ELCTROLYSIS. :\letal wires are not the only conductors for electric currents. although they are the Imes most emninonly seen. :Many liquids are conductors, and all gases may he made to conduct. To pass a current through a liquid or a gas, wires must. he used so as to conduct the current in at one point and out at another. The wire by which the current enters is called the 'anode'; that by \Odell it loaves, the 'cathode.' Fused metals eonduct like solid metals: hut in the ease of other liquid conductors (and also some solid ones) there are chemical actions at the anode and cathode: gases are evolved or solid matter is deposited on the metal wires or plates. Snell eonduetors are called 'cleetrolytes,' and the process of conduction through them is called 'electrolysis.' If all elellrolytes are examined it is found that they are the solutions of certain salts or acids in some liquid—such as water; and that there is evidence of the dissoeiation of the salt or acid by the action of the liquid. Fara day found by studying the relative quantities of flatter out from the liquid at the cathode and anode, when an electric current was through an electrolyte. two laws whieh bear His name: (1 I The mass of matter separated at either cathode or anode in any one electrolyte varies directly as the quantity of electricity ear rued by the current, i.e. as the product of the current-strength and the time. (2) if the same eurrent is passed through several electrolytes in series, the masses of the matter separated nut at the different anodes or cathodes vary directly as the 'chemical equivalents' of the matter.
The ehemieal equivalent of any element is its 'atomic weight' (see A-ro)Iie WEIR IITS ) vided by its 'valenee.' For example, the chemical equivalents of a few different substances are given in the following table: Hydrogen Oxygen 7.tit Clopper 31.59 3•2.4.1 saver Assuming the truth of Faraday's first law, a convenient method is offered fur comparing the current-strength of different currents, viz. pass the currents in turn through the same electrolyte and weigh the quantities liberated in the same time. The current-strengths are in the ratio of these masses. This is the principle of the so called silver or copper 'voltameters.' Faraday pictured the phenomena of electrolysis as being due to the passage in the electrolyte of two streams of partieles—onc set charged posi tively going toward the cathode, the other charged negatively going toward the anode. These carriers of charges lie called 'ions': and he thonght of them as giving up their charges to the cathode and anode, and then being liberated from the liquid, as gases or solid deposits. or as
then taking part in chemical reactions, and thus liberating other substances. ft is easily seen that, if Faraday's laws are exact. all ions of the same substance. e.g. hydrogen. must carry the same charge. in whatever electrolyte they appear; and further, that the charge on any ion is propor tional to its valence. (Thus. if the charge on a hydrogen ion is e, that on a copper ion must be •... because the valence of copper is twice that of hydrogen.)* The modern theory of electrolysis is one of the most important branches of physical chemistry. Only its essential ideas need be mentioned here. As it is known by evidence from many sides that an electrolyte consists of a pure liquid in which a salt or acid is dissolved and dissociated into parts, it is natural to identify the ions with these tra,mi•nts of the molecules of the salt or acid. The theory at present accepted is that by the net of solution in a liquid some substances are dissociated, at least in part: e.g. sulphurie avid in water: that is. some of the molecules of the dissolved substances break up into smaller parts. It is not thought that the parts of a molecule once dissocianI1 remain separated, but that there is a state of dissociation and recom bination going on as the molecules and their parts move about through the liquid, and at any in stant a definite proportion of molecules are dis sociated. It is natural to think that if a mole cule is broken into parts. which are then sepa rated. they will be electrically charged, one por tion positively. the other negatively. (The charges on any part would then vary as its va lence.) If a difrerence of potential is pro duc•d in the liquid by inserting the and cathode, all the positively charged parts will. during their intervals of dissociation, lie urged the cathode, while those charged will move toward the anode. (lt that these dissociated parts do not move freely by tltenlsehes. but drag with them definite masses of the solvent.) on this theory, which accounts perfectly for the observed phenomena of electrolysis, the ions are charged fragments of moletades. \\lien they get to the anode or cathode they give up their charges, and combine with other ions, thus forming molecules which are liberated. See Dissoci.vrtoN: ELECTRO CHEM ISTRY. 1 ;EN EIL\