I'ONIZA'TION (from ion, from Gk. pre-. part. of itrai, icn1i, to go). The modern theory of electric conduction is that an electric current consists of the motion of minute particles of matter which are charged positively and nega tively, the motion of the oppositely charged par ticles being in opposite directions. These charged particles are called 'ions.' and they are in no case identical with molecules: in fact. there is no evidence of a molecule as sueh being charged. The formation of these ions is called ionization. In metals and all solid conductors there are ions probably always present, but in what state it is not known. In a liquid ions are produced by dissolving in it sonic salt or acid, which `dissociates' in the act of solution (q.v.). In ordinary gases ions are probably always present to a limited extent, although in a pure dry gas there may be none: but in any case their number may be enormously increased in many ways. If the Rontgen or X rays (q.v.) are passed through a gas, it is ionized, as is shown by its becoming a good conductor; similarly, if uranium rays (q.v:) or rays from any radio-active substance, or ultra-violet light, or the cathode rays pass through a gas, it is ionized. If the temperature of certain gases is raised, they hecome con ductors: or if a spark is passed between two balls joined to an electrical machine or induction coil. the gas on all sides becomes a conductor; if there is a 'brush discharge' off points, the same is true. ,Many gases when formed by elec trolysis in liquids are found to be ionized.
The whole subject of ionization is still under investigation; but several facts seem to be now assured: (1) The ions are not molecules.
(2) The negatively charged ions have less mass than the positively charged ones. and move
more rapidly under the action of a given electric force.
(3) The ionization of any one gas. however produced. gives the same result; e.g. the ions of oxygen gas are always the same.
(4) The negatively charged ions of all gases are identical.
it seems probable. but not certain, that the charge carried on an ion of any substance in the gaseous state is the same as that carried on an ion of the same substance in a liquid. e.g. a hydrogen ion in hydrogen gas. and a hydrogen ion produced by dissolving sulphuric acid in water. The masses of the ions in the two cases are quite different, the gaseous one being about one-thousandth as heavy as the other. (It mar be that in the ease of the liquid-electrolyte the ion drags with it a quantity of uncharged mat ter.) According to the latest experiments of J. J. Thomson. the mass of a negatively charged ion is of the order grams: the ratio of this mass to the charge carried is about the charge carried by each ion being about 6.5 X electrostatic units.
It requires energy to ionize a gas, and some experiments of Rutherford give as an approxi mate value of the number of ergs necessary to ionize a gas 1.0 X ergs per ion. Similarly in the ionization of a salt or acid by going into solution, there are energy changes. It has been estimated that the amount of energy required to ionize 6:t grams of copper in a liquid electrolyte is approximately 17,700 calories or 7 t,310 joules; while, when 05 grains of zinc are ionized, 33,100 calories, or 139,000 joules, are liberated. (03 grains of copper and 0:i grains of zinc are 'equiv alent' amount s. )