Part 44
_Prop._ Very brittle, so much so that it may be easily powdered in a mortar; lustre highly metallic; colour steel-grey or bluish-white; texture crystalline; crystals rhombohedrons; sublimes, without fusion, at 356 to 360° Fahr., (and slowly at lower temperatures), in close vessels unaltered, but when exposed to the air with conversion into arsenious acid; at a higher temperature, in open vessels, it burns with a pale-blue flame. Its vapour or fumes have a characteristic alliaceous odour; it is slowly oxidised and dissolved by boiling water; but may be preserved unchanged in pure cold water; it rapidly tarnishes in the air, particularly when moist, a black film, consisting of metallic arsenic and arsenious acid forming on its surface; with chlorine, iodine, sulphur, and hydrogen, it unites to form definite compounds. With oxygen it forms acids, but no basic oxide. It combines with the metals in a similar manner to sulphur and phosphorus, the latter of which it resembles in many respects. These compounds are termed AR'SENIDES, formerly ARSENIURETS. Sp. gr. 5·7 to 5·9; sp. gr. of vapour, 1·0362.
_Uses, &c._ With copper it forms a white alloy (PACKFONG); and it is added to some other alloys to increase their whiteness, hardness, and fusibility. In _medicine_ it is only used in combination. In the metallic state it is inert; but, from its great affinity for oxygen, it rapidly becomes oxidised and poisonous; and hence acts as a powerful poison when swallowed, or when rubbed on the skin. Its fumes are also highly poisonous. See ARSENIOUS ACID (and _below_).
=Arsenic, Tribro'mide of.= AsBr_{3}. _Syn._ TERBRO'MIDE OF ARSENIC, SESQUIBRO'MIDE OF A.; ARSEN'ICI BROMI'DUM, L. _Prep._ Add metallic arsenic, in powder, cautiously and in a very small quantity at a time, to pure bromine, contained in a vessel set in ice or a freezing mixture, until light ceases to be emitted; then cautiously distil into a well-cooled receiver.
_Prop., &c._ Solid below 68° Fahr.; above it, a yellowish fuming liquid, which boils at 428° Fahr.
=Arsenic, Trichlo''ride of.= AsCl_{3}. _Syn._ CHLO''RIDE OF A., ARSEN'ICI TERCHLORI'DUM, &c., L. _Prep._ 1. From a mixture of white arsenic, 1 part; and bichloride of mercury, 6 parts; both in powder, carefully distilled into a well-cooled receiver.
2. Gently boil powdered white arsenic for some time in hydrochloric acid to which a little nitric acid has been added; then concentrate cautiously by evaporation, and distil as before. It is also produced, with the disengagement of heat and light, when powdered metallic arsenic is thrown into gaseous chlorine.
_Prop., &c._ A colourless, volatile, highly poisonous liquid, decomposed by water into arsenious acid and hydrochloric acid. It has been employed as a caustic in cancer and venereal warts; but its use requires the greatest caution.
=Arsenic, Flu'oride of.= AsF_{3}. _Syn._ ARSENIC TRIFLUORIDE, TERFLU'ORIDE OF ARSENIC. A fuming volatile liquid, prepared as the bromide.
=Arsenic, Trii'odide of.= AsI_{3}. _Syn._ TERIODIDE OF ARSENIC, IODIDE OF ARSENIC; ARSEN'ICI IODI'DUM, A. TERIODI'DUM, L.; ARSENIC IODURE, &c., Fr. _Prep._ 1. From finely-pulverised metallic arsenic, 2 parts; iodide, 11 parts; mixed and gently heated in a bent glass tube, or a suitable retort, until combination is complete; the heat being then raised, and the sublimed iodide collected, and at once put into a well-stopped phial.
2. Arsenic, in fine powder, 1 part; iodine, 5 parts; triturate them together, place the mixture in a small flask or retort just large enough to contain it, and apply a gentle heat until liquefaction is complete, avoiding the formation of iodine vapour; when the odour of iodine is no longer perceptible, and the mass assumes a reddish-yellow colour and crystallises on the sides of the vessel, the operation is complete, without having recourse to sublimation. A very easy and excellent process.
