<P> These oxidation / reduction processes have 100% efficiency with the wide range of the current densities . Measuring of the quantity of electricity (coulombs) is based on the changes of the mass of the mercury electrode . Mass of the electrode can be increased during cathodic deposition of the mercury ions or decreased during the anodic dissolution of the metal . </P> <P> 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 . </P> <P> Faraday used an apparatus that he termed a "volta - electrometer"; subsequently Daniell called this a "voltameter". </P> <P> A coulometer is a device to determine electric charges . The term comes from the unit of charge, the coulomb . There can be two goals in measuring charge: </P>

What is the difference between voltmeter and voltameter