Cooley's Cyclopaedia of Practical Receipts Volume I Part 280

[Footnote 350: The details of this process are given in 'Watt's Chemical Dictionary.']

? The observance of the greatest care and caution are necessary in the preparation of this most potent poison. The operation is most safely performed in winter. The apparatus should be so arranged as to allow of any vapours given off being carried from the operator by a brisk current of air.

_Prop._ At ordinary temperatures anhydrous hydrocyanic acid is a colourless liquid, having a specific gravity of 07058 at 446 Fahr. It is very inflammable, burning with a violet flame resembling that of cyanogen, but somewhat whiter in colour. It is soluble in all proportions in water, the resulting mixture being lighter than that fluid, and miscible with alcohol. It is very feebly acid; pota.s.sic cyanide always having an alkaline reaction. Red oxide of mercury is readily dissolved by it, and when added to a solution of argentic nitrate it precipitates white flocculi of cyanide of silver. Anhydrous hydrocyanic acid is an extremely volatile liquid; if a drop be let fall on a gla.s.s plate, part of it becomes frozen by the cold produced by its own evaporation.

2. PREPARATION OF AQUEOUS HYDROCYANIC ACID.

_a._ _From hydrated ferrocyanide of pota.s.sium._--By heating it in a gla.s.s retort with oil of vitriol and water, Everitt states that the best proportions are nearly ten parts of the salt to seven of oil of vitriol (diluted with any convenient amount of water). Adopting these proportions, 4224 parts of ferrocyanide of pota.s.sium yield 81 parts of hydrocyanic acid. The greater part of the hydrocyanic acid pa.s.ses over at the beginning of distillation, at a temperature a little above 212 Fahr.; and when the residual liquid reaches a higher temperature, the water (which then contains but little hydrocyanic acid) is then carried over. It is therefore necessary to employ a good condensing apparatus, or the hydrocyanic acid which pa.s.ses over at first will for the most part be dissipated in vapour mixed with the air of the apparatus. This loss may also be obviated by placing water in the receiver. The residue need not be boiled down to dryness; it will be found best to distil off from two thirds to three fourths of the liquid, according to the amount of water present.

It is not necessary to dissolve the ferrocyanide in water previous to adding the sulphuric acid, as it readily dissolves in the water during the process of distillation.

Three conditions are important to be observed in the arrangements of the apparatus:--1. The mixture in the retort should not be allowed to spirt over. 2. It should contain but little air. 3. It should present the greatest possible amount of surface to be cooled.

If sulphate of pota.s.sium and prussian blue are spirted over into the distillate, this must be carefully rectified over a small quant.i.ty of magnesia, chalk, or carbonate of barium.

_b._ _From cyanide of pota.s.sium_ (without distillation).--To a solution of nine parts of tartaric acid in sixty parts of water, contained in a well-stoppered bottle nearly filled with it, four parts of pure cyanide of pota.s.sium are added; the vessel is shaken, frequently dipped into cold water, and then left in the cold for twelve hours; and the aqueous hydrocyanic acid, which contains but a very small quant.i.ty of tartrate of pota.s.sium, is poured off from the crystallised tartrate.[351] This acid contains 36 per cent. of anhydrous hydrocyanic acid.

[Footnote 351: 'London Med. Surg. Journ.,' vi, 524.]

_c._ _From cyanide of mercury._--126 (accurately weighed) parts of cyanide of mercury are agitated with at least 28 parts of iron filings, in a well-stoppered bottle, containing 49, or rather more, parts of oil of vitriol, diluted with a considerable quant.i.ty of water. The agitation is continued until a portion of the liquid taken out is not blackened by sulphuretted hydrogen.

The solution, decanted from the iron and mercury, is then placed in a retort and distilled; the acid coming over at a gentle heat. Excess of iron accelerates the decomposition.

_d._ _From cyanide of silver._--Everitt recommends 200 parts of pure cyanide of silver to be shaken up with 240 parts of hydrochloric acid of specific gravity of 1129, and when the decomposition is complete, the hydrocyanic acid to be separated from the chloride of silver by decomposition.

This hydrocyanic acid may contain a small quant.i.ty of hydrochloric acid, a not very objectionable admixture, since it r.e.t.a.r.ds decomposition. It possesses the advantage of definite strength.

