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.

The SI unit for quantity of electricity is the coulomb, while the SI unit for electric potential is the volt.

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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.

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.

Copper voltameter

This is similar to the silver voltameter but the anode and cathode are copper and the solution is copper sulphate, acidified with sulphuric acid. It is cheaper than the silver voltameter, but slightly less accurate.

Sulphuric acid voltameter

The anode and cathode are platinum and the solution is dilute sulphuric 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.

Electrochemical equivalents

The electrochemical equivalent of an element is the mass of that element (in grams) transported by 1 coulomb of electricity.

Sources

• Practical Electricity by W. E. Ayrton and T. Mather, published by Cassell and Company, London, 1911, pp 12-26