Chapter XLV: Part IX: Inorganic Poisons (3)

With regard to the preliminary treatment of the stomach and fluids submitted to the analyst, the careful noting of appearances, the decantation, washing, and examination[773] (microscopical and chemical) of any deposit, are precautions so obviously dictated by common sense, that they need only be alluded to in passing. Of some considerable moment is the question which may be put to the analyst in court, in reference to the possible entrance of arsenic into the living body, by accidental and, so to speak, _subtle_ means. Such are the inhaling of the fumes from the burning of arsenical candles,[774] and of emanations from papers (see p. 541),[775] as well as the possible entrance of arsenic into the body after death from various sources, such as arsenical earth, &c.[776]

[773] From some observations of Fresenius in a recent number of the _Zeitschrift f. anal. Chem._, it would seem necessary to test all glass vessels used; for it is difficult at present to purchase arsenic-free glass.

[774] See a case of poisoning (non-fatal) of a lady by the use of arsenical candles, _Med. Times and Gazette_, vol. iii., 1876, p. 367.

[775] To solve this question, it has been at times considered necessary to analyse an extraordinary number of things. In the “affaire Danval” (_Journ. d’Hygiène_, 2e sér., No. 108, July 1878), more than sixty different articles, comprising drugs, drinks, perfumes, bed-curtains, wall-paper, and other matters, were submitted to the experts.

[776] The following important case is related by Sonnenschein:--

Nicholas Nobel and his wife, Jerome, were buried two metres from each other in the churchyard at Spinal, the earth of which notoriously contained arsenic. A suspicion of poisoning arose. The bodies were exhumed, and arsenic was found in the stomach and intestines of Nobel, but not the slightest trace in the corpse of the wife. The remains of the bodies were reinterred, and after six months, on a fresh suspicion of poisoning arising, again exhumed. The corpse of the woman had been put naked in the moist earth during a heavy shower, but this time also no arsenic was detected in it.

§ 741. =Imbibition of Arsenic after Death.=--The arguments which are likely to be used, in favour of a corpse having become arsenical may be gathered from a case related by Sonnenschein:--Certain bodies were exhumed in two churchyards; the evidence went to show that they had been poisoned by arsenic, and this substance was actually found in the bodies, while at the same time it was discovered to exist also in traces in the earth of the churchyard. The theory for the defence was, that although the arsenic in the earth was in an insoluble state, yet that it might combine with lime as an arsenite of lime; this arsenite would become soluble by the action of carbonic acid set free by vegetation, and filter down to the corpse. Sonnenschein suspended a quantity of this earth in water, and passed CO₂ through it for twelve hours; on filtering, the liquid gave no evidence of arsenic. A similar result was obtained when an artificial mixture of 1 grm. of arsenious acid and 1 pound of earth were submitted to the same process.

The fact would appear to stand thus: oxide of iron in ordinary earth retains arsenic, and requires treatment with a concentrated acid to dissolve it. It therefore follows that, if a defence of arsenical earth is likely to be set up, and the analyst finds that by mere extraction of the tissues by _water_ he can detect arsenic, the defence is in all probability unsound. The expert should, of course, deal with this question on its merits, and without prejudice. According to Eulenberg,[777] in arsenical earth--if, after having been crushed and washed, it lies for some time exposed to the disintegrating action of the air--soluble arsenical salts are formed, which may find their way into brooks and supplies of drinking water. We may infer that it is hardly probable (except under very peculiar circumstances) for a corpse to be contaminated internally with an estimable quantity of arsenic from the traces of arsenic met with in a few churchyards.

[777] _Gewerbe Hygiene_, p. 234.

It occasionally happens that an exhumation is ordered a very long time after death, when no organs or parts (save the bones) are to be distinguished. In the case of a man long dead, the widow confessing that she had administered poison, the bones were analysed by Sonnenschein, and a small quantity of arsenic found. Conièrbe and Orfila have both asserted that arsenic is a normal constituent of the bones--a statement which has been repeatedly disproved. Sonnenschein relates:[778]--“I procured from a churchyard of this place (Berlin) the remnants of the body of a person killed twenty-five years previously, and investigated several others in a similar way, without finding the least trace of arsenic. Similar experiments in great number were repeated in my laboratory, but in no case was arsenic recognised.” The opinion of the expert, should he find arsenic in the bones, must be formed from the amount discovered, and other circumstances.

[778] _Gerichtl. Chem._, p. 212.

A difficult case on which to form an opinion is one recorded by William P. Mason,[779] as follows:--

[779] _Chem. News_, Feb. 23, 1894.

The deceased, a farmer, bachelor, sixty-five years of age, and in
good health, was taken violently sick shortly after breakfast, with
vomiting and distress in the stomach. Although a physician was
summoned, the symptoms increased in severity, and a little after
midnight death ensued. The funeral took place three days later.
Certain very damaging pieces of circumstantial evidence having been
collected, the housekeeper was arrested on the charge of murder, it
having been shown, among other things, that on the day preceding the
death she had purchased an ounce of white arsenic.

Thirty-five days after death (from March 20 to April 25) the body
was exhumed, and found in a state of remarkable preservation, and
free from cadaveric smell. The stomach presented evidences of
inflammation.

Portions sent for analysis were the stomach, portion of intestine,
portion of liver, one kidney, and the heart. Arsenic was found in
all these parts. White octahedral crystals were found in the
contents of the stomach, which on separation gave arsenical
reaction.

The arsenic found was:--

Stomach and intestine, 0·2376 grm.
Liver and kidney, 0·0032 „
Heart, 0·0007 „
------
Total as metallic arsenic, 0·2415 „

The amount of arsenic recovered and produced in court was in
quantity sufficient to produce death. Some time after the analytical
report was made to the coroner, it was learned that an embalming
fluid, highly arsenical in character, had been used upon the body by
the undertaker at the time of preparation for burial. No injection
of this embalming fluid was practised, but cloths wrung out in the
fluid were laid upon the face and chest, and were kept constantly
wet therewith during a period of many hours. In all about two quarts
of embalming fluid were so used. Its composition appeared to be a
strongly acidified solution of sodium arsenite and zinc sulphate.
Only the arsenic and zinc were determined quantitatively, and they
were found to be, zinc (metallic), 1·978 per cent., and arsenic
(metallic), 1·365 per cent. by weight. An amount of this fluid
measuring 15·7 c.c. would thus contain a weight of arsenic equal to
that actually recovered from the body.

