Muriatic acid, hydrochloric acid, has but a limited use. Its chemical sign is Hc1, appears in commerce from 18 to 22 degrees (Bme.), specific gravity 1.15 to 1.17, containing about 30 to 33 per cent, of anhydrid acid, and displaces from 18 to 20 per cent. of its weight of carbonic acid from carbonates and double the quantity from bi-carbonates. Enormous quantities of hydrochloric acid are produced in the preparation of potash and of carbonate of sodium. The soda factories abound with it. The crude hydrochloric acid is of a yellowish color and usually contains traces of sulphuric and sulphurous acids, aluminium and iron. It should be free from arsenic, which may be detected, according to Bettendorf, by adding 1 gm. of stamous chloride to 10 gm. of the acid, and either heating or setting aside for half an hour, when a brown turbidity or precipitate will occur, consisting of metallic arsenic. One-millionth part of arsenic may thus be detected, provided the acid has not been diluted. After the precipitate has settled, the clear liquid may be carefully decanted or filtered, and afterward distilled, when it will be free from arsenic and tin.

To test it for sulphurous acid or arsenic, the United States Dispensatory gives the following directions: Put a few picees of pure zinc into a rather long test-tube, and introduce the hydrochloric acid, diluted with 2 parts of water, which should fill about one-tenth part of the tube. In the upper part of the tube place a small bunch of cotton moistened with solution of acetate of lead, and cover the mouth of the tube with a piece of white filtering-paper moistened with solution of nitrate of silver. After the evolution of hydrogen gas has continued for half an hour, neither the cotton nor the paper should be blackened, proving the absence of sulphurous acid in the former case, and of arsenic in the latter. Under the conditions described, sulphurous acid evolves sulphuretted hydrogen, which blackens the lead salt, and arsenic yields arseniuretted hydrogen, which does not affect lead acetate, but blackens nitrate of silver.

Purified hydrochloric acid is a colorless liquid of 1.160 sp. gr. and emitting white vapors in contact with the air. It gives with nitrate of silver a white curdy precipitate, which is soluble in ammonia and insoluble in nitric acid. Muriatic acid can be used for all kinds of carbonates, but requires, like sulphuric acid, for the decomposition of dolomite, some heat; but all the carbonates should be in small fragments, not powdered, to guard against a sudden ebullition of gas, which would occur when powdered carbonates would be used, causing excessive foaming and choking up the pipes. Crude muriatic acid should never, and the purified acid only be used, when particular circumstances commend or local considerations recommend it, and then only when diluted to about 20° Brae. The corrosive vapors of the concentrated acid, which escape when opening a carboy, would disadvantageously fill the working-rooms. Sulphuric acid liberates at a smaller volume the greatest quantity of carbonic acid gas; its use is therefore preferable, besides its price being cheaper. The quantity of muriatic acid required occupies at 20 degrees Bme. about three and one-fourth, at 15 degrees nearly five and a half times the volume of the required sulphuric acid.

The acid chambers on ordinary apparatus do not stand this capacity. Therefore when muriatic acid is substituted for sulphuric in ordinary apparatus, a smaller amount of carbonate has to be used to correspond with the capacity of the acid chamber, and in order to do a certain amount of carbonating, the operation has to be repeated as often as necessary. But besides this inconvenience there are other disadvantages connected with the use of muriatic acid. It very easily happens, especially when attention on the part of the operator is lacking, that gas is too quickly generated and chlorine gas escapes, and passes the purifiers or washers with the carbonic acid gas unabsorbed, entering the fountains and spoiling the beverage.

Even if purified, the muriatic acid has not unfrequently a disagreeable, urinous smell, which is difficult completely to remove. Wherever muriatic acid is in use or likely to be tried, this will call the attention of the manufacturer to its characteristics, and caution him in its use.