Voltameter
A Voltameter is a scientific instrument used for measuring quantity of electricity. It should not be confused with a voltmeter which measures electric potential. An alternative name is coulometer.
The SI unit for quantity of electricity is the coulomb, while the SI unit for electric potential is the volt.
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[edit] Types of voltameter
The voltameter is an electrolytic cell and the measurement is made by weighing the element deposited or released at the cathode in a specified time.
[edit] Silver voltameter
This is the most accurate type. It consists of two silver plates in a solution of silver nitrate. When current is flowing, silver dissolves at the anode and is deposited at the cathode. The cathode is weighed, current is passed for a measured time, then the cathode is weighed again and again.
[edit] Copper voltameter
This is similar to the silver voltameter but the anode and cathode are copper and the solution is copper sulfate, acidified with sulfuric acid. It is cheaper than the silver voltameter, but slightly less accurate.
[edit] Mercury voltameter
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[edit] Sulfuric acid voltameter
The anode and cathode are platinum and the solution is dilute sulfuric acid. Hydrogen is released at the cathode and collected in a graduated tube so that its volume can be measured. The volume is adjusted to standard temperature and pressure and the mass of hydrogen is calculated from the volume. This kind of voltameter is sometimes called Hofmann voltameter.
[edit] Electrochemical equivalents
The electrochemical equivalent of an element is the mass of that element (in grams) transported by 1 coulomb of electricity.
| Element | Electrochemical equivalent |
|---|---|
| Silver | 0.0011181 |
| Copper | 0.0003281 |
| Hydrogen | 0.0000104 |
[edit] Historical derivation of the name
Faraday used an apparatus that he termed a "volta-electrometer", subsequently Daniell called this a "voltameter".[1]
[edit] See also
[edit] Sources
- Practical Electricity by W. E. Ayrton and T. Mather, published by Cassell and Company, London, 1911, pp 12–26
[edit] References
- ^ Frank A. J. L. James, (1991), The correspondence of Michael Faraday, IET, ISBN 0863412491, letter 872, 9/1/1836
