- Weight voltameters;
- Gas voltameters.
Ques. What is the difference between these two classes of voltameter?
Ans. In one, the current strength is determined by the weight of metal deposited or weight of water decomposed, and in the other by the volume of gas liberated.
[Fig. 544] shows a weight voltameter and [fig. 545] a gas voltameter.
Ques. How should the plates of a weight voltameter be treated before use?
Ans. They must be thoroughly cleaned and polished with sandpaper, the sand being afterwards removed by placing them in running water. The fingers must not be placed on any part of the plate which is to receive the deposit.
Ques. What form of voltameter has been selected to measure the International ampere?
Ans. The silver voltameter arranged as here specified:
The cathode on which the silver is to be deposited shall take the form of a platinum bowl, not less than 10 cms. in diameter, and from 4 to 5 cms. in depth.
The anode shall be a disc or plate of pure silver some 30 sq. cms. in area, and 2 or 3 cms. in thickness. This shall be supported horizontally in the liquid near the top of the solution by a silver rod riveted through its center.
To prevent the disintegrated silver which is formed on the anode falling upon the cathode, the anode shall be wrapped around with pure filter paper, secured at the back by suitable folding.
The liquid shall consist of a neutral solution of pure silver nitrate containing about 15 parts by weight of the nitrate to 85 parts of water.
Ques. What is the value of the International ampere as measured with the silver voltameter?