152

ELEMENTS OF MATEIilA MEDICA.

College order the chloride to he heated to redness, to decompose anynitrate which which may be present; and, in order to insure the completedecomposition of the salt, employ a large excess of sulphuric acid, sothat the residual salt is the bisulphate of soda.

Properties. —Pure liquid hydrochloric acid is colourless, evolves acidfumes in the air, and possesses the usual characteristics of a strong acid.It has the odour and taste of the gaseous acid. Its specific gravityvaries with its strength. That of the London Pharmacopoeia is 1T6. Itis decomposed by some of the metals (as zinc and iron), hydrogen gasbeing evolved, while a chloride is formed in solution. It is decomposedby those oxyacids which contain five atoms of oxygen—namely, nitric,chloric, iodic, and bromic acids : the oxygen of these acids unites withthe hydrogen of the hydrochloric acid to form water. It combines withammonia, as well as with the vegetable alkalies, to form a class of saltscalled hydrochlorates or muriates. When it acts on a metallic oxide,water and a chloride are generated.

Characteristics. —A solution of nitrate of silver causes, withhydrochloric acid, a precipitate of the chloride of silver. This precipi-tate is known to be the chloride by its whiteness, its clotty or curdyappearance, its blackening by exposure to light, its insolubility in nitricacid, its solubility in ammonia, and by its fusibility (see p. 105). Whenpure, hydrochloric acid neither dissolves leaf gold, nor destroys the colourof sulphate of indigo. The addition of a few drops of nitric acid readilyenables it to dissolve gold. A rod dipped in a solution of causticammonia produces white fumes when brought near strong liquid hydro-chloric acid.

Composition. —At the temperature of 40° F. water absorbs 480 timesits bulk of hydrochloric acid gas, and forms a solution, having a specificgravity of 1-2109 (Sir H. Davy ’s Elements of Chemical Philosophy,p. 252). Prepared according to the London Pharmacopoeia, liquidhydrochloric acid has a sp. gr. of 1T6, and contains about a third of itsweight of hydrochloric acid gas.

Mr. E. Davy.Dr. Thomson.

Dr. Ure.

!

gr. 1T0 should saturate 132A better substance for ascer-Carrara marble (carbonate of

Sp. gr. of liquid acid. Hydrochloric acid gas Authority.

in 100 of liquid

1 16 . 32 32

1 162 33-945

1 1620 . 32-621

11641 33-029

1-1661. 33-437

1-1681 33-845

100 grains of liquid hydrochloric acid sp.grains of crystallized carbonate of soda,taining the strength of the acid is purelime): every 50 grains dissolved indicates 37 grains of real hydrochloricacid.

The Acidum hydrochloricum dilutum of the London Pharmacopoeia iscomposed of four fluid ounces of the strong liquid hydrochloric acid, andtwelve fluid ounces of water. One fluidrachm of it saturates very nearly32 grains of crystallized carbonate of soda (Phillips, Translation of thePharmacopoeia ).

Impurities. —The ordinary impurities of the common liquid hydro-chloric acid of the shops are perchloride of iron, sometimes a little freechlorine, and occasionally a little sulphuric acid. Dr. T. Thomson