Cooley's Cyclopaedia of Practical Receipts Volume I Part 58

Finally, the author mentions that where paper is used with the silver solution we must not forget that the silver alone will after some time blacken the paper, especially if exposed to light; but this gradual change is very unlike the quick effect produced by a.r.s.eniuretted or antimoniuretted hydrogen. ('Chem. News,' x.x.xiii, 58-63.)

_Nascent Hydrogen Test._ The apparatus used may be similar to that figured in the _engr._ The plan followed in the laboratory of Giessen is to heat the long tube through which the gas pa.s.ses to redness in several parts, to produce distinct metallic mirrors; and then to remove the tube from the hydrogen apparatus and transmit a very feeble stream of dry sulphuretted hydrogen through it, the metallic mirrors being at the same time heated by means of a common spirit lamp from the outer towards the inner border or extremity. If a.r.s.enic alone is present, yellow trisulphide of a.r.s.enic is formed within the tube; if antimony alone is present, an orange-red or black trisulphide of antimony is produced; and if the mirror consists of both metals, the two sulphides appear side by side, the sulphide of a.r.s.enic, as the more volatile, lying invariably before the sulphide of antimony. If dry hydrochloric acid gas be now transmitted through the tube, without application of heat, no alteration will take place if sulphide of a.r.s.enic alone is present, even though the gas be transmitted through the tube for a considerable time. If sulphide of antimony alone is present, this will entirely disappear; and if both sulphides are present, the sulphide of antimony will immediately volatilise, whilst the yellow sulphide of a.r.s.enic will remain. If a small quant.i.ty of ammonia be now introduced into the tube, the sulphide of a.r.s.enic is dissolved, and may thus be readily distinguished from sulphur, which perhaps may have separated.

[Ill.u.s.tration:

_a_, Flask containing the suspected fluid, dilute sulphuric acid and zinc.

_b_, Small tube, at the one end having an almost capillary orifice, where the gas is inflamed.

_c_, Spirit-lamp.

_d_, Support.]

_Reduction Test._ A small quant.i.ty of the suspected sample, in the state of powder, is mixed with twice its weight, or more, of some reducing agent or flux, and the mixture is placed at the bottom of a very small gla.s.s tube, and heated in the flame of a spirit lamp for some time, when the a.r.s.enic gradually sublimes, and condenses in the cooler portion of the tube, under the form of a metallic crust, mirror, or ring. A common test-tube, if of very small diameter, may be employed; but those known as the reduction tubes of Liebig, Rose, or Berzelius are undoubtedly the most convenient and efficient. (See _engr._)

Liebig's method is by using a mixture of equal parts of dry carbonate of sodium and cyanide of pota.s.sium. The suspected substance, perfectly dry and in powder, being first introduced into a Berzelius' tube, is then covered with 6 times the quant.i.ty of this mixture, and so that the whole will not more than half fill the bulb. A very gentle heat is next applied, to expel any adhering moisture from the powder and the tube, after which a strong heat is applied to the bulb, and continued for some time, to effect the entire reduction and sublimation of the a.r.s.enical compound.

[Ill.u.s.tration:

_a_, The a.r.s.enical mixture.

_b_, a.r.s.enical ring.]

The best fluxes to use are ferrocyanide of pota.s.sium dried at 212 F., calcined bitartrate of pota.s.sium, cyanide of pota.s.sium, and powdered charcoal.

The metallic ring is proved to be a.r.s.enical by the properties and tests previously noticed. Should it be imperfectly formed, or masked by decomposed organic matter, the portion of the tube which contains it may be cut off with a file, next coa.r.s.ely powdered, then reintroduced into another a.r.s.enic tube, and the exposure to heat repeated.

The characteristics most simple and well-marked are--

The volatility of the deposit when heated, shown by its escaping from the hotter portion of the tube and condensing on the cooler part higher up or further on.

Its conversion into minute octahedral crystals of a.r.s.enious anhydride, when repeatedly chased up and down the tube by the cautious application of the flame of a spirit lamp first to one part, and then to another. The character of these crystals with respect to volatility, l.u.s.tre, transparency, and form, is so exceedingly well marked that a practised eye may safely identify them, though their weight should not exceed the 1/100th or even the 1/250th part of a grain. A pocket lens is here serviceable. The form of the crystals is very evident with a microscope of 4 powers. Oxide of antimony never forms octahedrons, but only prisms.