_Prop., &c._ A deep orange-red, crystallisable solid; soluble in water, and highly volatile and poisonous. Its aqueous solution yields the iodine unchanged by rapid evaporation, but when slowly concentrated and set aside, white pearly plates are obtained, consisting of arsenious acid and the teriodide. As a medicine it combines the properties of both arsenious acid and iodine, but its use requires great caution. It has been successfully employed by Dr A. T. Thomson, Biett, and others, in obstinate skin diseases (lepra, impetigo, herpes, lupus, psoriasis, &c.), and in real or stimulated cancer.--_Dose_, 1/16 to 1/12 gr. (in pills or solution), gradually increased to 1/6 or even 1/3 gr. (A. T. Thomson.) Externally, 2-1/2 gr., to lard 1 oz.; of which 1 dr. may be used at a time. (Biett.)
=Arsenic, Disulphide of.= As_{2}S_{2}. _Syn._ ARSENIC BISULPHIDE, BISUL'PHIDE OF A., RED SUL'PHIDE OF A., &c., REALGAR; RÉALGAL, ARSENIC ROUGE SULFURE, ORPIN ROUGE, &c., Fr.; ROTHES SCHWEFELARSENIK, &c., Ger. This substance is found native at Solfaterra, near Naples, and in several other volcanic districts; but that of commerce is often prepared by distilling arsenical pyrites, or a mixture of sulphur and white arsenic, &c., in the proper proportions, as noticed under REÄLGAR and RED PIGMENTS.
_Prop., &c._ A fusible, volatile substance; scarlet or ruby-red in mass, but orange-red in powder, by which it is distinguished from cinnabar; crystals, oblique rhombic prisms. Sp. gr. 3·3 to 3·6. Its chief use is as a pigment and in pyrotechny to make white fire. The factitious sulphide has not the rich colour of the native mineral, whilst it is much more poisonous. It is improved by re-sublimation.
=Arsenic, Trisul'phide of.= As_{2}S_{3}. _Syn._ TERSUL'PHIDE OF ARSENIC, YELLOW SUL'PHIDE OF A., SESQUISUL'PHIDE OF A., OR'PIMENT; A. SESQUISULPHURE'TUM, ORPIMEN'TUM, L.; ORPIMENT, SULFURE JAUNE D'ARSENIC, &c., Fr.; AURIPIGMENT, OPERMENT, RAUSCHGELB, Ger. This sulphide, like the last, is found ready formed in nature; and is prepared artificially, by sublimation, from a mixture of arsenious acid and sulphur, as noticed under ORPIMENT and YELLOW PIGMENTS. It also falls as a precipitate when a stream of sulphuretted hydrogen gas is passed through an acid solution of arsenious acid or of an arsenite.
_Prop., &c._ Golden-yellow crystalline lumps, or a fine golden-yellow powder; crystals, right rhombic prisms; volatile; fusible; very soluble in pure alkalies, by which it is distinguished from sulphide of cadmium; and from trisulphide of antimony by being soluble in hydrochloric acid. The factitious sulphide (KING'S YELLOW) of the shops often contains 80 to 90% of white arsenic; and is, therefore, much more poisonous than the native trisulphide. Sp. gr. (native) 3·44 to 3·60.
_Use, &c._ As a dye, as a pigment, and as an ingredient in fireworks, and in some depilatories. Silk, woollen, or cotton goods soaked in a solution of pure orpiment in ammonia, and then suspended in a warm apartment or stove-room, rapidly lose their ammonia, and become permanently dyed of a superb yellow colour. The native sulphides (both red and yellow) are much less soluble, and hence less poisonous, than those prepared artificially. They also possess the richest colour; and are, therefore, preferred by artists and dyers. In former times, orpiment, like realgar, was employed in medicine. See ARSENIC.
=Arsenic, Pentasul'phide of.= As_{2}S_{5}. _Syn._ SULPHARSEN'IC ACID, &c.; ARSEN'ICI PENTASULPHURE'TUM, &c., L. When a stream of sulphuretted hydrogen is transmitted for some time through a solution of arsenic acid, a precipitate of the PENTASULPHIDE is deposited after some hours' repose. Its formation is accelerated by boiling the liquid.
_Prop., &c._ It greatly resembles the tersulphide in its appearance and general properties.
=Arsenic, White[double-dagger].= See ARSENIOUS ANHYDRIDE.
=Arsenic, Yell'ow.= Trisulphide of arsenic.
=ARSENIC ACID.= H_{3}AsO_{4}. _Syn._ ACIDUM ARSEN'ICUM, L.; ACIDE ARSÉNIQUE, Fr.; ARSENICSÄURE, Ger.