_Prop._ The aqueous is very similar in properties to the anhydrous acid, differing in taste, odour, poisonous and combustible properties, according to its degree of concentration. Like the anhydrous, the aqueous acid decomposes, but not so readily; when perfectly pure, becoming brown, and at last black. As before stated, a little free mineral acid a.s.sists to preserve it. It should be always kept in a dark place.

_Detection and estimation of hydrocyanic acid and soluble cyanides._--The presence of hydrocyanic acid, indicated by the characteristic smell, which is given off by the contents of the stomach, or of any fluid containing it (provided this is not disguised by any substance of stronger odour) may be confirmed by the following tests:

1. To the filtered suspected fluid add a slight excess of caustic potash, and then a solution containing ferrous and ferric sulphates. If hydrocyanic acid, or a soluble cyanide be present, upon the addition of an excess of hydrochloric acid the liquid turns to a blue colour (more or less intense according to the quant.i.ty of acid present), owing to the formation of Prussian blue.

2. Add the suspected fluid solution of nitrate of silver; if hydrocyanic acid be present, a white cyanide of silver is formed, which is nearly insoluble in cold nitric acid, but is soluble in ammonia and cyanide of potash, and which, when heated to redness, gives off the inflammable violet-flamed cyanogen.

3. Acidulate a small quant.i.ty of the suspected liquid with a few drops of hydrochloric acid, and place it in a watch-gla.s.s; then invert a second watch-gla.s.s, moistened with a drop of solution of ammonic sulphide over this. After a few minutes remove the upper watch-gla.s.s, and evaporate the liquid to dryness over a water bath; let the dry residue be treated with a drop of a weak solution of ferric chloride. If hydrocyanic acid be present, a blood-red colour is produced, owing to the formation of red ferric hydrocyanide, which may be discharged by chloride of mercury; a reaction which distinguishes it from a similar colour given by meconic acid.

Where large quant.i.ties of material have to be examined, it is desirable that the acid should be distilled off by the heat of a water-bath, acidulating the liquid with tartaric acid if it be alkaline. The distillate is then to be tested by any of the above methods.

_Antidotes._--Give a scruple of carbonate of potash dissolved in about an ounce of distilled water, and directly afterwards, ten grains of sulphate of iron, also dissolved in the same quant.i.ty of distilled water, to which should be added one drachm of tincture of perchloride of iron. Whilst this is being prepared, and subsequently, apply cold affusion to the head and neck, artificial respiration, and, if practicable, give strong coffee and brandy. A more ready remedy is ammonia, given both internally and applied to the nostrils.

=Hydrocyanic Acid, Diluted.= _Syn._ ACIDUM HYDROCYANIc.u.m DILUTUM. (B. P.) The 'British Pharmacopia' gives the following simple directions for the preparation of this acid:--

Dissolve two and a quarter ounces (avoir.) of ferro-cyanide of pota.s.sium in ten fluid ounces of distilled water, then add one fluid ounce of sulphuric acid, previously diluted with four fluid ounces of distilled water, and cooled. Put them into a retort and adapt this to a receiver, containing eight fluid ounces of water, which must be kept carefully cold.

Distil with a gentle heat until the fluid in the receiver measures seventeen fluid ounces. Add to this three fluid ounces of the water, or as much as may be sufficient to bring the acid to the required strength of two per cent. by weight.

_Prop._ Specific gravity, 997. 100 grains, or 110 minims, precipitated with a solution of nitrate of silver, give a precipitate of cyanide of silver, which when dried, weighs 10 grains. 270 grains rendered alkaline by liquor sodae, require a 1000 grain measures of volumetric solution of nitrate of silver, before a permanent precipitate begins to form.

_Antidotes._ See HYDROCYANIC ACID.

=Hydrocyanic Acid, Scheele's.= _Syn._ ACIDUM HYDROCYANIc.u.m SCHEELII. The original process of Scheele does not yield an acid of uniform strength, and is probably never followed. It is therefore impossible to state precisely what is intended when Scheele's acid is prescribed, or to understand why it should be preferred by certain physicians to the British Pharmacopia preparation, which is of a known and definite strength. As prepared by different makers it has been found to contain from three to five per cent. of anhydrous acid. The following is Scheele's process:--

Mix two ounces of Prussian blue, with six ounces of red precipitate of mercury, and add six ounces of water. Boil for some minutes, constantly agitating; pour the whole on a filter and wash the residuum on the filter with two ounces of hot water, which is to be added to the filtered liquor.