Extended medical testimony was offered by the prosecution, tending
to show that, under the given circumstances, no fluid of any kind
could have reached the stomach through the nose or mouth after
death, thus anticipating what the defence afterwards claimed, that
the undertaker was responsible for the arsenic discovered in the
remains.

In order to gather further light upon the possibility of cadaveric
imbibition of embalming fluid through the unbroken skin, test was
made for zinc in the heart and stomach, and distinct traces of the
metal were found in each instance. That at least a portion of the
arsenic found in the body was due to _post-mortem_ causes was thus
distinctly proven. A weighed portion (62 grms.) of the stomach and
contents was then most carefully analysed quantitatively for both
zinc and arsenic with the following results:--Arsenic, 0·0648 grm.,
and zinc, 0·0079 grm. Bearing in mind the relative quantities of the
two metals in the embalming fluid, it will be seen that the arsenic
found in the 62 grms. of the stomach was nearly twelve times larger
than it should have been to have balanced the zinc which was also
present. This fact, together with the discovery of crystals of white
arsenic in the stomach, constituted the case for the prosecution, so
far as the chemical evidence was concerned.

The defence made an unsuccessful effort to show that the crystals of
the tri-oxide originated from the spontaneous evaporation of the
embalming fluid. The prosecution met this point by proving that such
fluid had been abundantly experimented upon by exposure to a very
low temperature during an interval of several months, and also by
spontaneous evaporation with a view of testing that very question,
and that the results had in every case been negative. Special
importance was given these experiments, because of the well-known
separation of octahedral crystals during the spontaneous evaporation
of a hydrochloric acid solution of the white oxide, it having also
appeared that, in the manufacture of the embalming fluid, the
arsenic was used as white arsenic.

A very strong point was finally raised for the defence by the
inability of the expert on the side of the prosecution to state
positively whether or not an embalming fluid of the above
composition would diffuse as a whole through dead tissue, or its
several parts would be imbibed at different rates of speed, the zinc
portion becoming arrested by albuminoid material and being therefore
outstripped by the arsenic, or _vice versa_. The prisoner was
ultimately acquitted.

In a case which occurred in the Western States of America, there was good reason for believing that arsenic had been introduced into the corpse of a man _after_ his decease. With regard to the imbibition of arsenic thus introduced, Orfila[780] says:--“I have often introduced into the stomach (as well as the rectum) of the corpses of men and dogs 2 to 3 grms. of arsenious acid, dissolved in from 400 to 500 grms. of water, and have examined the different viscera at the end of eight, ten, or twenty days. Constantly I have recognised the effects of cadaveric imbibition. Sections of the liver or other organs which touch the digestive canal, carefully cut and analysed, furnished arsenic, which could not be obtained sensibly (or not at all) from sections which had not been in contact with this canal. If the corpse remained long on the back after arsenious acid had been introduced into the stomach, I could obtain this metal from the left half of the diaphragm and from the inferior lobe of the left lung, whilst I did not obtain it from other portions of the diaphragm nor from the right lung.” Dr. Reece has also made some experiments on the imbibition of arsenic after death. He injected solutions of arsenious acid into the stomach of various warm-blooded animals, and found at various periods arsenic, not alone in the intestinal canal, but also in the spleen, liver, and kidneys.

[780] _Op. cit._, t. i. p. 309.

§ 742. =Analysis of Wall-Paper for Arsenic.=--The separation of arsenic from paper admits of great variety of manipulation. A quick special method is as follows:--The paper is saturated with chlorate of potash solution, dried, set on fire in a suitable plate, and instantly covered with a bell-glass. The ash is collected, pulverised, and exhausted with cold water, which has previously thoroughly cleansed the plate and bell-glass; the arsenic in combination with the potash is dissolved, whilst oxides of chromium, copper, aluminium, tin, and lead remain in the insoluble portion.[781]

[781] Kapferschlaeger: _Rev. Universelle des Mines_, 1876.

Fresenius and Hintz[782] have elaborated a method for the examination of wall-papers, fabrics, yarns, and similar substances, which, provided the reagents are pure, is accurate and easy. Twenty-five grms. of the substance are placed in a half-litre distilling flask or retort, and 250 c.c. of HCl, specific gravity 1·19, added; after digestion for an hour, 5 c.c. of a saturated solution of ferrous chloride are added, and the liquid slowly distilled until frothing stops any farther distillation. A further quantity of 100 c.c. HCl is then added, and distilled over. The receiver, in each case, contains water, and must be kept cool. The united distillates are diluted to 800 c.c. and saturated with SH₂. The arsenious sulphide is collected on an asbestos filter. After partial washing, it is heated with bromine in HCl of 1·9 specific gravity, and the solution again distilled with ferrous chloride. The distillate, on now being treated with SH₂, gives arsenious sulphide free from organic matter.

[782] _Zeit. anal. Chem._, xxvii. 179-182.

