[745] “The Maybrick Trial and Arsenical Poisoning,” by Thos. Stevenson, M.D., Guy’s Hosp. Rep., 1889.
On or about April 12-19th, 1889, Mrs. Maybrick purchased arsenical fly-papers. On April 13-20th Mr. Maybrick visited London, and consulted Dr. Fuller for dyspepsia, who prescribed nux vomica, acids, and mild remedies (but no arsenic); in one bottle of medicine, ostensibly made according to Dr. Fuller’s prescription, arsenic was subsequently found.
Up to Saturday, April 27th, Mr. Maybrick was in his usual health; he was then sick, numbed, and in pain, and had cramps; he told his clerk he had been an hour in the water-closet, but whether for diarrhœa or constipation does not appear; he ascribed the symptoms to an overdose of Fuller’s medicine. About this date fly-papers were found by the servants soaking in Mrs. Maybrick’s bedroom in a sponge-basin, carefully covered up. On the 29th she again purchased two dozen fly-papers from another chemist. On April 28th Mr. Maybrick was sick and ill; at 11 A.M. Dr. R. Humphreys was called in; Mr. Maybrick complained of a peculiar sensation about his heart, and said he was in dread of paralysis. He attributed his illness to a strong cup of tea taken before breakfast. On the following day he was better, and on the 30th still improving. On May 1st and 2nd Mr. Maybrick went to his office and lunched, both days, off revalenta food, prepared at home and warmed at his office in a new saucepan purchased for the occasion; on one of these days the lunch was forgotten, and was sent to Mr. Maybrick by his wife; and on one of the two days, it is not clear which, Mr. Maybrick complained that his lunch did not agree with him, and he attributed it to inferior sherry put into his food.
In a jug found at the office, and in which food had been taken there, a trace of the food still remained after Mr. Maybrick’s death, and arsenic was found therein.
On May 3rd the last fatal illness set in. It is uncertain what food he had after breakfast; he went to the office, and returned home between 5 and 6 P.M. He had been seen by Dr. Humphreys in the morning, and appeared then not quite so well; he found him at midnight suffering from what he thought was severe sciatica; the patient said he had been sick from revalenta. On May 4th he was continually sick, nothing could be retained on the stomach, but the sciatic pain was gone; on May 5th the vomiting continued, the patient complained of the sensation of a hair sticking in the throat, and of a filthy taste in the mouth. The throat and fauces were only slightly reddened, the tongue was furred.
On May 6th there was less vomiting, but otherwise the condition was the same, and Fowler’s solution ordered, but only a quantity equal to 1⁄300 grain was actually taken.
May 7th the condition was improved, but there was no increase of power. Dr. W. Carter was called in consultation. The vomiting was passing away, and diarrhœa commencing. The throat was red, dry, and glazed; there were incessant attempts to cough up an imaginary hair. No cramps, no pain in the stomach or intestines, nor conjunctivitis. On this day the first direct evidence of diarrhœa is recorded, the medical men actually seeing a loose motion. The result of the consultation was that Mr. Maybrick must have taken some irritant in his food or drink.
On the 8th a professional nurse took charge. During the 8th and 9th severe tenesmus set in with diarrhœa, and blood was observed in the fæces. Now arsenic was suspected, the urine was examined by Dr. Humphreys, and a rough analysis was made of some Neaves’ food which the patient had been taking.
The patient died on the 10th, at 8.30 P.M.
The post-mortem appearances were as follows:—
The tongue was dark, the top of the gullet slightly red, but otherwise healthy, save at the lower end, where the mucous membrane was gelatinous, and was dotted over with black dots, like frogs’ spawn.
There was a small shallow ulcer in the mucous membrane of the larynx at the back of the epiglottis. The free margin of the epiglottis was rough and eroded; and on the posterior aspect of the ericoid cartilage there were two small red patches. In the stomach were from 5-6 ozs. of brownish fluid. At the cardiac end there was a large vermilion-red patch, interspersed here and there with small dark ecchymoses (spoken of by Dr. Humphreys as a flea-bitten appearance); to this followed a non-inflamed space, and near the pyloric orifice, and extending 2 inches from it, was another red inflamed portion of mucous membrane. In the small intestine the mucous membrane was red and inflamed, from 3 inches below the pylorus to about 3 feet downwards. About 18 or 20 feet lower down, i.e., a little below the ileo-cæcal valve, the mucous membrane was again inflamed to a lesser extent over a space of about 2 feet; the lower end of the rectum was also red and inflamed. No arsenic was found in the stomach or its contents, or in the spleen. Arsenic was present in the liver, in the intestines, and in the kidneys. The quantity separated altogether amounted to over 0·1 grain. The liver weighed 48 ozs., and from 12 ozs. of the liver 0·076 grain of arsenic, reckoned as As2O3, was separated.
