MURIATIC ACID, or HYDRO cutoma ACID. This acid was originally discovered by Glauber, and called by him spirit of salt. In its pure or gaseous form it was first obtained by Priestley in 1744; and its true composition was shown by Davy in 1809, who proved it to be a com pound of hydrogen and chlorine ; hence it has been termed hydrochloric apiel. Muriatic acid gas is procured by acting upon common salt (which is a chloride of sodium) by concentrated sulphuric: acid. The water of the acid is decom posed, and its hydrogen combines with the chlorine of the salt to form muriatic acid ; while the oxygen is transferred to the sodium, which is thus converted into soda, and this unites to the sulphuric acid to form sulphate of soda. 60 parts of common salt, and 49 parts of concen trated sulphuric acid, afford, by this mutual action, 87 parts of muriatic acid, and 72 of sulphate of soda. Muriatic acid gas may also be formed by passing an electric spark through a mixture of equal volumes of chlorine and hydrogen ; or by exposing such mixture to the sun's rays, or inflaming them by a taper, they burn with explosion, and form a volume of mnriatie acid equal to the united vol umes of the gases. As the specific gra vity of hydrogen is to that of chlorine as 1 to 86, the specific gravity of the result ing muriatic acid gas compared with hy drogen will be 18.5, and 100 cubic inches of it will weigh 89.8 grains. Muriatic acid gas is rendered liquid under a pressure of 40 atmospheres of the temperature of ; it extinguishes flame, and is intense ly sour, powerfully reddening vegetable blues. Water absorbs it with much vio lence, taking up about 480 times its vol ume. This is the state in which muriatic acid is generally used. Its specific gravity is about 1.19, and it is commonly obtain ed by distilling a mixture of equal weights of salt, sulphuric acid, and water. When muriatic acid acts upon metallic oxides, it generally happens that a mutual de composition of the oxide and acid ensues; the oxygen of the oxide unites to the hydrogen of the acid to form water, and the metal to the chlorine to form a metal lic chloride. Thus it is that soda and
muriatic acid form a chloride of sodium or common salt. The most effective test of the presence of muriatic acid is nitrate of silver, which forms an insoluble chloride of silver in all solutions containing muri atic acid or muriates.
The muriatic acid of commerce has usually a yellowish tinge, but when chemically pure it is colorless. It fumes strongly in the air, emitting a corrosive vapor of a peculiar smell. The straw color is due to the presence of chloride of iron, obtained from the vessel in which it was made. It may be freed from this by distillation.
The preparation of this acid upon a great scale is frequently effected in this country by acting upon sea-salt in hem ispherical iron pots, or in cast-iron cy linders, with concentrated sulphuric acid ; taking 6 parts of the salt to 5 of the acid. The mouth of the pot may be covered with a slab of silicious freestone, perfo rated with two holes of about two inches diameter each, into the one of which the acid is poured by a funnel in successive portions, and into the other, a bent glass, or stone-ware tube, is fixed, for couduct ing the disengaged muriatic gas into a series of large globes of bottle glass, one third filled with water, and laid on a slop ing sand-bed. A week is commonly em ployed for working off each pot; no heat being applied to it till the second day.
Liquid muriatic acid has a very smr corrosive taste, a pungent suffocating smell, and acts very powerfully upon a vast number of mineral, vegetable, and animal substances. It is much employed for making many metallic solutions and in combination with nitric acid, it forms the aqua regia of the alchemists, so called from its property of dissolving gold.