§ 743. =Estimation of Arsenic.=--Most of the methods for the quantitative determination of arsenic are also excellent tests for its presence. It may be regarded, indeed, as an axiom in legal chemistry, that the precise amount of every substance detected, if it can be weighed or estimated by any process whatever, should be accurately stated. Indefinite expressions, such as “a small quantity was found,” “traces were detected,” &c., are most objectionable. The more perfect of the methods of evolving arsenic can be made quantitative. For example, the galvanic process introduced by Bloxam may be utilised as follows:--A fractional part of the arsenical solution is taken for the experiment; the bottom of a narrow-necked bottle of about 100 c.c. capacity is removed, and replaced by a piece of vegetable parchment. The neck of the bottle carries a cork, which is pierced by (1) a platinum wire, which is attached to a platinum electrode; (2) a short tube, bent at right angles, and connected by piping with a longer tube, which has also a rectangular bend, and dips into a solution of silver nitrate; (3) an ordinary funnel-tube, reaching nearly to the bottom. The bottle is placed in a beaker of such a size as to leave a small interval between the two, and the whole apparatus stands in a large vessel of cold water. Dilute sulphuric acid is now put into the bottle, and also into the beaker, so that the fluid reaches exactly the same level in each. The positive platinum electrode of a battery of six of Grove’s cells, or other efficient combination, is immersed in the liquid outside the bottle, connection with the negative plate is established, and hydrogen very soon comes off, and passes over into the nitrate of silver solution. When all the air is expelled, a portion of the rectangular tube is heated to redness, and if there is no stain nor any reduction of the silver, the acid is pure. If the gas is passed for a long time into the silver solution, the silver will be reduced to some extent by the hydrogen, although arsenic-free;[783] so that it is better to rely upon the metallic ring or stain, which is certain to be formed on heating a portion of the tube red-hot, and keeping it at that temperature for _at least ten minutes_. The liquid is then passed through the funnel in successive portions; if arsenic is present, there will be a decided metallic ring on heating the tube as before, and if antimony is present, there will also be a stain; the distinctions between these stains have been described at p. 557.

[783] Nitrate of silver solution is reduced by H₂, CH₃, PH₃, and SbH₃; hence it is absolutely necessary in any qualitative examination to prove that arsenious acid has actually been produced in the silver solution.

The tube is kept red-hot until the stain is very distinct; then the source of heat is removed, and the gas allowed to bubble through the argentic nitrate solution, which it decomposes, as before detailed (p. 526). This process is continued until, on placing the delivery tube in a sample of clear nitrate of silver solution, there is no darkening of colour. In certain cases this may take a long time, but the apparatus, once set to work, requires little superintendence. At the conclusion, the whole of the arsenic is separated,--part is in the silver solution as arsenious acid, part in the tube as a ring of metallic arsenic. The portion of the tube containing the metallic arsenic should be cut off with a file and weighed, the arsenic then removed and re-weighed; the loss is the metal approximately. Or, the weight of the film may be estimated by having a set of similar deposits of known weight or quantities, in tubes exactly corresponding to those used in the analysis, and comparing or matching them.

The arsenious acid in the nitrate of silver may be dealt with in several ways. The equation given (p. 526) shows clearly that pure arsine, passed into nitrate of silver solution, decomposes it in such a manner that, if either the silver deposited or the free acid is estimated, the quantity of arsenic can from such data be deduced. In operating on organic liquids, ammonia and other products may be given off, rendering either of the indirect processes inadvisable. A very convenient method, applicable in many cases, is to throw out the silver by hydrochloric acid, alkalise the filtrate by bicarbonate of soda, and titrate with iodine solution. The latter is made by dissolving exactly 12·7 grms. of pure dry iodine by the aid of 18 grms. of potassic iodide in one litre of water, observing that the solution must take place in the cold, without the application of heat. The principle of the titration is, that arsenious acid, in the presence of water and free alkali, is converted into arsenic acid--

As₂O₃ + 4I + 2Na₂O = As₂O₅ + 4NaI.

The end of the reaction is known by adding a little starch-paste to the solution; as soon as a blue colour appears, the process is finished.

Another convenient way by which (in very dilute solutions of arsenious acid) the arsenic may be determined, is a colorimetric method, which depends on the fact that sulphuretted hydrogen, when arsenious acid is present in small quantity, produces no precipitate at first, but a yellow colour, proportionate to the amount of arsenic present. The silver solution containing arsenious acid is freed from silver by hydrochloric acid; a measured quantity of saturated SH₂ water is added to a fractional and, if necessary, diluted portion, in a Nessler cylinder or colorimetric apparatus, and the colour produced exactly imitated, by the aid of a dilute solution of arsenious acid, added from a burette to a similar quantity of SH₂ water in another cylinder, the fluid being acidified with HCl.

§ 744. =Destruction of the Organic Matter by Nitric Acid, and Subsequent Reduction of the Arsenic Acid to Arsine (Arseniuretted Hydrogen), and final Estimation as Metallic Arsenic.=--This process, which is essentially a combination of several, has been much improved in its details by R. H. Chittenden and H. H. Donaldson.[784] 100 grms. of the suspected matters, cut up into small pieces, are heated in a porcelain dish of suitable size, stirred by means of a glass rod with 23 c.c. of pure concentrated nitric acid, and heated up to from 150° to 160°. When the matters assume a yellow or orange colour, the bath is removed from the source of heat, and 3 c.c. of pure concentrated sulphuric acid added, and the mixture stirred, when the mass becomes brown, swells up, and evolves dense nitrous and other fumes. The vessel is again heated to 180°, and while hot 8 c.c. of pure concentrated nitric acid are added, drop by drop, with continual stirring. After this addition, it is heated to 200° for fifteen minutes, and the result on cooling is a hard carbonaceous residue wholly free from nitric acid. The arsenic is in this way oxidised into arsenic acid, which is easily soluble in water. The contents of the dish are, therefore, perfectly extracted by boiling water, the aqueous extract filtered, and evaporated to dryness. The next process is to obtain the arsenic in a metallic state:--

[784] _American Chem. Journ._, vol. ii., No. 4; _Chem. News_, Jan. 1881, p. 21.