The whole course of the symptoms and the post-mortem examination showed that the deceased died from an irritant poison; and from the fact of a small quantity of arsenic having been found in the body, there can be little doubt but that the poison was arsenic. The symptoms were somewhat anomalous, but not more so than in other recorded cases of undoubted arsenical poisoning. The facts that tended to connect the accused with the death were as follows:—On the night of either May 9th or the 10th Mrs. Maybrick was observed to remove from the table an opened bottle of Valentine’s meat juice, and take it into an inner dressing-room, and then replace it—the acts being surreptitious. In replacing it, she was observed to take it either from the pocket of her dressing-gown or from an inner pocket. The lining of this pocket was found to be impregnated with As2O3. The juice was found to contain 0·5 grain As2O3, and the liquid was of lower gravity than commercial juice; it had probably, therefore, been diluted.
The following is a list of things containing arsenic:—
Mrs. Maybrick was convicted, but afterwards the sentence was commuted to penal servitude for life.
§ 732. Post-mortem Appearances in Animals.—P. Hugo[746] has made some minute researches as to the pathological appearances met with in animals. His experiments were made on seven dogs, eight guinea-pigs, five rabbits, two pigeons, and five cats—all poisoned by arsenious acid. According to Hugo, so far as these animals were concerned, changes were more constant in the intestine than in the stomach.
[746] Beiträge zur Pathologie der acuten Arsenikvergiftung., Archiv für exper. Pathol. u. Pharmakol., Leipzig, 1882.
Stomach.—Changes in the mucous membrane were especially noticed in the great curvature and towards the pylorus; the pylorus itself, and a part of the cardiac portion, remained unchanged. The mucous membrane in dogs and cats was red, with a tinge of blue—in many cases the redness was in streaks, with injection of the capillaries. The stomach of plant-eaters was less altered, and a microscopical examination of the mucous tissues did not show any fatty change.
The Intestines.—In dogs and cats changes were evident; in rabbits and guinea-pigs they were not so marked, but the intestines of the last were extremely tender and brittle, very moist, and filled with a slimy, serous, grey-white fluid; nevertheless, the changes in all these animals appear to be of essentially the same nature. The most striking effect is the shedding of a pseudo-membrane; in quite recent cases there is a layer of from 1 to 11⁄2 mm. wide of a transparent, frog-spawn-like jelly streaking the intestine. In later stages it becomes thicker, while occasionally it resembles a diphtheritic exudation. The mucous membrane itself is deep purple-red, showing up by the side of the pseudo-membrane. With regard to the villi, the epithelial layer is detached, and the capillary network filled with blood and enlarged.
The Liver.—Hugo met only occasionally with fatty degeneration of the liver, but there was marked steatosis of the epithelium of the gall-bladder of dogs. A fact not prominently noticed before, is (at all events, in dogs) a serous transudation into the pleural sac and acute œdema of the lungs; the exudation may be excessive, so that more than 100 c.c. of serous fluid can be obtained from the thorax; there is also usually much fluid in the pericardium. In two of Hugo’s experiments there was fluid in the cerebral ventricles; and in all there was increased moisture of the brain substance with injection of the capillary vessels, especially of the pia.
§ 733. Post-mortem Appearances.—A remarkable preservation of the body is commonly, but not constantly, observed. When it does occur it may have great significance, particularly when the body is placed under conditions in which it might be expected to decompose rapidly. In the celebrated Continental case of the apothecary Speichert (1876), Speichert’s wife was exhumed eleven months after death. The coffin stood partly in water, the corpse was mummified. The organs contained arsenic, the churchyard earth no arsenic. R. Koch was unable to explain the preservation of the body, under these conditions, in no other way than from the effect of arsenic; and this circumstance, with others, was an important element which led to the conviction of Speichert.
