HYDROCHLORIC 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 Priest ley in 1 774; and its true composition was shown by Davy in 1809, who proved it to be a compound of hydrogen and chlorine; hence it has been termed hydrochloric acid. 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 decomposed, and its hydrogen combines with the chlorine of the salt to form muriatic acid; whilst 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 concentrated sulphuric acid, afford, by this mutual action, 37 parts of muriatic acid, and 72 of sulphate of soda. Muriatic acid gas may also be formed by pa ing 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 muriatic acid equal to the united volumes of the gases. As the specific gravity of hydrogen is to that of chlorine as 1 to 36, the specific gravity of the resulting muriatic acid gas compared with hydrogen will be 18-5, and 100 cubic inches of it will weigh 393 grains. Muriatic acid gas is rendered liquid under a pre ure of 40 atmospheres of the temperature of 50°; it extinguishes flame, and is intensely sour, powerfully reddening vege-. table blues. Water absorbs it with much violence, taking up about 480 times its volume. This is the state in which muriatic acid is generally used. Its specific gravity is about I'l9, and it is commonly obtained 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 decomposition of the oxide and acid ensues; the oxygen of the oxide unites to the hydrogen of the acid to lorm water, and the metal to the chlorine to form a metallic 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 [s. 793]