The flask, a Bunsen’s wash-bottle of 200 c.c. capacity, is provided with a small separating funnel of 65 c.c. capacity, with glass stop-cock. This is a very material aid to the obtaining of a slow and even evolution of gas, an important desideratum when all loss is to be avoided; for with only a funnel tube, every time a small portion of fluid is added, a sudden rush of gas takes place, with probably a small, but still more or less appreciable, loss. But the separating funnel, filled with the acid mixture, can be so arranged as to give a constant and regular supply of fluid at the rate of two or three drops per minute, more or less. The gas generated is dried by a calcic chloride tube, and then passes through a tube of hard glass, heated to a red heat by a miniature furnace of three Bunsen lamps with spread burners, so that a continuous flame of 6 inches is obtained, and with a proper length of cooled tube not a trace of arsenic passes by. The glass tube where heated is wound with a strip of wire gauze, both ends being supported upon the edges of the lamp frame, so that the tube does not sink down when heated. The small furnace is provided with two appropriate side pieces of sheet metal, so that a steady flame is always obtained. When the quantity of arsenic is very small, the tube is naturally so placed that the mirror is deposited in the narrow portion; but when the arsenic is present to the extent of 0·005 grm., the tube should be 6 mm. in inner diameter, and so arranged that fully 2 inches of this large tube are between the flame and the narrow portion. When the quantity of arsenic is less, the tube can naturally be smaller.

Acids of different strengths are made as follows:--

Acid No. 1.

545 c.c. pure conc. H₂SO₄.
5000 c.c. H₂O.

Acid No. 2.

109 c.c. pure conc. H₂SO₄.
1640 c.c. Acid No. 1.

Acid No. 3.

218 c.c. pure conc. H₂SO₄.
1640 c.c. Acid No. 1.

Acid No. 4.

530 c.c. pure conc. H₂SO₄.
1248 c.c. H₂O.

25 to 35 grms. of granulated zinc, previously alloyed with a small quantity of platinum, are placed in the generator, and everything being in position, the apparatus is filled with hydrogen by the use of a small quantity of acid No. 2. After a sufficient time has elapsed, the gas is lighted at the jet, and the glass tube heated to a bright redness.

The arsenical solution in concentrated form is mixed with 45 c.c. of acid No. 2, and the mixture passed into the separating funnel, from which it is allowed to flow into the generator at such a rate that the entire fluid is introduced in one hour or one and a half; 40 c.c. of acid No. 3 are then added and allowed to flow slowly into the generator, and, lastly, 45 c.c. of acid No. 4. The amount of time required will vary with the amount of arsenic: 2 to 3 mgrms. of arsenic will require about two to three hours for the entire decomposition, while 4 to 5 mgrms. will need perhaps three to four hours. Where the amount of arsenic is small, only 25 grms. of zinc are needed, and but 45 c.c. of acid No. 2, 30 c.c. of acid No. 3, and 30 c.c. of acid No. 4; but when 4 to 5 mgrms. of arsenic are present, it is better to take the first mentioned quantities of zinc and acids.

The arsenic being thus collected as a large or small mirror of metal, the tube is cut at a safe distance from the mirror, so that a tube of perhaps 2 to 6 grms. weight is obtained. This is carefully weighed, and then the arsenic removed by simple heating; or, if the arsenic is to be saved (as in a toxicological case), dissolved out with strong nitric acid. The tube is then cleaned, dried, and again weighed, the difference giving the weight of metallic arsenic, from which, by a simple calculation, the amount of arsenious oxide can be obtained. Some test results are given as follows; they were obtained by introducing definite quantities of arsenious oxide in the form of a solution mixed with 45 c.c. of No. 2 acid, &c.:--

Quantity of Wt. of Metallic Theoretical Wt. of
Arsenic introduced. Arsenic found. Metallic Arsenic.

0·005 grm. As₂O₃ 0·00373 0·00378
0·005 „ „ 0·00370 0·00378
0·004 „ „ 0·00300 0·00303
0·002 „ „ 0·00151 0·00151

Sanger estimates and tests for minute quantities of arsenic by the Marsh-Berzelius process, and uses a generator of hydrogen; that is to say, the hydrogen is evolved in the ordinary way from zinc and sulphuric acid, and the issuing gas dried by calcic chloride; but into this flask is also delivered from another flask, charged with sulphuric acid and zinc, pure hydrogen, so that into the second flask, little by little, may be added the solution to be tested; and, owing to the generating flask, the gas may be made to give a uniform current, and at the end of the operation all arsine swept out. To estimate the quantities of arsenic in the gas, the reduction tube is heated, and a mirror or mirrors obtained, and compared with a set of standard mirrors. The standard mirrors are made as follows:--One grm. of arsenious oxide, purified by repeated sublimation, is dissolved with the aid of a little sodic bicarbonate, and, after acidification with dilute sulphuric acid, made up to 1 litre. This standard solution contains 1 mgrm. of As₂O₃ in every c.c., and is used to make a second standard solution, containing 0·01 mgrm., to every c.c., by diluting 10 c.c. to a litre. Of this last solution, 1 c.c., 2 c.c., 3 c.c., and so on, are measured and introduced into the reduction flask, and the standard mirrors obtained. It is recommended, for obvious reasons, to make more than one standard for each quantity, for the appearance of the mirrors from the same amount of arsenic varies. The tubes are hermetically sealed, and, when not in use, kept in the dark.

This process is convenient for small amounts of arsenic; but, as stated before, the results are given as metallic arsenic, whereas the films appear never to be composed of pure metallic arsenic, but a mixture of hydride and suboxide. Test experiments give, however, fair results.[785]

[785] _Proc. American Academy of Arts and Sciences_, vol. xxvi.

§ 745. =Arsine Developed from an Alkaline Solution.=--Fleitmann discovered in 1851 that arsenic, mixed with finely divided zinc, and excess of soda or potash added, evolved arsine; but no stibine was evolved under the same conditions. In 1873 J. W. Gatehouse suggested the use of aluminium and sodic hydrate as a modification of Fleitmann’s test, for the purpose of distinguishing between arsenic and antimony; and this is now the usual process adopted. The hydrogen comes off regularly even in the cold, but it is best to apply a little heat. This test will evolve arsine from arsenious acid, and also from arsenic trisulphide; but it is not available for the detection of arsenic, when the arsenic is in the form of arsenic acid. According to Clark,[786] it is not adapted for quantitative purposes, because, owing to the formation of solid hydride, about one-fifth remains behind.

