Cooley's Cyclopaedia of Practical Receipts Volume I Part 279

Golden seal has been given in the form of infusion, decoction, tincture, and extract, and the fluid extract is now officinal in the United States'

Pharmacopia.

=HY'DRATES.= Compounds of hydroxyl (HO) with other bodies, _e.g._ KHO--hydrate of pota.s.sium. The term hydrate is also given to chemical combinations of water (H_{2}O) with other substances, _e.g._ C_{2}HCl_{3}O.H_{2}O--hydrate of chloral.

=HY'DRIDE.= A compound of hydrogen with another radical, _e.g._ hydride of methyl--CH_{3}H.

=HYDRIO'DATE.= A name formerly given to the salts now termed iodides. See IODIDES.

=HYDRIO'DIC ACID.= _Syn._ IODHYDRIC ACID; ACIDUM HYDRIODIc.u.m, L. An acid compound of iodine and hydrogen. See IODINE.

_Prep._ 1. By heating iodine in hydrogen, the volume of the gas becomes doubled, and a colourless acid gas is produced; it is, however, never prepared for use by this means. 2. Place 10 parts of pota.s.sic iodide in a small retort with 5 parts of water, and add 20 of iodide; then drop in cautiously one part of phosphorus, cut into small fragments, and apply a gentle heat. The gas will be given off abundantly and may be collected, by displacement, in dry bottles.

A solution of hydriodic acid may be prepared by suspending iodine in water, and pa.s.sing a current of sulphuretted hydrogen through the mixture until the brown colour of the iodine disappears; sulphur is deposited in abundance, and hydriodic acid formed.

=HYDRO'BENZANIDE.= White crystalline ma.s.s, obtained from oil of bitter almonds by treatment with ammonia.

=HYDROBRO'MIC ACID.= See BROMIDE.

=Hydrobromic Acid.= (HBr.) _Syn._ HYDRIC BROMIDE, HYDROGEN BROMIDE.

_Prep._ This very powerfully acid gaseous body may be prepared as follows:--1. By decomposing bromide of pota.s.sium with a concentrated solution of phosphoric acid. 2. By decomposing bromide of phosphorus by means of a small quant.i.ty of water.

Hydrobromic acid gas is colourless and non-inflammable; it extinguishes flame. It is extremely irritating to the lungs when breathed. It is very soluble in water.

=HYDROBRO'MIDE.= _Syn._ BROMIDE (which _see_).

=HYDROCAR'BON.= A compound of carbon and hydrogen. The hydrocarbons const.i.tute a most important series of organic compounds.

=HYDROCHLORIC ACID.= (HCl = 365.) _Syn._ MURIATIC ACID, HYDRIC CHLORIDE, HYDROGEN CHLORIDE. This important gaseous compound was discovered by Priestly in 1772. In nature it is given off with other gases from active volcanoes, and is occasionally to be met with in the springs and rivers of volcanic districts. When hydrogen and chlorine are mixed in equal volumes, they are without action upon each other if kept in the dark, but if exposed to direct sunlight, chemical combination, accompanied by a loud explosion, instantly takes place between them, the result of their union being the colourless gaseous, intensely sour hydrochloric acid. If, instead of bright suns.h.i.+ne, the mixed gases are exposed to diffused daylight, chemical union also ensues between them, but the process is then a slow and gradual one; the pa.s.sage through them, however, of the electric spark, or the application of a lighted match or taper instantly causes their explosion and combination.

One volume of chlorine unites with one volume of hydrogen, forming two volumes of hydrochloric acid; no condensation occurs in the act of union.

Hydrochloric acid may also be formed by transmitting moist chlorine through a red-hot porcelain tube; oxygen being at the same time liberated.

_Prep._ Hydrochloric acid, save for the purposes of ill.u.s.trative experiment, is never obtained by any of the above processes. An easy mode of procuring it, when required for laboratory use, is to heat the ordinary aqueous solution of the acid in a flask, and to collect the gas, which is given off by displacement. It may also be readily got by introducing pieces of common salt (which should have been previously fused in a crucible at a red-heat and allowed to cool) into a gla.s.s retort, and pouring over them about twice their weight of oil of vitriol. The hydrochloric acid, which escapes very abundantly, must be collected either by displacement or over mercury.

_Prop._ Hydrochloric acid is a colourless gas, very acid to the taste, and irritating to the eyes; and induces coughing even if breathed in small quant.i.ties, or when largely diluted. It is very destructive to vegetation, on which account the soda manufacturer is compelled by law to condense and thus prevent the escape of its fumes. It has a specific gravity of 1261.