_Prep._ 1. Arsenious acid, in fine powder, 2 parts; concentrated nitric acid, 6 parts; hydrochloric acid, 1 part; mix in a flask or tubulated retort, and digest, with heat, until solution is complete; after repose, decant the clear portion and evaporate, to the consistence of a thick syrup.
2. Dissolve arsenious acid in hot hydrochloric acid, and when the solution is cold add concentrated nitric acid, in small quantities at a time, until red vapours cease to be evolved, then proceed as before.
_Prop._ Thick syrup, occasionally forming clear transparent crystals, very deliquescent, readily soluble in water, and converted by heat into the anhydrous acid. Extremely poisonous.
=Arseniates.= _Prep._ Most of the metallic arseniates may be formed by adding a solution of a soluble salt of the metal to another of an alkaline arseniate, as long as a precipitate falls; which must be collected, washed, and dried. The alkaline arseniates may be prepared by adding the base or its carbonate to a solution of the acid, to alkaline reaction, and then evaporating and crystallising the liquid.
_Prop., &c._ The arseniates of the alkalies are soluble in water; those of the earths and metals insoluble, except in acids. They are isomorphous with the corresponding phosphates.
_Tests._ Nitrate of silver added to the solution of an arseniate gives a highly characteristic reddish-brown precipitate, which distinguishes it from arsenious acid. Nitrate of lead gives a white precipitate, and the salts of copper greenish-blue ones. Pure lump-sugar dissolved in an aqueous solution of this acid becomes, in a few hours, of a reddish colour, and afterwards of a magnificent purple. Heated with charcoal it evolves a garlic-like odour, and is reduced to the metallic state. The suspected liquid being treated with sulphurous acid and boiled for a short time, the arsenic acid loses oxygen and is converted into arsenious acid, which may be tested for as such. Sulphuretted hydrogen does not precipitate a solution of arsenic acid, or an acidified arseniate, until after the lapse of several hours; and alkaline and neutral solutions not at all.
=ARSENIC ANHYDRIDE.= As_{2}O_{5}. _Syn._ ANHYDROUS ARSENIC ACID, ARSENIC ACID; ACIDUM ARSENICUM, L.; ACIDE ARSÉNIQUE, Fr.; ARSENIKSÄURE, Ger. Best prepared by igniting the arsenic acid, in a platinum crucible, at a low red heat, as long as water is given off.
_Prop._ White deliquescent substance, and violent poison, readily soluble in water to the acid.
=ARSENIOUS ACID.= See ARSENIOUS ANHYDRIDE.
=ARSE''NIOUS ANHYDRIDE.= As_{2}O_{3}. _Syn._ AR'SENIOUS ACID, AR'SENIC, WHITE A.; ACIDE ARSÉNIEUX, ARSENIC BLANC, OXYDE, Fr.; ARSENIGSÄURE, ARSENICHSTE S., Ger.; ARSENICO BIANCO, It.; A. BLANCO, Sp. The arsenic, or white arsenic, of the shops.
_Sources._ The white arsenic of commerce is principally imported from Germany, where it is obtained in the process of roasting arseniuretted cobalt ores, in making zaffre. At Altenburgh it is procured from arsenical iron pyrites (mispickel); and at Reichenstein from native arsenide of iron. About 900 to 1000 tons are also annually collected at Cornwall, being principally a secondary product of the process of roasting grey copper ore and white mundic. The British arsenic works in that county are perhaps the finest in the world. The usual plan is to roast the powdered ore in muffle-furnaces; by which its arsenic is converted into arsenious anhydride, which escapes as vapour (smelting-house smoke), and passing into the condensing-chambers, is deposited in a pulverulent state, forming the flowers of arsenic, or rough white arsenic, of the smelters, (the giftmehl or poison-flour of the Germans). The crude article obtained in this way is purified by re-sublimation in suitable iron pots or other iron vessels, before it is fit for sale. It then forms a semi-transparent vitreous cake, which gradually becomes opaque, and of snowy whiteness, by exposure to the air, and at length acquires a more or less pulverulent state on the surface.
In Silesia the crude arsenious anhydride obtained from arsenical pyrites is refined by sublimation as follows:--For this purpose the cast-iron vessels (_a_) are employed. Upon these are placed iron rings or collars (_b_, _c_, _d_) and a hood (_e_), communicating by means of tubes with a series of chambers, of which the first only is shown in _i_. The flanges of the cast-iron collars and all other joints having been thoroughly luted, the fire is lighted and the heat so increased as to cause the semi-fusion of the arsenious anhydride, which, after cooling, exhibits a peculiarly porcelain-like appearance, at first being as transparent as glass.