In employing this test, particular care must be taken to avoid soiling the sides of the tube in inserting the mixture, and that the substances operated on are perfectly dry; as unless this is attended to, the experiment does not succeed. The common plan is to introduce the mixture through a small paper funnel or tube extemporised for the purpose. The heat at first should be gentle, and merely sufficient to expel any adhering moisture from the mixture and the inner surface of the tube; after which (except where otherwise ordered) the upper portion of the mixture should be strongly heated, and then the bulb or bottom of the tube exposed to the full flame. After the operation is complete the bulb or lower portion of the tube is usually removed by a file, and the portion containing the deposit hermetically sealed, when it may be preserved, unaltered, for any length of time, ready to be produced as evidence if required.

This test is usually regarded as decisive; as we here actually obtain the a.r.s.enic in a solid form, recognisable by the most unequivocal characters.

_Reinsch's Test; Cupro-a.r.s.enical Test._ The suspected solution is strongly acidulated with hydrochloric acid (1 to 6 or 8), and after being raised to ebullition in a porcelain or gla.s.s vessel, a piece of bright and clean metallic copper about 1/2 inch long and 1/4 inch wide in the form of gauze or foil, but preferably the first, is added, and the whole boiled together. The time required for the ebullition varies according to the strength of the solution; when weak it should be continued for at least a quarter of an hour. When the quant.i.ty of a.r.s.enic in the suspected liquid is very small, at least half an hour should elapse before the removal of the copper. In solutions containing a notable quant.i.ty of a.r.s.enic, a few seconds is often sufficient to obtain a coating; but which, for safety sake, may be extended to two or three minutes, or even longer. Liquids rich in organic matter also require longer boiling than those nearly free from it. The coated copper, which has now acquired a characteristic iron-grey colour, is then taken from the liquid, carefully washed in distilled water, in alcohol, and (if greasy) in ether, next dried on blotting-paper, and then either cut into small pieces, or rolled into a small coil or cylinder. It is then heated in a reduction-tube over a spirit lamp, when the metallic a.r.s.enic forming the coating is volatilised, and yields a sublimate of minute octahedral crystals of a.r.s.enious anhydride; or, if the tube be very small, or any reducing agent be added, a bright metallic ring. When the coating on the copper is sufficiently thick, it may be sc.r.a.ped off with a knife, and heated separately in an a.r.s.enic-tube.

This test is invaluable as affording a certain and ready means of abstracting a.r.s.enic from its solution, whether pure or mixed with organic matter. The contents of the stomach or other viscera may thus be at once examined, without any tedious preliminary operations. In this way Dr Christison discovered the presence of a.r.s.enic upwards of four months after interment; and we have ourselves found it two years and eight months after interment. The coated copper may be preserved unharmed for years. Dr Taylor found that the 1-8th of an inch in one of these deposits that had been kept in paper nearly fourteen years gave a well-marked ring of octahedral crystals when heated.

[Ill.u.s.tration]

_Sulphuretted Hydrogen Test; Sulphur Test._ This produces a bright yellow precipitate of trisulphide of a.r.s.enic (orpiment) in solutions containing a free acid; but acts slowly and imperfectly on pure and neutral solutions, and does not disturb those that possess an alkaline reaction. The suspected liquid should therefore be slightly acidulated with hydrochloric or acetic acid before applying this test, unless it be already acid, when it is better first to neutralise it with an alkali, and then to add the acid. The transmission of the gas through the liquid (see _engr._) should be continued for at least half an hour; when the end of the conducting tube, after being well rinsed in the liquid, is removed, and the gla.s.s, lightly covered with a piece of porous paper, set aside in a temperature of about 100 Fahr., until the odour of sulphuretted hydrogen is completely lost. The precipitate is now collected on a small filter, washed with pure water, and dried by a gentle heat. It is then placed in a watch-gla.s.s or small capsule, and redissolved in a little liquor of ammonia, which is then again expelled by heat; or it may be at once submitted to confirmatory tests. It is shown to contain a.r.s.enic by its ready and perfect solubility in ammonia, and in solutions of the fixed alkalies, their carbonates and bicarbonates, and in alkaline sulphides; by being nearly insoluble in hydrochloric acid, even when concentrated and boiling; and by yielding a metallic mirror when mixed with a flux and submitted to the reduction-test (which _see_).

