The uses of the liquid acid are mainly in the production of chlorine, as a solvent for metals, and for medicinal and chemical purposes. Its properties are briefly as follows:-- It is a colourless or faintly-yellow acid liquid, the depth of colour depending on its purity, and especially its freedom from iron. The liquid is volatile, and can be separated from fixed matters and the less volatile acids by distillation; it has a strong attraction for water, and fumes when exposed to the air, from becoming saturated with aqueous vapour. If exposed to the vapour of ammonia, extremely dense clouds arise, due to the formation of the solid ammonium chloride. The acid, boiled with a small quantity of manganese binoxide, evolves chlorine. Dioxide of lead has a similar action; the chlorine may be detected by its bleaching action on a piece of paper dipped in indigo blue; a little zinc foil immersed in the acid disengages hydrogen. These two tests--viz., the production of chlorine by the one, and the production of hydrogen by the other--separate and reveal the constituent parts of the acid. Hydrochloric acid, in common with chlorides, gives a dense precipitate with silver nitrate. The precipitate is insoluble in nitric acid, but soluble in ammonia; it melts without decomposition. Exposed to the light, it becomes of a purple or blackish colour. Every 100 parts of silver chloride are equal to 25·43 of hydrochloric acid, HCl, and to 63·5 parts of the liquid acid of specific gravity 1·20. The properties of pure hydrochloric acid gas are as follows:--Specific gravity 1·262, consisting of equal volumes of hydrogen and chlorine, united without condensation. 100 cubic inches must therefore have a weight of 39·36 grains. The gas was liquefied by Faraday by means of a pressure of 40 atmospheres at 10°; it was colourless, and had a less refractive index than water. Water absorbs the gas with avidity, 100 volumes of water absorbing 48,000 volumes of the gas, and becoming 142 volumes. The solution has all the properties of strong hydrochloric acid, specific gravity 1·21. The dilute hydrochloric acid of the Pharmacopœia should have a specific gravity of 1·052, and be equivalent to 10·58 per cent. of HCl. §69. =Statistics of Poisoning by Hydrochloric Acid.=--The following tables give the deaths, with age and sex distribution, due to hydrochloric acid for ten years (1883-92):-- DEATHS FROM HYDROCHLORIC ACID IN ENGLAND AND WALES DURING THE TEN YEARS ENDING 1892. ACCIDENT OR NEGLIGENCE. Ages, Under 1-5 5-15 15-25 25-65 65 and Total 1 above Males, 1 16 2 ... 26 3 48 Females, ... 8 ... ... 9 1 18 ---------------------------------------------------- Totals, 1 24 2 ... 35 4 66 ----------------------------------------------------