_Prop._ Crystals (obtained by careful sublimation, or by cooling a boiling aqueous solution), usually transparent, regular octahedrons (fig. 1), but sometimes, though rarely, assume the form of tetrahedrons (see 2). When prepared on the large scale it forms large, glassy, colourless or yellowish-white, transparent or semi-transparent cakes or porcelain-like masses (vitreous arsenious anhydride, glacial a. a.), which soon becomes opaque on their exterior, and often friable and pulverulent; odourless; volatilises at 380° Fahr.; fumes odourless, unless carbonaceous organic matter be present, when they smell strongly like garlic; heated under pressure it liquefies and forms a transparent glass; taste faintly sweetish, with a slight acidity and astringency, not perceived until some minutes after being swallowed. The opaque variety is soluble in 80 parts of water at 59° Fahr., and 7·72 parts of boiling water; but on cooling to 60°, only about one third of this quantity continues in solution. The transparent variety is soluble in 103 parts of water at 59°, and 9·3 parts of boiling water. Both soluble in alcohol, syrups, oils, and spirits, and freely so in alkaline lyes and hydrochloric acid; organic matter generally impedes its solution; solutions redden litmus; heated with organic matter it is reduced to the metallic state. Sp. gr. 3·5 (lowest opaque var.) to 3·8 (highest transp. var.).
=Arsenites.= True arsenious acid (HAsO_{2}) has never been obtained in a satisfactory condition, but its salts are readily obtained by dissolving arsenious anhydride in a solution of the base, or by double decomposition. They are generally white, nearly all insoluble, except those of the alkalies, and all soluble in acids.
_Tests, Detec., &c._ Owing to the importance of the subject, and for convenience and facility of reference, the leading tests for the arsenites and arsenious anhydride are noticed alphabetically below; to which a few general remarks on their application, under the various circumstances that occur to the chemist and toxicologist, are appended. When not otherwise stated, it is to be understood that they are to be applied to pure, or nearly pure and colourless solutions of arsenious acid or the arsenites. _Ammonio-nitrate of silver_ gives a well-marked yellow precipitate of arsenite of silver in an aqueous or arsenious anhydride solution which is soluble in ammonia and in dilute nitric acid.
_Crystallisation Test._--A very minute quantity of arsenious acid placed in a small tube (arsenic-tube), and heated in the flame of a spirit lamp, gives a crystalline sublimate, which collects on the cooler portion of the tube, and which, when examined by a pocket lens, is found to consist of sparkling octahedral crystals (see _engr._)
_Ellis's Test._--This is a modification of the 'nascent hydrogen test,' in which the suspected gas is passed through a tube containing slips of copper leaf or riband, or still better pure oxide of copper, gently heated; the end of the tube communicating with the atmosphere being drawn to a capillary size, at which the gas may be inflamed and tested, as in 'Marsh's Apparatus.' (See _engr._) If arsenic be abundant in the gas, the copper will be almost instantly covered over with a coating of metallic arsenic; and after continuing the heat for a few minutes it will present a beautiful silvery surface, and may then be submitted to further examination.
_Lassaigne's Test._ (Adopted by the French Academy.) This consists in passing the gas generated in the suspected liquid, through a solution of nitrate of silver. (See _engr._) When arsenic is present black flocculi of metallic silver are deposited, and arsenious acid remains in solution mixed with nitric acid and some arsenide of silver. The filtered liquor, treated with ammonia, will now give a characteristic yellow precipitate of arsenite of silver; or a little dilute hydrochloric acid may be cautiously added to precipitate any remaining nitrate of silver, and the liquid, after filtration, tested for arsenic either in a Marsh's apparatus, or with any of the liquid tests; or it may be evaporated to dryness, when its arsenious acid will be converted into arsenic acid by the nitric acid present, and will then be found to give the usual brick-red precipitate of arseniate of silver with a solution of the nitrate of that metal. See MARSH'S TEST.
_Marsh's Test._ Some of the suspected liquid is mixed with dilute sulphuric acid until strongly acid, and is then poured upon some pure granulated zinc, or clippings or other small pieces of zinc, previously placed in the apparatus; hydrogen gas is immediately evolved, and, if arsenic be present, unites with it, forming arseniuretted hydrogen gas, which escapes by the aperture _b_ (see _engr._), and may be recognised as follows:--
It possesses a garlic-like odour.