When arsenious acid is swallowed in substance or solution, the most marked change is that in the mucous membrane of the stomach and intestines; and, even when the poison has been absorbed by the skin, or taken in any other way, there may be a very pronounced inflammatory action. On the other hand, this is occasionally absent. Orfila[747] relates a case in which a man died in thirteen hours after having taken 12 grms. of arsenious acid:—“The mucous membrane of the stomach presented in its whole extent no trace of inflammation, no redness, and no alteration of texture.” Many other similar cases are on record; and, according to Harvey’s statistics, in 197 cases, 36 (about 18·2 per cent.) presented no lesion of the stomach.
[747] Tome i. Obs. v.
The usual changes produced by arsenious acid may be studied in the museums of the London hospitals. In Guy’s Hospital Museum there are three preparations. In preparation 179832 is seen a large stomach with the mucous membrane at certain points abraded, and at the great curvature the whole coats are thinned; it is also somewhat congested. In preparation 179864 is a portion of coagulated lymph, from the stomach of a lad, aged 14, who had taken accidentally a piece of cheese charged with arsenious acid, prepared for the purpose of destroying rats. He lived twenty-eight hours, and presented the ordinary symptoms. The lymph has a membranous appearance, and the rugæ of the stomach are impressed upon it. It is said when recent to have presented numerous bright bloody spots, although there was no visible breach of substance on the surface of the stomach. The mucous membrane of the stomach is stated to have been injected, and there was also diffuse injection of the duodenum. Preparation 179880 is the stomach of a person who survived thirteen hours after taking a fatal dose of arsenious acid; and in the same museum there is a wax model of the appearances which the fresh preparation exhibited, showing a large oval patch coated with mucus and the poison. The stomach was intensely inflamed, the cæcum injected. The rest of the intestine was healthy.
In the museum of University College there are two preparations, one[748] exhibiting intense swelling and congestion of the gastric mucous membrane, which is of a perfectly vermilion colour. Another preparation (No. 2868) shows the effect of a small dose of arsenic on the stomach; there are spots of arborescent extravasation, and slight congestion of the summits of the rugæ, but in other respects it is normal. There is also a cast of Peyer’s patches from the same case, showing great prominence of the glands, with some injection of the intestinal mucous membrane.
[748] This preparation at the time of my visit had no number.
In St. Thomas’ Hospital there is an interesting preparation (No. 8) showing the gastric mucous membrane dotted all over with minute ulcers, none of which have an inflammatory zone.[749] I have not, however, seen in any museum a preparation of the curious emphysematous condition of the mucous membrane, which has more than once been met with. For example, in a case related by Tardieu,[750] Schwann, a labourer, died from the effects of arsenic in thirty-six hours. The autopsy showed that the mucous membrane of the stomach and small intestine was covered with a pasty coating, and was elevated in nearly its whole extent by bullæ filled with gas, forming true emphysematous swellings which encroached upon the diameter of the intestine. There was neither redness nor ulceration, but the mucous membrane was softened.
[749] In a case related by Orfila, t. i. Obs. xv., death resulted from the outward application of arsenic; the mucous membrane of the stomach was natural in colour, but there were four ulcers, one of which was 50 centimetres in diameter.
[750] Op. cit., Obs. i. p. 468.
The author saw, many years ago, at Barnard Castle, an autopsy made on a gentleman who died from arsenic. In this case the mucous membrane of the stomach presented a peculiar appearance, being raised here and there by little blebs, and very slightly reddened.
§ 734. The inflammatory and other changes rarely affect the gullet. Brodie[751] never observed inflammation of the œsophagus as an effect of arsenic; but, when arsenic is swallowed in the solid state, as in the suicide of Soufflard, graphically described by Orfila,[752] it may be affected. In Soufflard’s case there was a vivid injection of the pharynx and gullet.
In many instances, when the arsenic has been taken in the solid form, the crystals with mucus and other matters adhere to the lining membrane. I have seen in the stomach of a horse, poisoned by an ounce of arsenic, an exquisite example of this. The inflammatory changes may be recognised many months after death owing to the antiseptic properties of arsenic; nevertheless, great caution is necessary in giving an opinion, for there is often a remarkable redness induced by putrefactive changes in healthy stomachs. Casper,[753] on this point, very justly observes:—“If Orfila quotes a case from Lepelletier, in which the inflammatory redness of the mucous membrane of the stomach was to be recognised after nine months’ interment, and if Taylor cites two cases in which it was observed nineteen and twenty-one months after death respectively, this is in contradiction of all that I, on my part, have seen in the very numerous exhumed corpses examined by me in relation to the gradual progress of putrefaction and of saponification, and I cannot help here suspecting a confusion with the putrefactive imbibition redness of the mucous membrane.”
