VOLTAMETER (from roltaie. from H. Volta, name of the disenverer of the voltaic cell + metro)). measure). An instrument design ed to compare the intensities of electric currents by means of their ettects when passed through elec trolytes. (See ELECTRICITY.) It has been shown by Faraday and others that when an electric current is passed through an electrolyte the quantity of matter liberated at either of the electrodes—anode or cathode—varies directly as the quantity of current carried, that is, as the product of the intensity of the current and the time. Therefore, if different currents are passed through any one electrolyte, their intensities may he compared by noting the quantities (number of grams) of matter liberated in given intervals of time. It has been observed, however, that this law of Faraday is true only if the same speci fications are followed in the use of the apparatus for containing the electrolyte and obtaining the liberation of the matter. Such an apparatus is
called a `voltameter.' There are various forms of voltameters in use; one is so arranged as to collect any gases that may h, liberated at the electrodes, which in this ease are made of plati num, and the electrolyte is generally dilute sul phuric acid; another consists of a solution of copper sulphate in water, having two copper plates as electrodes; in another the electrolyte is a solution of silver nitrate in water contained in a platinum bowl which serves as the cathode, the anode being a disk of silver. (For the speci fications adopted by the National Academy of Sciences for the preparation and use of a silver voltameter, see A?tekaE.) There is an excellent resume of our present knowledge of the subject in a paper by Leduc in the Reports of the Inter national Congress of Physics, vol. ii., p. 440 (Paris, 1900).