[786] _Journ. Chem. Soc._, 1893, 884.

E. W. Davy, in 1876, proposed the use of sodium amalgam for the generation of arsine; on the whole, it is, however, not so convenient as the aluminium process.

The liquid to be tested is made strongly alkaline with pure sodic or potassic hydrate placed in a flask connected with a tube dipping into a 4 per cent. solution of silver nitrate, a few pieces of sheet aluminium added, and the flask gently heated; any arsine present will reduce the silver. The silver solution thus blackened may be treated in the manner described (p. 567).

§ 746. =Precipitation as Tersulphide.=--Despite the advantages of some of the processes described, which are (to a certain extent) easy and accurate, not a few chemists still prefer the old method of precipitation with hydric sulphide SH₂, because, although tedious, it has stood the test of experience. If this be used, it is well in most cases to pass sulphurous anhydride through the liquid until it smells strongly of the gas, for by this means any arsenic acid present is reduced, the sulphurous anhydride is quickly got rid of by a current of carbonic anhydride, and then the liquid is saturated with hydric sulphide. In the ordinary way, much time is often wasted in saturating the liquid with this gas. Those, however, who have large laboratories, and daily employ hydric sulphide, possess (or should possess) a water saturated with the gas under pressure; such a liquid, added in equal volume to an arsenical solution, is able to convert the whole of the arsenic into sulphide in a very few minutes. Those who do not possess this hydric sulphide water can saturate in an hour the liquid to be tested, by passing the gas in under pressure.[787] A convenient method is to evolve SH₂ from sulphide of antimony and ClH; the gas passes first into a wash-bottle, and then into a strong flask containing the solution under trial. This flask is furnished with a safety-valve, proportioned to the strength of the apparatus; the two tubes dipping into the wash-bottle and the last flask are provided with Bunsen’s valves, which only allow the gas to pass in one direction. The hydric sulphide is then driven over by heat, and when sufficient gas has in this way passed into the liquid, the flame is withdrawn, and the apparatus allowed to stand for some hours, the valves preventing any backward flow of the liquid or gas. When the precipitate has settled to the bottom, the supernatant fluid is carefully passed through a filter, and the precipitate washed by decantation in the flask, without transference to the filter, if it can be avoided.

[787] Hydric sulphide gas has been liquefied, and is now an article of commerce, being sold in iron bottles.

The impure sulphide is washed with water, then with alcohol, then with carbon disulphide, then, after having got rid of the lead, again with alcohol, and finally with water; it is then dissolved in ammonia, the ammonia solution filtered, and the filtrate evaporated to dryness on a sand-bath, at a somewhat high temperature; in this way it is freed from sulphur and, to a great extent, from organic matter; after weighing, it may be purified or identified by some of the following methods:--

(_a_) =Solution in Ammonia and Estimation by Iodine.=[788]--The filter is pierced, the sulphide washed into a flask by ammonia water (which need not be concentrated), and dissolved by warming, filtered from any insoluble matter, and estimated by iodine and starch.

[788] P. Champion and H. Pellett, _Bull. Soc. Chim._ (2), xxvj. pp. 541-544.

(_b_) =Oxidation of the Sulphide and Precipitation as Ammonia Magnesian Arseniate, or Magnesia Pyro-Arseniate.=--The tersulphide, as before, is dissolved in ammonia (not omitting the filter-paper, which should be soaked in this reagent), the solution filtered, and evaporated to dryness. The dry residue is now oxidised by fuming nitric acid, taking care to protect the dish with a large watch-glass (or other cover) during the first violent action; the dish is then heated in the water-bath until all the sulphur has disappeared, and only a small bulk of the liquid remains; it is then diluted and precipitated by “magnesia mixture.”[789] The fluid must stand for several hours, and, if the arsenic is to be determined as the usual ammoniacal salt, it must be passed through a weighed filter, and washed with a little ammoniacal water (1 : 3). The solubility of the precipitate is considerable, and for every 16 c.c. of the filtrate (not the washings) 1 mgrm. must be allowed. The precipitate, dried at 100°, 2(NH₄MgAsO₄)H₂O, represents 39·47 per cent. metallic arsenic.

[789] Magnesia Mixture:--

Sulphate of magnesia, 1
Chloride of ammonium, 1
Solution of ammonia, 4
Water, 8

Dissolve; then allow to stand for several days; finally filter, and keep for use.

The solubility of the magnesium arseniate itself, and the general dislike which chemists have to weighing in such hygroscopic material as a filter, are, perhaps, the main reasons for the variation of this old method, which has lately come into notice. Rose proposed some time ago the conversion of the double salt into the pyro-arseniate--a method condemned by Fresenius and Parnell, but examined and pronounced a practicable and accurate process by Remol, Rammelsberg, Thorpe, Fuller, Wittstein, Emerson, Macivor, Wood, and Brauner. The modification of Rose’s process, recommended by Wood,[790] and still further improved by Brauner,[791] may be accepted.

[790] _Zeitschrift für anal. Chem._, vol. xiv. p. 356.

[791] _Ibid._, xvj. pp. 57, 58.

The precipitation is effected by magnesia mixture, with the addition of half its bulk of alcohol. The solution is allowed to stand for several hours, until it is possible to decant the clear liquid from the precipitate; the latter is now dissolved in ClH, reprecipitated as before, thrown on a small filter, and washed with a mixture of one volume of ammonia, two volumes of alcohol, and three of water.

The precipitate is now dried, and transferred as completely as possible from the filter into a small porcelain crucible, included in a larger one made of platinum, moistened with nitric acid, covered and heated at first gently, lastly to a bright redness; the filter is then treated similarly, and the crucible with its contents weighed. Pyro-arseniate of arsenic (Mg₂As₂O₇) contains 48·29 per cent. of metallic arsenic.

