Free chlorine occurs in the form of a greenish-coloured gas, having a peculiar acrid odour, very soluble in water, especially when cold; it possesses intense chemical powers, bleaches all vegetable colours, and acts as a powerful disinfectant, probably by decomposing the organic particles producing diseases. For this purpose it can be evolved from chlorated lime by the addition of some acid, or more economically by the following method:- Mix one part of common salt and one part of bin-oxide of manganese intimately together, and add to these (put into a shallow dish) two parts by weight of oil of vitriol previously diluted with two parts of water; such a mixture will continue to give off chlorine for some days.
Prep. (Hydrochloric acid, six fluid ounces; black oxide of manganese, in fine powder, one ounce; distilled water, thirty-four fluid ounces. Mix the acid and oxide in a retort, then pass the chlorine through an intermediate small phial, containing three ounces of water, to the bottom of a three pint bottle containing the remainder of the water, until it has almost ceased to be given off.) In this process the decompositions which take place are represented in the formula (2 H Cl + Mn O2=Mn Cl + 2 HO + C1).
Prop. & Comp. This is a solution of chlorine gas dissolved in half its volume of water, and constituting 0.006 of the weight of the solution. It is a liquid, having a slight green colour, with a very strong odour of chlorine, and immediately discharging the colour of a dilute solution of sulphate of indigo; when exposed to the light it is decomposed, with the formation of hydrochloric acid and oxygen, and hence should be used recently prepared.
Therapeutics. Its action as a remedy resembles that of the Liquor Sodas Chloratae, and it may be used, when diluted about seven times with water, as a gargle or lotion; or, still more dilute, it may be given as an internal remedy in low or typhoid states of the system, as malignant scarlatina, etc.
Tests. Sp. gr. 1.003, leaves no residue on evaporation. When 20 grains of iodide of potassium, dissolved in an ounce of distilled water, are added to a fluid ounce of this preparation, the mixed solution acquires a deep red colour (from the liberation of iodine), which requires for its discharge 75 measures of the volumetric solution of hyposulphite of soda, equivalent to 2.67 grains of chlorine.
Dose. 10 min. to 30 min. freely diluted.