Sulphuretted-hydrogen water and sulphydrate of ammonium act in a similar way to gaseous sulphuretted hydrogen; but much less effectively.

[Ill.u.s.tration]

For accuracy, the sulphuretted hydrogen should be washed by pa.s.sing it through a small bottle containing a little pure water, or dilute sulphuric acid, before allowing it to enter the a.r.s.enical liquor. The reduction of the newly precipitated sulphide is generally regarded as the most important part of the investigation, and requires great care and attention. An extremely elegant and sensitive method of effecting this is by heating the mixture in a stream of dry carbonic acid gas. This method has been followed by Drs Babo and Fresenius with the most satisfactory results, and is thus performed:--(_A_) is a capacious flask for the evolution of carbonic acid, half filled with rather large pieces of solid limestone or marble (not chalk). To one aperture of the doubly perforated cork, a funnel-tube (_a_) is adapted, which nearly reaches to the bottom of the vessel; to the other aperture a tube (_b_), by means of which the gas evolved is conducted into a flask of smaller size (_B_), in which it is washed and dried by concentrated sulphuric acid. The tube (_c_) conducts the carbonic acid into the reduction-tube (_C_), which is shortened in the _engr._, and must be made of difficultly fusible gla.s.s.

When the apparatus is prepared, the sulphide of a.r.s.enic intended for reduction is rubbed in a small basin, previously heated in a water-bath, with about twelve parts of a well-dried mixture consisting of 3 parts of dry carbonate of sodium and 1 part of cyanide of pota.s.sium (prepared by Liebig's method). The mixed powder is then placed on a small strip of card-paper beat into the shape of a gutter, which is next pushed into the reduction-tube up to the point (_f_), and the tube is turned half round.

In this manner the mixture is deposited without soiling any other part of the tube; after which the strip of card-paper is cautiously withdrawn.

The reduction-tube is then, by means of the cork (_e_), fixed in its place; a moderate stream of carbonic acid gas is evolved by pouring hydrochloric acid into the funnel-tube (_a_), and the mixture carefully dried, by very moderately heating the tube along its whole length, by means of a small spirit lamp. When the gas-stream has become so low that the bubbles pa.s.s through the sulphuric acid at intervals of about a second, the spot (_k_) is heated to redness by means of a spirit lamp.

When this point is attained another strong spirit-flame is applied to the mixture, progressing from (_d_) to (_f_), until all the a.r.s.enic is reduced and volatilised (the first flame at the same time continuing in action at (_k_)).

The reduced a.r.s.enic recondenses at the spot (_g_), forming a mirror, whilst an exceedingly small portion escapes at the capillary orifice (_h_), and fills the air with its garlic-like odour. The second spirit lamp is at last slowly advanced towards the other lamp, or the spot (_k_), so as to drive towards (_g_) all the a.r.s.enic which has adhered to the walls of the wider part of the tube. Both lamps are then removed, the tube closed at the point (_h_) by fusion, and heat applied, progressing from the point (_h_) towards (_g_), to contract the mirror on that side also, which increases its beauty and distinctness. The tube is then cut off at (_f_), and hermetically closed and sealed. In this state it becomes a permanent evidence which may be referred to in any future proceedings.

Neither sulphide of antimony nor any other compound of antimony yields a metallic mirror or ring when treated in this way. Less than 1/300 gr. of trisulphide of a.r.s.enic thus gives a very distinct and beautiful mirror; and even 1/500 gr. a clearly perceptible one.

_Voltaic Test._ The wires from the opposite poles of a voltaic battery are immersed or brought in contact with a little of the a.r.s.enious solution placed in a capsule or on a piece of window gla.s.s. If a.r.s.enic be present it is developed at the negative pole; and if this be formed of copper wire, it becomes whitened and a.s.sumes the appearance of polished steel or silver, in consequence of the formation of a.r.s.enide of copper.

