CHLORIN ETRY, or CHLOROM'ETRY, is the process of estimating the proportion of available chlorine in bleaching powder (q. v.), which may vary from 20 to 36 per cent. The process depends upon the great power with which chlorine, in the act of being liberated from its compounds, causes the oxidation of many substances. The salt gen erally used is pure crystallized sulphate of iron, which, in its ordinary state, gives a deep blue color, with a drop of ferridcyanide of potassium, but ceases to do so when it has been fully oxidized, or converted from a proto-salt into a per-salt, through the influence of chlorine. It being known that 78 grains or parts of sulphate of iron are oxidized by 10 grains or parts of chlorine, the mode of procedure in C. is as follows: 78 grains of fine crystals of the sulphate of iron are dissolved in water slightly acidulated with hydrochloric acid in a white porcelain basin. A. given quantity of the bleaching powdersay 50 grainsis dissolved in a little tepid water, and introduced into a tall measure-glass called a chlorimeter or burette, similar to an alkalimeter, which is divided into 100 parts, and water added till the solution rises to the top mark. After subsidence
of the insoluble matter, the clear solution is very gradually poured into the solution of sulphate of iron in the basin, the whole being kept constantly stirred, and every now and again a drop of the iron solution is taken out and placed on a new drop of ferrid cyanide of potassium placed on a white plate; and whenever the iron solution ceases to produce a deep blue, and only forms a light greenish-yellow tint, it is known that the iron has been fully oxidized by the chlorine. Suppose that at this stage the burette has been emptied to the 55th division; as we know that the liquid poured out must have contained 10 grains of chlorine, we can calculate the chlorine contained in the whole; for Thus 50 grains of the powder contain 18.18 grains of chlorine, or 36.36 per cent. Protocbloride of manganese, subchloride of mercury (calomel), or a solution of indigo of known strength, may be employed instead of the sulphate of iron; but the latter is preferable, and is generally employed by chemists and manufacturers.