the silver always came away in the washing, and when weighed, the silver was 
always less than that deposited in the other bowl. We have not used the deposits 
from this bowl. 
In each experiment two bowls were used in series. 
The anode was usually a circular piece of silver plate, about 7 or 8 cms. in diameter, 
and '12 cm. in thickness, supplied by Messrs. Johnson and Matthey as “Ordinary 
Fine Silver Sheet,” price 5s. per oz. This was supported horizontally in the liquid by 
three platinum wires, the w hole being covered with filter paper secured at the back 
with sealing wax. 
In the case of Bowl V., the anode was bent into the form of a cylinder, which was 
immersed in the liquid with its axis vertical. 
The bowls rested on clean copper plates insulated on ebonite and paraffin blocks. 
The supports which carried the anodes were insulated in the same way. The insula¬ 
tion was tested by connecting up the voltameters before they had been filled with the 
liquid with a battery of six Leclanche cells and a delicate high-resistance galvano¬ 
meter. No trace of a leak could be found. 
The liquid used was a solution of silver nitrate, containing 85 parts by weight of 
distilled water and 15 parts of pure recrystallised silver nitrate, supplied by Messrs. 
Johnson and Sons, as containing 63'5 per cent, of fine silver, or 99-f per cent, of pure 
anhydrous nitrate of silver. 
A coil of wire, having about the same resistance as two of the voltameters, was 
connected up in parallel with them, in such a way that, by means of a key consisting 
of mercury cups cut in a block of paraffin, the current could be sent either through the 
voltameters or through the coil. The adjustments were made with the current 
flowing through the wire, when all w r as complete the key was shifted so as to send the 
current through the voltameters, and the time taken. 
§ 5. The Standard Resistance. 
It was necessary that this should not be seriously heated by a current of about 
1 ampere. 
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