_Detection of a.r.s.enic in Organic Mixtures._ Of the tests those which act by producing coloured precipitates are only applicable, with any degree of certainty, to perfectly limpid and colourless liquors. Those depending on the extrication of a.r.s.eniuretted hydrogen are partially free from this inconvenience; but even here, if the suspected liquid be more than slightly charged with organic matter, so much frothing ensues, as to render the process nearly unmanageable. In this respect Reinsch's Test possesses advantages over all others, as it may be applied even to coloured liquids containing a considerable quant.i.ty of organic matter, without these being subjected to any preliminary process, and without danger of failure. In some cases also, as with liquids possessing only a slight degree of consistency or colour, the a.r.s.enic may be separated, after simple filtration and acidulation with hydrochloric acid, by a stream of sulphuretted hydrogen, in the usual manner. The reduction-test is only applicable to solid a.r.s.enious acid, or to compounds of a.r.s.enic obtained by means of other tests or processes. In toxicological examinations the poison is almost always to be sought for in mixtures loaded with organic matter, and under other conditions even more embarra.s.sing. Soon after a.r.s.enic is swallowed it enters the circulation, contaminates the various tissues, localises itself in certain viscera, and is eliminated in the excretions. Hence it becomes necessary not only to examine the solids and liquids in which it is suspected the poison has been administered, the vomited matter, and the contents of the stomach and primae viae, but also, in fatal cases, the stomach itself, the liver, blood, muscles, and more especially the urine.[80] In such cases the stomach is the part first laid open, and a careful examination is made of its contents and coats in order to detect any undissolved particles of the poison, a pocket lens being employed, if necessary, in the search. If any particles, however minute, are found they are carefully collected and submitted to the reduction-test. If the reverse be the case, the stomach (cut into small pieces), together with its contents, is submitted to some further process, to obtain a solution suitable for the application of the usual tests. The liver, also some muscle, and any other portion of the body that may be selected, are likewise separately treated in the same manner. We have here both solid and liquid organic matter to operate on, and the problem for solution is the abstraction of their a.r.s.enic in the simplest and most certain manner, and in a form in which its presence may be demonstrated by tests. This subject has long engaged the attention of the most eminent chemists and toxicologists, and various plans have been proposed for the purpose, among which the following appear to be the most valuable and that usually adopted:--

[Footnote 80: Absorbed a.r.s.enic more particularly localises itself in the liver, in which it may generally be found in from 12 to 15 hours after administration. The liver also generally retains traces of a.r.s.enic long after it has been eliminated from the other viscera and the muscular tissues.]

(Reinsch.) Solids (as the stomach, liver, &c.) are cut into small fragments and boiled in a gla.s.s vessel with water acidulated with about 1-4th of its volume of hydrochloric acid, until the tissues or fragments are entirely broken down into flakes or grains, when the whole, after filtration, is again heated to the boiling-point, and tested as described under Reinsch's test (see ANTIMONY). Liquids do not require this preparation.

Reinsch's test is inapplicable when, as sometimes happens, the a.r.s.enic sought after may be in the state of one of the sulphides--either as orpiment or realgar--a not improbable contingency, when it is remembered that, although a.r.s.enious anhydride or white a.r.s.enic is the form most generally used for criminal or suicidal purposes, the yellow and the red varieties being largely employed in workshops where fireworks are manufactured, have not unfrequently been had recourse to. Again, when the examination of a corpse long buried and disinterred takes place, it must be borne in mind that the a.r.s.enious anhydride taken by the deceased has, by the decomposition of the body, become converted into sulphide. In these cases the hydrochloric acid necessary for the performance of Reinsch's test fails to effect the solution of the sulphide.

Mr Blyth says: "It is found that the post-mortem change into orpiment is never quite complete, so that for the detection of a.r.s.enic in solid organic substances, such as the tissues of the body, the best general method is most decidedly to convert the a.r.s.enic, if present, into the volatile chloride; and according to Dr Taylor, there is always sufficient a.r.s.enic (if present at all) unchanged into sulphide to ensure success. The only necessary caution is that the substance be thoroughly dried, and that the reagents be pure. After drying it is placed in a retort with fuming hydrochloric acid, and slowly distilled by the heat of a sand-bath. The distillate contains chloride of a.r.s.enic (if a.r.s.enic was present), and may be submitted to further tests."