(_c_) =Conversion of the Trisulphide of Arsenic into the Arsenomolybdate of Ammonia.=--The purified sulphide is oxidised by nitric acid, the acid solution is rendered alkaline by ammonia, and then precipitated by a molybdenum solution, made as follows:--100 grms. of molybdic acid are dissolved in 150 c.c. of ordinary ammonia and 80 of water; this solution is poured drop by drop into 500 c.c. of pure nitric acid and 300 c.c. of water; it is allowed to settle, and, if necessary, filtered. The molybdic solution must be mixed in excess with the liquid under treatment, the temperature raised to 70° or 80°, and nitric acid added in excess until a yellow coloration appears; the liquid is then passed through a tared filter, and dried at 100°. It contains 5·1 per cent. of arsenic acid [3·3 As].[792]

[792] Champion and Pellett, _Bull. Soc. Chim._, Jan. 7, 1877.

(_d_) =Conversion of the Sulphide into Metallic Arsenic.=--If there should be any doubt as to the nature of the precipitated substances, the very best way of resolving this doubt is to reduce the sulphide to metal; the easiest method of proving this is to dissolve in potash and obtain arsine by the action of aluminium; or if it is desired to evolve arsine from an acid solution with zinc in the usual way, then by dissolving a slight excess of zinc oxide in potash or soda, and dissolving in this the arsenic sulphide; the zinc combines with all the sulphur, and converts the sulpharsenite into arsenite; the zinc sulphide is filtered off, and the filtrate acidified and introduced into Marsh’s apparatus. The original process of Fresenius was to mix the sulphide with carbonate of soda and cyanide of potassium, and place the mixture in the wide part of a tube of hard German glass, drawn out at one end to a capillary fineness. Carbonic anhydride, properly dried, was passed through the tube, and the portion containing the mixture heated to redness; in this way the arsenical sulphide was reduced, and the metal condensed in the capillary portion, where the smallest quantity could be recognised. A more elaborate and accurate process, based on the same principles, has been advocated by Mohr.[793]

[793] Mohr’s _Toxicologie_, p. 57.

A convenient quantity of carbonate of soda is added to the sulphide, and the whole mixed with a very little water, and gently warmed. The yellow precipitate is very soon dissolved, and then the whole is evaporated carefully, until it is in a granular, somewhat moist, adhesive state. It is now transferred to a glass tube, open at top and bottom, but the top widened into a funnel; this tube is firmly held perpendicularly on a glass plate, and the prepared sulphide hammered into a compact cylinder by the aid of a glass rod, which just fits the tube. The cylinder is now dried over a flame, until no more moisture is to be detected, and then transferred into a glass tube 4 or 5 inches long, and with one end drawn to a point (the weight of this tube should be first accurately taken). The tube is connected with the following series:--(1) A chloride of calcium tube; (2) a small bottle containing nitrate of silver solution; (3) a hydrogen-generating bottle containing zinc and sulphuric acid. The hydrogen goes through the argentic nitrate solution, leaving behind any sulphur and arsenic it may contain; it is then dried by chloride of calcium, and streams in a pure dry state over the cylinder of prepared sulphide (no error with regard to impurities in the gas is likely to occur; but in rigid inquiries it is advisable to heat a portion of the tube, previous to the insertion of the cylinder, for some time, in order to prove the absence of any external arsenical source); when it is certain that pure hydrogen, unmixed with air, is being evolved, the portion of the tube in which the cylinder rests is heated slowly to redness, and the metallic arsenic sublimes at a little distance from the source of heat. Loss is inevitable if the tube is too short, or the stream of hydrogen too powerful.

The tube after the operation is divided, the portion soiled by the soda thoroughly cleansed, and then both parts weighed; the difference between the weight of the empty tube and the tube + arsenic gives the metallic arsenic. This is the process as recommended by Mohr; it may, however, be pointed out that the glass tube itself loses weight when any portion of it is kept red-hot for some little time; and, therefore, unless the crust is required in the original tube, it is better to divide it, carefully weigh the arsenical portion, remove the crust, and then re-weigh. The method is not perfectly accurate. The mirror is not pure metallic arsenic (see p. 571), and if the white alkaline residue be examined, arsenic will be detected in it, the reason being that the arsenical sulphide generally contains pentasulphide of arsenic as well as free sulphur. Now the pentasulphide does not give up metallic arsenic when treated as before detailed; nor, indeed, does the trisulphide, if mixed with much sulphur, yield an arsenical crust. It is, therefore, of great moment to free the precipitate as much as possible from sulphur, before attempting the reduction.

The development of a reducing gas from a special and somewhat complicated apparatus is not absolutely necessary. The whole process of reduction, from beginning to end, may take place in a single tube by any of the following processes:--(1) The sulphide is mixed with oxalate of soda (a salt which contains no water of crystallisation), and the dry mixture is transferred to a suitable tube, sealed at one end. An arsenical mirror is readily obtained, and, if the heat is continued long enough, no arsenic remains behind--an excellent and easy method, in which the reducing gas is carbonic oxide, in an atmosphere of carbonic anhydride. (2) The sulphide is oxidised by _aqua regia_, and the solution evaporated to complete dryness. The residue is then dissolved in a few drops of water, with the addition of some largish grains of good wood charcoal (which absorb most of the solution), and the whole carefully dried. The mass is now transferred to a tube closed at one end, a little charcoal added in the form of an upper layer, and heat applied first to this upper layer, so as to replace the air with CO₂, and then to bring the whole tube gradually to redness from above downwards. In this case also the whole of the arsenic sublimes as a metallic mirror.

There are various other modifications, but the above are trustworthy, and quite sufficient. Brugelmann’s method of determining arsenic, elsewhere described, would appear to possess some advantages, and to promise well; but the writer has had no personal experience of it with regard to arsenic.

§ 747. =Conversion of Arsenic into Arsenious Chloride= (AsCl₃).--This process, first employed by Schneider and Fyfe, and afterwards modified by Taylor, differs from all the preceding, since an attempt is made to separate by one operation volatile metallic chlorides, and to destroy the organic matter, and thus obtain two liquids--one a distillate--tolerably clear and free from solid particles, whilst the mass in the retort retains such metals as copper, and is in every way easy to deal with.