Add to this an ounce and a half of clean iron filings, and three drachms of sulphuric acid; shake well and let it settle; then pour the clear liquor into a retort, and distil a fourth part into a receiver well luted and kept cold.

=HYDROFLUORIC ACID. (H. F.)= _Syn._ HYDRIC FLUORIDE, HYDROGEN FLUORIDE.

_Prep._ 1. From _fluor-spar_ (free from silica and metallic sulphides) and oil of vitriol. The fluor-spar being reduced to fine powder and placed in a leaden retort, is mixed with twice its weight of concentrated oil of vitriol, and on applying heat, an acid and highly acid vapour distils over, which condenses to a liquid if pa.s.sed into a receiver of the same metal, standing in a freezing mixture at a temperature of 4 Fahr. Louyet has shown that the liquid acid, obtained as above, is not (as once believed) anhydrous.

2. From the double fluoride of pota.s.sium and hydrogen. Fremy first renders the salt anhydrous by careful drying; and by the subsequent application of a strong heat, expels the equivalent of hydrofluoric acid contained in it; condensing it into a colourless, mobile, very volatile liquid by the application of a freezing mixture of ice and salt.

3. By decomposing plumbic fluoride by dry hydrogen.

_Prop._ The strong, aqueous, hydrofluoric acid obtained by the action of oil of vitriol on fluor-spar, is a densely fuming, volatile, colourless liquid, which boils at 60 F., and remains unfrozen at 4. It combines with water so greedily, and evolves so much heat in doing so, as to give rise to a hissing noise like that produced when a red-hot iron is plunged into cold water. In a concentrated form it has a specific gravity of 1060. Brought into contact with animal matter of any kind it instantly destroys it, the smallest drop on the skin producing a deep and painful wound; hence the necessity of the greatest care in its preparation. With the exception of platinum, gold, silver, mercury and lead, hydrofluoric acid, when diluted, dissolves the metals, the metal when it undergoes solution, displacing hydrogen. Pota.s.sium decomposes the strong acid with explosion.

In both the gaseous and fluid form hydrofluoric acid is largely consumed for etching on gla.s.s; and this property const.i.tutes one of its most available and reliable tests. The test may be conveniently applied as follows:--

Cover a small piece of window gla.s.s or a watch gla.s.s with a thin layer of wax, sc.r.a.ping away a very small portion by means of a sharply pointed instrument, and then expose the gla.s.s for a short time to the vapour of the acid, given off when the materials are heated in a small leaden saucer or platinum crucible; on removing the wax with a little turpentine, the marks on the gla.s.s caused by the hydrofluoric acid will be distinctly perceived.

=HYDROFLUOSILIC'IC ACID.= (_{4}HF.SiF_{4}.) FLUORIDE OF SILICON AND HYDROGEN. _Prep._ From powdered fluor-spar, and siliceous sand or powdered gla.s.s, of each 1 part; concentrated sulphuric acid, 2 parts; mix in a gla.s.s retort, apply a gentle heat, and pa.s.s the evolved gas (fluoride of silicon) into water. Decomposition ensues, silica being deposited in a gelatinous state, and hydrofluosilicic acid remaining in solution. This acid liquor, which is a double fluoride of silicon and hydrogen, is used as a test for barium and pota.s.sium, with which it forms nearly insoluble precipitates.

=HY'DROGEN. (H.)= _Syn._ HYDROGENIUM, L. An elementary body discovered by Cavendish in 1766. It has been found existing in an uncombined state in the gases evolved from the solfataras of Iceland. Combined with oxygen, it const.i.tutes water, and in this form is extensively distributed through earth, air, and ocean. It is an important const.i.tuent of all organised tissues.

_Prep._ Hydrogen is always obtained for experimental purposes by the deoxidation of water, by one or other of the following methods:--

1. A tube of iron or porcelain (a gun-barrel, for instance) containing a quant.i.ty of iron turnings or sc.r.a.ps of iron, is fixed across a furnace, so that its middle portion may be made red-hot; to the one end is attached a retort or other vessel containing water, and to the other a bent tube connected with a pneumatic trough or gasometer. The tube being now heated to redness, and the water in the retort brought into a state of brisk ebullition, the evolved steam suffers decomposition; the oxygen being absorbed by the iron, and the hydrogen escaping into the gas receiver.