_Estim._ This may be effected in various ways:--

1. GRAVIMETRICALLY:--a.r.s.enic is usually WEIGHED under the form of a.r.s.enate of lead, a.r.s.enate of sesquioxide of iron, tersulphide of a.r.s.enic, (metallic) a.r.s.enic, or (directly) as a.r.s.enious anhydride. The last three only, as the more simple and convenient, will be noticed here:--

As trisulphide:--The whole of the a.r.s.enic being precipitated by a stream of sulphuretted hydrogen, with the necessary precautions, in the manner already noticed, the precipitate, after being carefully collected, washed, and dried, is purified by redissolving it in pure ammonia water, and evaporating the resulting solution in a weighed watch gla.s.s or capsule by the heat of a water-bath. It is then dried at a temperature not above 212 Fahr., and finally weighed. Each grain of the tersulphide so found corresponds to 80487 gr. of a.r.s.enious acid, or 61 gr. of metallic a.r.s.enic.

As (metallic) a.r.s.enic:--Obtained by one of the processes already given.

Each gr. represents 132 gr. a.r.s.enious acid.

As a.r.s.enious anhydride:--Obtained in a weighed capsule or tube, either by the crystallisation or sublimation test. The weight is the answer sought for a.r.s.enious anhydride. Each gr. of this is equiv. to 75758 gr. of metallic a.r.s.enic.

VOLUMETRICALLY. (Method of F. Mohr.) This depends on the fact that an aqueous solution of a.r.s.enious acid, or of an alkaline a.r.s.enite, when mixed with an excess of saturated solution of pure bicarbonate of soda and a little starch-paste, has its a.r.s.enious acid converted into a.r.s.enic acid by a solution of iodine. A standard solution of iodine is, therefore, an appropriate a.r.s.enim'eter for the above mixture. The solution of iodine is added until the blue starch-reaction just begins to appear, the a.r.s.enious solution having been previously exactly neutralised with pure carbonate of soda if acid, or with pure hydrochloric acid if alkaline. The results are accurate when no substance capable of oxidising or decomposing iodine is present in the liquid tested.

_Phys. eff., &c._ a.r.s.enious anhydride or white a.r.s.enic is alike destructive to vegetable and animal life. Seeds soaked in any but a very weak solution of it lose their power of germination, and buds plunged in it become incapable of expanding into flowers. When applied to the leaves, roots, or stems, absorption takes place, and the plant soon perishes. On combustion it evolves the characteristic garlic-like odour of a.r.s.enic, and a.r.s.enic may be discovered in its substance by chemical tests. According to Jager, Gilgenkrantz, and Pereira, a few of the lower order of the algae are occasionally developed in solutions of a.r.s.enious acid. To all animals, from the infusoria up to man, a.r.s.enic proves deleterious, although in different degrees, the highest susceptibility of its effects existing in man on account of the superiority of his development. In all of them death is preceded by inordinate actions and increased evacuations, especially from the mucous surfaces. Difficult respiration, thirst, vomiting, and convulsions are the leading symptoms which gradually develope themselves as we approach the higher grades of the system. (Jager.) In very small or therapeutical doses, properly administered, it is a valuable medicine, and acts as a tonic, alterative, and antispasmodic attenuant, and externally as an escharotic. In slightly increased medicinal doses, or long-continued small doses, nausea, vomiting, purging, griping, debility, emaciation, and all the effects of slow-poisoning, occur in succession--a gradual sinking of the powers of life, without any violent symptom; a nameless feeling of illness, failure of the strength, an aversion to food and drink, and to all the enjoyments of life. Redness of the conjunctiva and eyelids, headache and giddiness, spasms, eczematous eruptions, numbness and paralysis of the limbs, and ptyalism, are also frequent and well-marked symptoms of slow poisoning by a.r.s.enic. In an excessive or poisonous dose the symptoms are rapid and violent, usually indicating extreme gastro-intestinal inflammation and disorder of the cerebro-spinal system, and often occasioning death in from one to three days. The smallest fatal dose found recorded by Christison is 4-1/2 gr., taken in solution. The subject was a child 4 years old, and death occurred in six hours. 2-1/2 gr. destroyed a robust girl in 36 hours. (Letheby.) 2 gr., in solution, are suspected to have caused the death of a full-grown woman. 2 or 3 gr.

may be a fatal dose. (Dr A. Taylor.) Notwithstanding these facts much larger quant.i.ties have been taken, under peculiar circ.u.mstances, with comparative impunity; and cases are not wanting in which even enormous quant.i.ties have produced very trifling effects.

_The dose for animals is_--CATTLE, 5 to 10 grains. HORSE, 5 to 10 grains.

SHEEP, 1 to 2 grains. PIG, 1/2 to 2 grains. DOG, 1/15th to 1/10th of a grain.