[753] Handbuch, vol. ii. p. 420.
If examined microscopically, the liver and kidneys show no change, save a fatty degeneration and infiltration of the epithelial cells. In the muscular substance of the heart, under the endocardium, there is almost constantly noticed ecchymosis. In the most acute cases, in which a cholera-like diarrhœa has exhausted the sufferer, the blood may be thickened from loss of its aqueous constituents, and the whole of the organs will present that singularly dry appearance found in all cases in which there has been a copious draining away of the body fluids. In the narcotic form of arsenical poisoning, the vessels of the brain have been noted as congested, but this congestion is neither marked nor pathognomonic. Among the rare pathological changes may be classed glossitis, in which the whole tongue has swollen, and is found so large as almost to fill the mouth. This has been explained, in one case, as caused by solid arsenious acid having been left a little time in the mouth before swallowing it. On the other hand, it has also been observed when the poison has been absorbed from a cutaneous application. When arsenic has been introduced into the vagina, the ordinary traces of inflammatory action have been seen, and, even without direct contact, an inflammation of the male and female sexual organs has been recorded, extending so far as gangrene. As a rule, putrefaction is remarkably retarded, and is especially slow in those organs which contain arsenic; so that, if the poison has been swallowed, the stomach will retain its form, and, even to a certain extent, its natural appearance, for an indefinite period. In corpses long buried of persons dying from arsenical poisoning, the ordinary process of decay gives place to a saponification, and such bodies present a striking contrast to others buried in the same graveyard. This retardation of putrefaction is what might, à priori, be expected, for arsenic has been long in use as a preservative of organic tissues.
§ 735. Physiological Action of Arsenic.—The older view with regard to the essential action of arsenic was, without doubt, that the effects were mainly local, and that death ensued from the corrosive action on the stomach and other tissues—a view which is in its entirety no longer accepted; nevertheless, it is perfectly true that arsenic has a corrosive local action; it will raise blisters on the skin, will inflame the tongue or mucous membranes with which it comes in contact; and, in those rapid cases in which extensive lesions have been found in the alimentary canal, it can hardly be denied that instances of death have occurred more from the local than the constitutional action. In the vast majority of cases, however, there is certainly insufficient local action to account for death, and we must refer the lethal result to a more profound and intimate effect on the nervous centres. The curious fact, that, when arsenic is absorbed from a cutaneous surface or from a wound, the mucous membrane of the stomach inflames, is explained by the absorption of the arsenic into the blood and its separation by the mucous membrane, in its passage exerting an irritant action. The diarrhœa and hyperæmia of the internal abdominal organs have been referred to a paralysis of the splanchnic nerves, but Esser considers them due to an irritation of the ganglia in the intestinal walls. Binz has advanced a new and original theory as to the action of arsenious acid; he considers that the protoplasm of the cells of many tissues possess the power of oxidising arsenious acid to arsenic acid, and this arsenic acid is again, by the same agency, reduced to arsenious acid, in this way, by the alternate oxidation and reduction of the arsenious acid, the cells are decomposed, and a fatty degeneration takes place. Thus arsenic causes fatty changes in the liver, kidney, and other cells by a process analogous to the action of phosphorus. T. Araki[754] also considers that both arsenic and phosphorus lessen oxidation, and points out that lactic acid appears in the urine when either of these poisons are taken, such acid being the result of insufficient oxidation. A notable diminution of arterial pressure has been observed. In an experiment by Hugo[755] ·03 grm. of As2O3 was injected intravenously, the normal arterial pressure being 178 mm. Ten minutes after injection the pressure sank to 47 mm.; in sixteen minutes it again rose to 127 mm. Accumulative action of arsenic does not occur. Hebra has given, in skin diseases, during many months, a total quantity of 12 grms. without evil result.
