149
1. Gaseous Hydrochloric Acid.
Preparation. —Hydrochloric acid, in the gaseous state, is procuredby the action of strong liquid sulphuric acid on dried chloride of sodium.The ingredients should be introduced into a tubulated retort, and thegas collected over mercury. Or they may be placed in a clean and dryoil flask, and the gas conveyed, by means of a glass tube curved twice atright angles, into a proper receptacle, from which the gas expels the airby its greater gravity.
In this process, one equivalent, or 60 parts of chloride of sodium, reacton one equivalent, or 49 parts of the protohydrate of sulphuric acid(strong oil of vitriol), and produce one equivalent, or 37 parts of hydro-chloric acid (gas), and one equivalent, or 72 parts of the sulphate ofsoda.
INGREDIENTS USED.
1 eq. Chlor dc . 5 1 eq. Chlorine.36
Sodium . 60 \ i eq. Sodium.
1 eq. LiquidSulph c . Acid49
PRODUCTS.
. 1 eq. Hydrochl c . Acid 37
leq.Soda32
lea. Suln te . Soda 72
Properties. —It is a colourless invisible gas, fuming in the air, in con-sequence of its affinity lor aqueous vapour. It is rapidly absorbed bywater. Its specific gravity is, according to Dr. Thomson, P2847. Ithas a pungent odour and acid taste. Under strong pressure (40 atmo-spheres) it becomes liquid. It is neither combustible nor a supporter ofcombustion. When added to a base (that is, a metallic oxide), waterand a chloride are the results.
Characteristics. —Hydrochloric acid gas is known by its fuming inthe air, by its odour, by its reddening moistened litmus paper, and byits forming white fumes with the vapour of ammonia, and by the actionof nitrate of silver on an aqueous solution of the gas, as will be men-tioned when describing the liquid acid.
Composition. —The composition of this gas is determined both byanalysis and synthesis. Thus, one volume of chlorine gas may be madeto combine with one volume of hydrogen gas, by the aid of light, heat,or electricity, and the resulting compound is two volumes of hydrochloricacid gas. Potassium or zinc heated in this acid gas, absorbs the chlorineand leaves a volume of hydrogen.
Constituents. Result. Eq. Eq.Wt. Per Cent. Vol. Sp. gr.
Chlorine .
i.
. 36 .
. 97-297
Chlorine gas . . 1 .
. 2-5
1 eq.Clilor.
= 36
1 eq.Hydro-chloric
Hydrogen
i.
. . 1 -
. 2-702
Hydrogen gas . 1 .
. 0-0694
1 eq.Hydr.
acid gas
= 37
Hydrochl c .Acid . .
!■-
. 37 .
. 10-000
Hydrochl c . Acid j ^gas.i *
. 1-2847
Physiological effects. — (a.) On vegetables. — Mixed with 20,000times its volume of atmospheric air, this gas is said by Drs. Christison and Turner (Christison ’s Treatise on Poisons) to have proved fatal toplants, shrivelling and killing all the leaves in twenty-four hours. But,according to Messrs. Rogerson ( Medical Gazette , vol. x. p. 312) itis not injurious to vegetables when mixed with 1500 times its volumeof air. Dr. Christison ascribes these different results to Messrs. Rogerson