Excerpt from The Silver Coulometer
Specifications, as referred to above, were prepared by the National Academy of Sciences and legalized in the United States in 1894. They are practically in conformity with the earlier specifications of the British Board of Trade and read as ... follows: In employing the silver voltameter to measure currents of about one ampere the following arrangements shall be adopted: The cathode on which the silver is to be deposited shall take the form of a plati num bowl not less than 10 cm. In diameter and from 4 to 5 cm. In depth.
The anode shall be a disk or plate of pure silver some 30 sq. Cm. In area and 2 or 3 mm. 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 from 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.
The resistance of the voltameter changes somewhat as the current passes. To prevent these changes having 'too great an effect on the current, some resistance besides that of the voltameter should be inserted in the circuit. The total metallic resistance of the circuit should not be less than 10 ohms.
Method of making a measurement. - The platinum bowl is to be washed consecutively with nitric acid, distilled water, and absolute alcohol. It is then to be dried at 160° C. And left to cool in a desiccator. When thoroughly cool it is to be weighed carefully.
It is to be nearly filled with the solution and connected to the rest of the circuit by being placed on a clean insulated copper support to which a binding screw is attached.
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