IONISATION

the di ociation of a molecule into electrically charged ions (g.v.). The phenomenon, according to the ionic hypothesis, can occur either in a gas or in the solutions of compounds. Before an electric current can pa through a gas or a solution, it is held that some ionisation must occur. In the case of a gas which is a poor conductor, ionisation may be brought about by pa ing X-rays through it, whereupon it become a good conductor. Similarly, a gas subjected to strong electrostatic discharge becomes ionised. An elaboration of the theory maintains that the ions of the gas travel with immense velocity and collide with neutral molecules. These molecules, by the force of the collision, are themselves broken up into ions, which in turn collide with other molecules. In this way, an enormous increase in the number of ions is brought about. The solutions of all salts are supposed to be more or le ionised, and when the two poles of a battery are dipped into a solution, the positively charged ions (metallic) travel to the negative pole, while the negatively charged ions (acidic) travel to the positive pole. As soon Bs the charged ions come in contact wit oppositely charged electrodes, they lose their charge and thereby become ordinary atoms, or groups of atoms as the case may be, with ordinary chemical activity. ‘The ionic hypothesis has been much attacked by some chemists of high standing, but while there are still many points connected with it which require explanation, it undoubtedly contains much truth and it serves a useful purpose until such time as the phenomena it seeks to explain can be further elucidated. (See also Di ociation.)