When subjected to a pressure of 40 atmospheres at 50 F., it becomes a colourless fluid capable of dissolving bitumen, and having a specific gravity of 127. It has never been frozen. Hydrochloric acid neither burns, nor supports combustion. The white fumes which it forms when exposed to the air, are due to its condensing the atmospheric moisture, and thus giving rise to a body less volatile than water. This gas is greedily and instantly absorbed by water. A fragment of ice placed in a jar of the gas absorbs it, and becomes immediately dissolved.

=Hydrochloric Acid, Solution of.= The hydrochloric acid of commerce is a solution of the above gas in water. When exposed to the air it emits grey fumes. Water at 40 F. absorbs about 480 times its bulk of hydrochloric acid, increasing in volume about one third in doing so, acquiring a density of 12109, and then containing nearly forty-three per cent. of the acid.

_Strength of Solution of Hydrochloric Acid, 77 Fahr._ (E. DAVY.)

--------------------------------------------------- Hydrochloric Hydrochloric Sp. Gravity. acid in Sp. Gravity. acid in 100 parts. 100 parts.

------------------------- ------------------------- 121 4243 110 2020 120 4040 109 1818 119 3838 108 1616 118 3636 107 1414 117 3434 106 1212 116 3232 105 1010 115 3030 104 808 114 2828 103 606 113 2626 102 404 112 2424 101 202 111 2222 ---------------------------------------------------

In the laboratory, solution of hydrochloric acid is in constant use. It may be easily prepared from chloride of sodium and sulphuric acid. The retort should be connected with a couple of Woulfe's bottles; into the first of which a small quant.i.ty of water should be poured, to detain any impurities mechanically carried over with the gas; the second bottle should contain four parts of water, and should be placed in a vessel of cold water, as the gas in becoming condensed, disengages a large amount of heat. The gas comes off and is absorbed readily by the water upon applying a gentle heat to the retort.

It is by this last method that solution of hydrochloric acid is obtained in such enormous quant.i.ties[347] for the various purposes in which it is used, in the arts and manufactures.

[Footnote 347: In South Lancas.h.i.+re alone, more than 1000 tons of hydrochloric acid in solution are made weekly.]

Hydrochloric acid is, in fact, a by-product in the manufacture of carbonate of soda, and is generated during the first stage of the operation, known as the salt-cake process, which consists in the decomposition of salt by sulphuric acid, and is accomplished in a furnace called the salt-cake furnace.

The hydrochloric acid gas which is given off escapes from the furnace through a flue with the products of combustion into high brick towers filled with c.o.ke or stones, over which a stream of water trickles down, the whole of the acid vapours are thus condensed, the smoke pa.s.sing off by a chimney connected with the towers. The diluted acid solution thus formed is concentrated by the aid of the apparatus shown in section in figs. 1, 2, and 3.

This apparatus consists of several cast-iron cylinders, 57 feet long by 27 feet in diameter, closed in the same manner as gas retorts, by lids luted with clay. One of the lids has an opening _o_, into which is fitted the stoneware or leaden pipe _a_, conveying the hydrochloric acid to the condensing apparatus. The other, or posterior lid, is also provided with an opening _d_, through which is pa.s.sed the tube of a leaden funnel, so that after the retort is filled with salt sulphuric acid may be poured in.

The construction of the furnace in which two retorts are usually placed, permits the flame of the fire at O to play round the cylinders before reaching the flue leading to the chimney F. B is an arch over the furnace.

The first stage of the operation consists in filling each cylinder with 330 lbs. of salt. The lids or covers are then luted on, and the fire is kindled. The requisite quant.i.ty of strong sulphuric acid is next poured into the retort, and the funnel having been withdrawn from D, the hole is covered by a clay plug.

[Ill.u.s.tration: FIG. 1.]

As soon as the reaction is over, the 396 lbs. of sulphate of soda produced are removed, and the operation repeated.

The condensation apparatus 1 and 3 is composed of rows of Woulfe's bottles, partly filled with water, care being taken to place the first pairs of these bottles in a tank of cold water.

The condensation of the last portions of hydrochloric acid gas is effected either by the aid of the c.o.ke columns, or in leaden chambers, into which fine jets of cold water are injected on all sides.

"A saturated solution of hydrochloric acid in water has the specific gravity of 121; and when heated in a retort, loses at first hydrochloric acid gas, but after a time an aqueous acid distils over, at the ordinary atmospheric pressure, containing 2022 per cent. of hydrochloric acid, and boiling constantly at 110 C. If the distillation be conducted under diminished pressure, the liquid boils at a lower temperature, and attains a composition which is different for each boiling point; hence the dilute acids thus obtained by boiling the solution of hydrochloric acid gas in water, cannot be considered as definite compounds of hydrochloric acid and water."[348]

[Footnote 348: Roscoe and Dittmar.]

[Ill.u.s.tration: FIG. 2.]

[Ill.u.s.tration: FIG. 3.]