2. Sulphuric acid (oil of vitriol), diluted with 6 or 8 times its bulk of water, is poured on granulated zinc (or sc.r.a.ps of iron) placed in a retort or gas bottle; hydrogen is evolved and is collected, as before.

_Obs._ This is the most convenient method of preparing hydrogen, and the one usually adopted in the laboratory. To ensure the gas being quite pure, distilled zinc is employed, and the gas is pa.s.sed, first through a concentrated solution of pure pota.s.sa, then through a solution of nitrate of silver, and, lastly, through strong oil of vitriol, or over fragments of chloride of calcium. When hydrogen is prepared from crude zinc, it has a slight smell; and when from iron, its odour is often strong and disagreeable.

_Prop._ Gaseous; colourless; tasteless; odourless (when pure); combustible; sp. gr. 06935, being 16 times lighter than oxygen gas, and 144 times lighter than atmospheric air. 100 cubic inches, at 60 Fahr.

and 30 inches of the barometer, weigh 21371 (say 214) gr.; 1 gr.

occupies 466 inches. It is very readily inflamed, even by a red-hot wire.

It burns with a scarcely visible flame. Mixed with atmospheric air or oxygen, it explodes with extreme violence on the approach of flame, or sudden compression. One measure of hydrogen and 5 of atmospheric air, and 2 of hydrogen and 1 of oxygen, are the proportions that explode with the greatest violence. The combination of hydrogen and oxygen, when mixed, is brought about by the heat of a red-hot solid or a flame, by the electric spark, and by the presence of spongy platinum, the black powder of platinum, clean platinum foil, and some other substances. A jet of hydrogen burnt in oxygen gas, or a jet of these gases (mixed) burnt in the air, with proper precautions, produces a most intense heat. Water absorbs about 2% by volume of hydrogen.

Hydrogen has recently been liquefied and even solidified.

_Tests._ It is recognised by--its combustibility;--the pale colour of its flame;--producing water only when burnt in air or oxygen;--extinguis.h.i.+ng the flame of other bodies; and--exploding when mixed with half its volume of oxygen, and fired.

_Uses, &c._ Pure and uncombined hydrogen is not employed in the arts.

Inhalations of this gas have, however, been occasionally used in medicine.

Dr Beddoes recommended them in phthisis. In combination, the uses of hydrogen are almost numberless. Combined with oxygen, it forms water; with chlorine, hydrochloric acid; with fluorine, hydrofluoric acid; with cyanogen, hydrocyanic acid; with carbon, innumerable hydrocarbons; with nitrogen, ammonia; with sulphur, sulphuretted hydrogen--in fact, an enumeration of the valuable compounds which it enters into would occupy many pages of this work. From its extreme lightness it has been used to fill balloons, but coal-gas is now commonly employed for this purpose. On its property of inflaming in contact with spongy platinum is arranged the popular little instrument for the production of instantaneous light (DOBEREINER'S LAMP) sold by the philosophical instrument makers. The chemist avails himself of the great heat developed by its combustion in oxygen in the formation of the OXYHYDROGEN BLOWPIPE.

Some of the compounds of hydrogen are noticed _below_; the others under their respective names.

=Hydrogen, Antimo"niuretted.= (SbH_{3}.) _Syn._ ANTIMONETTED HYDROGEN, HYDRIDE OF ANTIMONY, STIBAMINE; HYDROGENIUM ANTIMONIATUM, L. A gaseous compound of antimony and hydrogen, prepared by dissolving an alloy of antimony with a large excess of zinc in hydrochloric or dilute sulphuric acid. It has never been obtained pure, a variable proportion of free hydrogen being always present. It burns with a bluish-white flame, giving rise to dense fumes of teroxide of antimony, and when conducted through a red-hot tube, or the flame is thrown on a cold surface, as a porcelain plate, metallic antimony is deposited. This gas is a deadly poison when inhaled. See a.r.s.eNIOUS ACID.

=Hydrogen, a.r.s.en"iuretted.= (AsH_{3}.) _Syn._ a.r.s.eNETTED HYDROGEN, HYDRIDE OF a.r.s.eNIC, a.r.s.eNAMINE; HYDROGENIUM a.r.s.eNIURATUM, L. A gaseous compound of a.r.s.enic and hydrogen.