Schneider and Fyfe employed sulphuric acid and common salt; but Taylor recommends hydrochloric acid, which is in every respect preferable. As recommended by Taylor, all matters, organic or otherwise, are to be completely desiccated before their introduction into a retort, and on these dried substances sufficient pure hydrochloric acid poured, and the distillation pushed to dryness. Every one is well aware how tedious is the attempt to dry perfectly the organs of the body (such as liver, &c.) at any temperature low enough to ensure against volatilisation of such a substance as, _e.g._, calomel. This drying has, therefore, been the great stumbling-block which has prevented the general application of the process. It will be found, however, that drying in the ordinary way is by no means necessary. The writer cuts up the solid organ (such as liver, brain, &c.) with scissors into small pieces, and transfers them to a retort fitted by an air-tight joint to a Liebig condenser; the condenser in its turn being connected with a flask by a tube passing through an india-rubber stopper dipping into a little water. Another tube from the same flask is connected with india-rubber piping, which is connected with a water-pump, the fall tube of which terminates in the basement of a house over a gully. The distillation is now carried on to carbonisation; on cooling, a second quantity of hydrochloric acid is added, and the last fraction of the distillate examined for arsenic. If any is found, a third distillation is necessary. At the termination of the operation the retort is washed with water, the solution filtered, and this solution and the distillate are each separately examined for arsenic. If properly performed, however, the second distillation brings over the whole of the arsenical chloride,[794] and none will be found in the retort. With the above arrangement there can be no odour, nor is there any loss of substance. In the distillate the arsenic can hardly be in the form of arsenious chloride, but rather arsenious acid and hydrochloric acid; for the chloride easily splits up in the presence of water into these substances. It is best to convert it into the trisulphide. Taylor[795] recommends evolving arsine in the usual way, and passing the arsine (AsH₃) into solution of silver nitrate, finally estimating it as an arseniate of silver. Objections with regard to the impurity of reagents should be met by blank experiments. Kaiser[796] has proposed and practised a modification of this method, which essentially consists in the use of sulphuric acid and sodic chloride (as in Schneider and Fyfe’s original process), and in passing the distillate first into a flask containing a crystal or two of potassium chlorate, and thence into an absorption bulb; in the latter most of the arsenic is found in the form of arsenic acid, the chloride having been oxidised in its passage. The apparatus is, however, complicated in this way without a corresponding advantage.[797] Lastly, E. Fischer[798] has shown that it is a considerable advantage to add from 10 to 20 c.c. of a saturated solution of ferrous chloride before distilling with HCl. In this way all the arsenic, whether as arsenic or arsenious acids, is easily converted into chloride.

[794] Dragendorff asserts to the contrary; but we may quote the authority of Taylor, who has made several experiments, in which he obtained all the arsenic as chloride. The writer has performed the process many times, each time carefully testing the mass in the retort for arsenic; but the result proved that it had entirely passed over.

[795] _Principles of Medical Jurisprudence_, vol. i. p. 267.

[796] _Zeitschr. f. anal. Chem._, xiv. pp. 250-281.

[797] Selmi (_Atti dell. Accademia dei Lincei_, Fasc. ii., 1879) proposed a modification of Schneider’s process. The substances are treated with hot, pure sulphuric acid, and at the same time the liquid is traversed by a stream of hydrochloric acid gas. The resulting distillate is tested for arsenic by Marsh’s process. Selmi states that, operating in this way, he has detected 1/400 of a mgrm. of As₂O₃ in 100 grms. of animal matter.

[798] _Scheidung u. Bestimmung d. Arsens_; Liebig’s _Annalen d. Chemie_, Bd. ccvii. p. 182.

2. ANTIMONY.

§ 748. =Metallic Antimony.=--Atomic weight, 120·3 (R. Schneider), 120·14 (Cook[799]); specific gravity, 6·715; fusing-point about 621° (1150° F.). In the course of analysis, metallic antimony may be seen as a black powder thrown down from solutions; as a film deposited on copper or platinum; and, lastly, as a ring on the inside of a tube from the decomposition of stibine. At a bright red-heat it is volatilised slowly, even when hydrogen is passed over it; chlorine, bromine, and iodine combine with it directly. It may be boiled in concentrated ClH without solution; but _aqua regia_, sulphides of potassium and sodium readily dissolve it. The distinction between thin films of this metal and of arsenic on copper and glass are pointed out at pp. 557 and 559. It is chiefly used in the arts for purposes of alloy, and enters to a small extent into the composition of fireworks (_vide_ pp. 534 and 581).

[799] _Ann. Phys. Chem._ (2), v. pp. 255-281.

§ 749. =Antimonious Sulphide.=--Sulphide of antimony = 336; composition in 100 parts, Sb 71·76, S 28·24. The commercial article, known under the name of black antimony, is the native sulphide, freed from silicious matter by fusion, and afterwards pulverised. It is a crystalline metallic-looking powder, of a steel-grey colour, and is often much contaminated with iron, lead, copper, and arsenic.

The amorphous sulphide (as obtained by saturating a solution of tartar emetic with SH₂) is an orange-red powder, soluble in potash and in ammonic, sodic, and potassic sulphides; and dissolving also in concentrated hydrochloric acid with evolution of SH₂. It is insoluble in water and dilute acid, scarcely dissolves in carbonate of ammonia, and is quite insoluble in potassic bisulphite. If ignited gently in a stream of carbonic acid gas, the weight remains constant. To render it anhydrous, a heat of 200° is required.

The recognition of arsenic in the commercial sulphide is most easily effected by placing 2 grms. or more in a suitable retort (with condenser), adding hydrochloric acid, and distilling. The chloride of arsenic passes over before the chloride of antimony; and by not raising the heat too high, very little antimony will come over, even if the distillation be carried almost to dryness. The arsenic is detected in the distillate by the ordinary methods.