Commercial hydrochloric acid is usually of a yellow colour owing to its being contaminated with iron. It also very frequently contains sodium, a.r.s.enic, sulphuric and sulphurous acids, and free chlorine.

Pure aqueous solution of hydrochloric acid should leave no residue upon evaporation; it should give no precipitation of ferric oxide when saturated with ammonia, sulphuretted hydrogen should cause no turbidity in it; if diluted with three or four times its volume of water, and chloride of barium be added, no white cloud or precipitate should form in the mixture; nor should the acid, if pure, discolour a fluid made faintly blue with iodide of starch.

Hydrochloric acid is largely consumed in the manufacture of chlorine, sal ammoniac, chloride antimony, glue, phosphorus, in the preparation of carbonic acid for the manufacture of artificial mineral waters, in beet-root sugar works, hydro-metallurgy, and alone, or mixed with nitric acid, for dissolving various metals.[349] See ACIDS, EFFECTS OF VEGETATION ON, CHLORINE.

[Footnote 349: Wagner.]

=HYDROCHLORIC ETHER.= (C_{2}H_{5}Cl.) _Syn._ ETHYL CHLORIDE, CHLORIDE OF ETHYL. This ether may be obtained either by saturating alcohol with hydrochloric acid gas, and then distilling at a gentle heat, or by distilling a mixture of three parts of oil of vitriol, two of alcohol, and four of fused chloride of sodium; the retort is in either case connected with a tubulated receiver, surrounded by water at a temperature of about 68 Fahr., in which most of the alcohol and water which pa.s.s over during the operation become condensed, whilst the ether escapes in the form of vapour through a bent tube, which is inserted into the tubulure of the receiver, and pa.s.ses to the bottom of a flask kept cool with ice. The liquid which is condensed in the flask must be rectified from calcic chloride.

Hydrochloric ether is a colourless liquid, having a specific gravity at 32 Fahr. of 0921, and a boiling point of 519 Fahr. The specific gravity of its vapour is 2219. It has an ethereal, penetrating, somewhat garlicky odour. It is sparingly soluble in water, but readily so in alcohol. These solutions fail to give a precipitate with argentic nitrate.

=HYDROCYANIC ACID.= (HCN HCy.) _Syn._ PRUSSIC ACID, HYDRIC CYANIDE, CYANHYDRIC ACID. Hydrocyanic acid was discovered by Scheele; but its nature and chemical properties were first investigated by Gay-Lussac.

_Sources._ This acid is found in water distilled from the kernels of the apricot, the peach, the plum, and cherry, the leaves of the laurel, and some other shrubs. The kernels of the bitter almond also yield it by distillation, mixed with an essential oil. The juice of the tapioca plant (the _Jatropha manihot_) likewise contains it. Many nitrogenous substances, when submitted to destructive distillation, also evolve hydrocyanic acid. Crystallised ammonic formiate subjected to heat in a retort yields a vapour which, pa.s.sed through a red-hot tube, decomposes into this acid and water. Another method by which it may be obtained, consists in sending a current of dry sulphuretted hydrogen gas through a long tube filled with cyanide of mercury; and very recently it has been obtained by the direct combination of nitrogen and acetylene gas, by adding one volume of the former to two of the latter, and pa.s.sing a series of electric sparks through the mixture, the gases combining without condensation. Lastly, it is yielded when a metallic cyanide or ferrocyanide is decomposed by an acid, this latter being the means by which it is invariably procured.

1. ANHYDROUS HYDROCYANIC ACID may be prepared by Wohler's plan, which is as follows:--A crude pota.s.sium cyanide is prepared by fusing eight parts of the dried pota.s.sium ferrocyanide with three of pota.s.sium carbonate and one of charcoal.

The fused ma.s.s is treated with six times its weight of water in a well-closed vessel; the clear liquid is decanted from the iron, which it is the object of this operation to separate, and is poured into a retort: sulphuric acid, diluted with an equal weight of water, is gradually added in the proportion of one part of oil of vitriol to two parts of the cyanide. At first the distillation proceeds spontaneously from the heat developed by the admixture of sulphuric acid with the water. In order to condense the acid, the products are made to pa.s.s through a long U-shaped tube, immersed in cold water and filled with calcic chloride, with the exception of the first fourth of the tube, which contains fragments of the crude pota.s.sium cyanide; to the bent tube is attached a second delivery tube, which pa.s.ses to the bottom of a bottle cooled with ice and salt. The calcic chloride in the syphon tube retains the moisture, and the pota.s.sic cyanide any sulphuric acid that might chance to pa.s.s over, whilst the hydrocyanic acid collects in the anhydrous state in the cooled receiver.

Trautwein recommends it to be prepared by the dehydration of the strong aqueous acid, by means of fused and pulverised chloride of calcium.[350]