It burns with a bluish-white flame and emits a whitish smoke.
If a piece of window-glass, or a white porcelain plate or saucer, be held a short distance above the flame, a fine pulverulent film of arsenious acid is deposited on it. See (fig.) _above_.
If the cold plate be held in the flame, so as to slightly impede the combustion of the gas, a blackish-brown deposit of metallic arsenic is obtained, more or less deep, brilliant, and glistening. Both these deposits may be obtained simultaneously by holding nearly vertically over the flame a glass tube about 8 or 10 inches long and 3/8ths of an inch in diameter. See (fig.) _above_.
A solution of arsenious acid may be obtained by letting the flame play upon 3 or 4 drops of water placed on the under side of the piece of glass or china, to which the liquid tests may be then applied. Another plan is to apply drops of the liquid tests to the plate as above, and to let the flame play on them successively.
The true arsenical spot or film is of a blackish-brown colour, and generally of a very deep hair-brown, usually surrounded at the circumference, with a white film of arsenious acid; whilst that of antimony, which in some points is similar, is of a deep black colour, and but feebly lustrous, and, when viewed by transmitted light, appears smoky black; whereas an arsenical spot viewed in the same way appears brown. It is further distinguished from others by--Treated with concentrated nitric acid, it instantly disappears, leaving upon the surface of the liquid traces of the metal, which only dissolve on the application of heat. This solution, gently and carefully heated, leaves a white residuum, which, when cold, gives with a concentrated solution of nitrate of silver a dull-red precipitate of arseniate of silver.--The nitric solution treated with a few drops of sulphurous acid, and subsequently with sulphuretted hydrogen, gives a canary-yellow precipitate of trisulphide of arsenic, which readily redissolves, forming a colourless solution with ammonia.--The arsenical spot, when heated, is turned bright yellow by sulphuretted hydrogen, and is then readily dissolved, as before, by ammonia, and by its bicarbonate; whereas one of antimony is turned of a deep orange-red, or reddish-brown, by sulphuretted hydrogen, is not readily dissolved by ammonia, and is scarcely or not at all affected by bicarbonate of ammonia.--It is freely soluble in and removed by hypochlorite of soda; a reagent which does not affect antimonial spots. Heated by a flame of pure hydrogen an arsenical stain rapidly disappears. A mixed stain of antimony and arsenic does not disappear by the action of the last two reagents, and is shown to contain arsenic by the two first tests above. When hydrochloric acid is present zinc stains are sometimes formed, but they do not resemble those from arsenic. The flame which produces it is very pale blue or bluish-white; whereas antimoniuretted hydrogen burns with a pale green or greenish-yellow flame, and a white smoke, both of which are characteristic.
_Obs._ Marsh's test is admirable for its simplicity, delicacy, and trustworthiness, as well as for the ease of its application. It is adapted to all liquids, whether colourless or coloured, which are not so glutinous as to inconveniently froth during the extrication of the hydrogen.[79] Various modifications of the original apparatus have been proposed to obviate this difficulty; among which the one chiefly deserving notice is figured in the margin. It consists of a bent tube having two large bulbs blown in it, and fitted with a stop-cock and jet in the usual manner. In this case the grains or fragments of zinc are put into the lower bulb (_a_). It is, however, worthy of remark, that, with ordinary care and skill, a simple wide-mouthed bottle, furnished with a tube and cock, will often be found to answer quite as well as more costly apparatus; as the fluid is less liable to froth than in a narrow tube. Even a common quinine-phial, or a 4-_oz._ or 6-_oz._ medicine phial, fitted with a piece of glass tube of very small bore, or even with a piece of a common tobacco-pipe, for a burner (see _engr._), may be used when no more convenient instrument is at hand.
[Footnote 79: Animal tissues and liquids containing organic matter are best prepared for testing for arsenic by Marsh's test, in the following manner proposed by Odling:--The tissue, or the residue obtained by the evaporation of a liquid over a water-bath, is to be thoroughly dried at a temperature of about 212° F., then ground to powder or cut up into small pieces, next drenched with the strongest hydrochloric acid and allowed to stand twenty-four hours in a warm place, and finally distilled. The distillate will contain arsenic (if it existed in the material under examination) comparatively free from organic matter, and is, therefore, in a fit state to be introduced into Marsh's apparatus, as the organic matter, which is the cause of frothing, has been removed.]
A film of oil placed on the surface of the liquid tends considerably to lessen the frothing.