Several lamentable accidents have happened through mistaking the sulphide of antimony for oxide of manganese, and using it with potassic chlorate for the production of oxygen. The addition of a drop of hydrochloric acid, it is scarcely necessary to say, will distinguish between the two.

Antimony is frequently estimated as sulphide. An amorphous tersulphide of mercury, containing a small admixture of antimonious oxide and sulphide of potassium, is known under the name of _Kermes mineral_, and has lately been employed in the vulcanising of india-rubber. Prepared in this way, the latter may be used for various purposes, and thus become a source of danger. It behoves the analyst, therefore, in searching for antimony, to take special care not to use any india-rubber fittings which might contain the preparation.

A _pentasulphide of antimony_ (from the decomposition of Schleppe’s salt [Na₃Sb₆S₄ + 9H₂O], when heated with an acid) is used in calico-printing.

§ 750. =Tartarated Antimony, Tartrate of Potash and Antimony, or Tartar Emetic=, is, in a medico-legal sense, the most important of the antimonial salts. Its formula is KSbC₄H₄O₇H₂O, and 100 parts, theoretically, should contain 35·2 per cent. of metallic antimony. The B.P. gives a method of estimation of tartar emetic not free from error, and Professor Dunstan has proposed the following:--Dissolve 0·3 grm. of tartar emetic in 80 c.c. of water, add to this 10 c.c. of a 5 per cent. solution of sodium bicarbonate, and immediately titrate with a decinormal solution of iodine, using starch as an indicator. One c.c. of _n_/10 iodine = 0·0166 grm. tartar emetic; therefore, if pure, the quantity used by 0·3 grm. should be 18 c.c. Tartar emetic occurs in commerce in colourless, transparent, rhombic, octahedral crystals, slightly efflorescing in dry air.

A crystal, placed in the subliming cell (p. 258), decrepitates at 193·3° (380° F.), sublimes at 248·8° (480° F.) very slowly and scantily, and chars at a still higher temperature, 287·7° (550° F.). On evaporating a few drops of a solution of tartar emetic, and examining the residue by the microscope, the crystals are either tetrahedra, cubes, or branched figures. 100 parts of cold water dissolve 5 of tartar emetic, whilst the same quantity of boiling water dissolves ten times as much, viz., 50. The watery solution decomposes readily with the formation of algæ; it gives no precipitate with ferrocyanide of potassium, chloride of barium, or nitrate of silver, unless concentrated.

§ 751. =Metantimonic Acid=, so familiar to the practical chemist from its insoluble sodium salt, is technically applied in the painting of glass, porcelain, and enamels; and in an impure condition, as antimony ash, to the glazing of earthenware.

§ 752. =Pharmaceutical, Veterinary, and Quack Preparations of Antimony.=[800]

[800] The history of antimony as a drug is curious. Its use was prohibited in France in 1566, because it was considered poisonous, one Besnier being actually expelled from the faculty for transgressing the law on this point. The edict was repealed in 1650; but in 1668 there was a fresh enactment, confining its use to the doctors of the faculty.

(1) =Pharmaceutical Preparations=:--

=Oxide of Antimony= (Sb₂O₃) is a white powder, fusible at a low red heat, and soluble without effervescence in hydrochloric acid, the solution responding to the ordinary tests for antimony. Arsenic may be present in it as an impurity; the readiest means of detection is to throw small portions at a time on glowing charcoal, when very small quantities of arsenic will, under such conditions, emit the peculiar odour. Carbonate of lime appears also to have been found in the oxide of commerce.

=Antimonial Powder= is composed of one part of oxide of antimony and two parts of phosphate of lime; in other words, it ought to give 33·3 per cent. of Sb₂O₃.

=Tartar Emetic= itself has been already described. The preparations used in medicine are--

=The Wine of Antimony= (=Vinum antimoniale=), which is a solution of tartar emetic in sherry wine, and should contain 2 grains of the salt in each ounce of the wine (0·45 grm. in 100 c.c.).

=Antimony Ointment= (=Unguentum antimonii tartarati=) is a mechanical mixture of tartar emetic and lard, or simple ointment;[801] strength 20 per cent. There is no recorded case of conviction for the adulteration of tartar emetic; cream of tartar is the only probable addition. In such a case the mixture is less soluble than tartar emetic itself, and on adding a small quantity of carbonate of soda to a boiling solution of the suspected salt, the precipitated oxide at first thrown down, becomes redissolved.

[801] Simple ointment is composed of white wax 2, lard 3, almond oil 3 parts.

=Solution of Chloride of Antimony= is a solution of the terchloride in hydrochloric acid; it is a heavy liquid of a yellowish-red colour, powerfully escharotic; its specific gravity is 1·47; on dilution with water, the whitish-yellow oxychloride of antimony is precipitated. One drachm (3·549 c.c.) mixed with 4 ounces (112 c.c.) of a solution of tartaric acid (·25 : 4) gives a precipitate with SH₂, which weighs _at least_ 22 grains (1·425 grm.). This liquid is used on very rare occasions as an outward application by medical men; farriers sometimes employ it in the foot-rot of sheep.

=Purified Black Antimony= (=Antimonium nigrum purificatum=) is the purified native sulphide Sb₂S₃; it should be absolutely free from arsenic.

=Sulphurated Antimony= (=Antimonium sulphuratum=) is a mixture of sulphide of antimony, Sb₂S₃, with a small and variable amount of oxide, Sb₂O₃. The P.B. states that 60 grains (3·888 grms.) dissolved in ClH, and poured into water, should give a white precipitate of oxychloride of antimony, which (properly washed and dried) weighs about 53 grains (3·444 grms.). The officinal compound pill of subchloride of mercury (_Pilula hydrargyri subchloridi composita_) contains 1 grain (·0648 grm.) of sulphurated antimony in every 5 grains (·324 grm.), _i.e._, 20 per cent.

(2) =Patent and Quack Pills=:--

=Dr. J. Johnson’s Pills.=--From the formula each pill should
contain:--