What are Ions?

   lons is a term applied to the elements of an electrolyte, or a compound body undergoing the chemical process of electrolysis, as in silver-plating and other indus­trial uses. Those elements of an elec­trolyte which are evolved at the anode, or positive pole, are termed anions, and those which are evolved at the cathode, or negative pole, are called cations. When these are spoken of together, they are termed ions. Thus, .water when electrolyzed evolves two ions, oxygen and hydrogen, the former being an anion and the latter a cation. When the electric current is passed through water, bubbles of oxygen may be collected at one pole and bubbles of hydrogen at the other pole. Many scientists believe that free atoms of oxygen travel in one direction and free atoms of hydrogen in the opposite direction through the water. Hence, the term ion, which in Greek signifies a traveler, is applied to the atoms which travel to the two poles. The molecule of water consists of two atoms of hydrogen and one of oxygen, and the electric current splits up each molecule of water into the two groups of traveling atoms, going in different directions. The two kinds of ions, anions and cations, are believed to carry equal but opposite charges of electricity. The ion with a positive charge is attracted to the negative pole, and the ion with he negative charge of electricity to the positive pole. At the poles, or electrodes, each ion, whether an anion or a cation, is relieved of its elec­tric charge and resumes its chemical status as an ordinary atom of gas. Science has even measured the speeds of the traveling atoms during electrolysis, and it is said that the heaviest ions move faster than those of less atomic weight; due probably to the fact that the slower ions carry along with them some molecules of water, or whatever the solvent may be. In the pro­cess of silver-plating, and similar arts, the practical application of the theory of ions is seen. Thus a brass article, such as a fork, is dipped by a wire into a solution of silver cyanide in potassium cyanide, or some other silver salt. A small quantity of silver forms one of the electrodes or poles of the electric circuit—the anode. The fork is the other pole, or cathode. When an electric current is passed through the liquid bath, or electrolyte, positive ions of silver, or cations, are deposited on the brass fork, and it emerges from the electric bath as a silver-plated fork.