CHLORINE (Symbol Cl. Atomic, weight 35.5 ).—The elementary substances, chlorine, bro mine, iodine and fluorine, are called halogens, because they produce with other elementary sub stances bodies resembling almost in every respect the so-called oxysalts. Cyanogen, a compound radical, is often likened to the true halogens on account of it possessing properties similar to them.
Chlorine never occurs in a free state, but when combined with sodium it is found abun dantly in the earth, in solid and crystallized states in mines, dissolved in the sea water, in salt springs, in river water, and more or less in every organic being.
Chlorine gas is of a greenish-yellow color, of penetrable odor, irrespirable, causing inflam mation of the lungs, and finally death.
Water absorbs large quantities of the gas (2 volumes). The liquid known as chlorinated water has all the properties of the pure gas, and when standing for a length of time, deposits a yellowish crystalline precipitate—hydrate of chlorine.
For the preparation of chlorine gas the decomposition of hydrochloric acid by means of peroxide of manganese has been selected. The oxygen of the peroxide combines with the hydrogen of the hydrochloric acid, forming water, the manganese and chlorine form manga nese chloride and chlorine is set free. The other, and probably the most widely adopted method is to heat sea salt with peroxide of magnesium and sulphuric acid.
2NaC1 + + MnO, = 2C1 + + MnSO, + 2E1,0 Sodium Sulphuric Manganese Chlorine Sodium Manganese Water.
chloride acid peroxide sulphate sulphate Chlorine is not combustible, and one of its most remarkable properties is its power to com bine with hydrogen to form hydrochloric acid. This acid is a colorless gas, is soluble in water, and one volume of it absorbing 454 volumes of the gas. This is the crude hydrochloric or muriatic acid, containing iron, arsenic and sulphuric acid. Rectification produces a chemically pure article, as used by analysts and photographers.
A mixture of hydrochloric acid with nitric acid is termed aqua regia, because gold can be dissolved with it. Its solvent action depends upon the fact of containing free chlorine, liberated
by the action of oxygen upon the nitric acid. The metal combines directly with this free chlorine, and soluble chlorides are formed.
Chlorine combines, but indirectly, with oxygen, giving rise to the following oxyacids of chlorine : Hypochlorous acid, or hydrogen hypochlorite, HC10. Chlorous acid, or hydrogen chlorite, Chloric acid, or hydrogen chlorate, HC10,. Perchloric acid, or hydrogen perchlorate, Hypochlorous acid finds employment in photography as a bleaching agent and a powerful hyposulphite of sodium eliminator. The combinations with sodium, potassium and zinc are well known and appreciated. Chlorine peroxide and chlorous acid have not entered into photographic practice, but chloric acid or hydrogen chlorate is, in the form of potassium chlorate, very much used as an ingredient in various flash-light compounds, on account of its explosive properties.
When potassium chloride is heated to fusion a new salt, potassium perchlorate, is formed, Perchloric acid and its salts are extremely powerful oxidizers, and have for that reason been recommended as ingredients for flash-light powders. But their force of explosion is so very violent that their employment has been but very limited and has finally been totally abandoned.
Of chlorine combinations highly interesting to the photographer and useful to him in a variety of ways are terchloride of gold, chloride of gold, and sodium or potassium, chloride of silver, ammonium or potassium or sodium chloride, chloride of calcium or chloride of lime, a mechanical mixture of hypochlorite of lime and calcium chloride. Ferric chloride plays an impor tant part in many of the lichtdruck processes, and is sometimes used as an intensifier, at other times as a reducer. Chloride of copper has been recommended as a reducer, and there are many others of more or less importance to the student.