Under all circ.u.mstances a.r.s.enious anhydride is, undoubtedly, one of the most powerful of the mineral poisons; and in whatever form or way it is introduced into the system it exerts the same deleterious influence. In all cases, in sufficient doses, its action is to increase the secretions, diminish the contractility of the voluntary muscles, and to produce convulsions, prostration and death.

a.r.s.enic is a non-acc.u.mulative, irritant poison, and exerts no decided chemical or corrosive action on the tissues. (Taylor.)

_Pois., &c.--Symp._ These sometimes begin to appear within half an hour after the poison has been taken, or even sooner; but much more generally, not until after the lapse of some hours. They usually commence with nausea and distress at the stomach, followed by thirst, often intense, and a sense of burning heat in the bowels; then come on constriction of the sophagus, violent vomiting, severe colic pains, tenesmus, and excessive and painful purging, the stools being occasionally b.l.o.o.d.y; but pain, vomiting, &c., do not invariably occur. The pulse is generally quick, small, feeble, and irregular--sometimes scarcely perceptible, and the heart's action is irregular and tumultuous. The tongue is dry and furred; the respiration difficult and panting; the urino-genital apparatus is often affected; there is pain and difficult micturition, and sometimes entire suppression of urine; faintings, coldness of the limbs, and cold sweats, with other signs of debility, intervene. Itching, and eczematous eruptions of the skin, trembling, painful cramps, and contractions of the extremities, and violent convulsions often follow; and after these, a greater or less prostration of strength, which induces a deceitful calm.

At length the heart's action abates, the skin becomes suffused with a cold clammy sweat, and the sufferer dies from exhaustion. The progress, succession, and precise character of the symptoms are modified by the idiosyncrasy of the individual, the quant.i.ty of the poison, and the manner in which it has been taken; and are seldom all present in the same person.

_Treatm._ If vomiting has commenced it should be promoted by tickling the throat, and administering a large quant.i.ty of gelatinous hydrated peroxide of iron, or other appropriate antidote, in divided doses, mixed with a large quant.i.ty of warm or tepid water, strongly sweetened with sugar. If vomiting has not commenced, which is rare, it must be excited by administering 15 to 20 gr. of sulphate of zinc, or ipecacuanha (or in the absence of these, a teaspoonful of flour of mustard) in a tumbler of tepid water, and tickling the throat as before. If these means fail in rapidly inducing copious vomiting, the dose must be repeated, or the stomach-pump had recourse to. Altogether as much as 16 to 18 _oz._ of the hydrated peroxide of iron may be administered. If the poison has been swallowed several hours previously, and hence may have pa.s.sed the pylorus, a strong dose of castor oil or a purgative clyster may be administered, and, after its action, another clyster containing the antidote. As soon as the stomach and bowels are cleared, diuretics and sudorifics should be given in abundance. Lastly, any remaining irritation must be relieved by demulcent and soothing remedies; or if urgent, by slight general or local bleeding, which cannot be earlier practised without danger; and opium, camphor, and ether, followed by tonics, may be had recourse to, to recruit the system.

_Lesions._ Redness and inflammation of the whole primae viae; and sometimes of the mouth, fauces, and sophagus, but more usually the contrary.

Sometimes also, though seldom, there is no marked appearance of inflammation in the stomach and intestines. The stomach is usually highly injected, and frequently marked with extravasations; lungs gorged with blood; mucous lining of trachea reddened; heart generally flabby, and exhibiting deep red or blackish stains, and the right cavities more or less loaded with blood; the conjunctiva is sometimes very vascular; and redness, extravasation of blood, and effusion of serum is occasionally seen in the brain. The blood is frequently, though not invariably, fluid after death, and dark coloured. Under certain circ.u.mstances, the mucous membrane of the stomach and intestines is lined with a mult.i.tude of brilliant points or grains, which have been mistaken for a.r.s.enious anhydride; but which, according to Orfila, are composed of fat and alb.u.men. Placed on burning coals, they decrepitate on drying, and produce a species of explosion or detonation. These grains are also met with in the stomach of persons who have not been poisoned. Digested in water, the liquid obtained from them does _not_ show the presence of a.r.s.enic when submitted to reagents.

_Ant._ In the order of their a.s.sumed efficiency:--MOIST PEROXIDE OF IRON.--See under the preparations of IRON (a.r.s.enici Antidotum, G.).