§ 736. Elimination of Arsenic.—Arsenic is separated especially by the urine,[756] then through the bile, and by the perspiration. The eruption often observed on the skin has been referred to the local action of small quantities of arsenic in this way eliminated. It is found in the urine first after from five to six hours, but the elimination from a single dose is not finished till a period of from five to eight days; it has often been looked for twelve days after taking it, but very seldom found. According to Vitali, the arsenic in the urine is not free, but probably displaces phosphorus in phospho-glyceric acid; possibly it may also replace phosphorus in lecithin.
[756] An old experiment of Orfila’s has some practical bearings, and may be cited here. A dog was treated by ·12 grm. of arsenious acid, and supplied plentifully with liquid to drink; his urine, analysed from time to time during ten days, gave abundant evidences of arsenic. On killing the animal by hanging on the tenth day, no arsenic could be detected in any of the organs of the body; it had been, as it were, washed out.
§ 737. Antidote and Treatment.—In any case in which there is opportunity for immediate treatment, ferric hydrate should be administered as an antidote. Ferric hydrate converts the soluble arsenious acid into the insoluble ferric arseniate, the ferric oxide being reduced to ferrous oxide. It is necessary to use ferric hydrate recently prepared, for if dried it changes into an oxyhydrate, or even if kept under water the same change occurs, so that (according to the experiments of Messrs. T. & H. Smith) after four months the power of the moist mass is reduced to one-half, and after five months to one-fourth.
It is obvious that ferric hydrate is not in the true sense of the word an antidote, for it will only act when it comes in contact with the arsenious acid; and, when once the poison has been removed from the stomach by absorption into the tissues, the administration of the hydrate is absolutely useless. Ferric hydrate may be readily prepared by adding strong ammonia to the solution or tincture of ferric chloride, found in every medical man’s surgery and in every chemist’s shop, care being taken to add no caustic excess of ammonia; the liquid need not be filtered, but should be at once administered. With regard to other methods of medical treatment, they are simply those suggested by the symptoms and well-known effects of the poison. When absorbed, the drinking of water in excess cannot but assist its elimination by the kidneys.
§ 738. Detection of Arsenic.—The analyst may have to identify arsenic in substance, in solution, in alloys, in wall-papers, in earth, and in various animal, fatty, resinous, or other organic matters.
Arsenious Acid in Substance.—The general characters of arsenious acid have been already described, and are themselves so marked as to be unmistakable. The following are the most conclusive tests:—
(1) A small fragment placed in the subliming cell (p. 258), and heated to about the temperature of 137·7° (286° F.), at once sublimes in the form of an amorphous powder, if the upper glass disc is cool; but if heated (as it should be) to nearly the same temperature as the lower, characteristic crystals are obtained, remarkable for their brilliancy and permanency, and almost always distinct and separate. The prevailing form is the regular octahedron, but the rhombic dodecahedron, the rectangular prism, superimposed crystals, half crystals, deep triangular plates like tetrahedra, and irregular and confused forms, all occasionally occur.
(2) A beautiful and well-known test is that of Berzelius:—A small hard-glass tube is taken, and the closed end drawn out to the size of a knitting needle. Within the extreme point of this fine part is placed the fragment (which may be no more than a milligramme) and a splinter of charcoal, fine enough to enter freely the narrow part, as shown in the figure. The portion of the tube containing the charcoal (e) is first heated until it glows, and then the extreme end; if arsenic is present, a mirror-like coating is easily obtained in the broader portion of the tube (d). That this coating is really arsenical can be established by the behaviour of metallic crusts of arsenic towards solvents (as given at p. 557). The portion of the tube containing the crust may also be broken up, put in a very short, wide test-tube (the mouth of which is occupied by a circle of thin microscopic glass) and heated, when the arsenic will sublime on to the glass disc, partly as a metal and partly as crystalline arsenious acid.
(3) Arsenious acid, itself inodorous, when heated on coal, after mixing it with moist oxalate of potash, evolves a peculiar garlic-like odour. To this test oxide of antimony adulterated with arsenic will respond, if there is only a thousandth part present. Simply projecting arsenious acid on either red-hot charcoal or iron produces the same odour.
(4) A little bit of arsenious acid, heated in a matrass with two or three times its weight of acetate of potash, evolves the unsupportable odour of kakodyl.
Arsenites and Arseniates, mixed with oxalate of soda and heated in a matrass, afford distinct mirrors, especially the arsenites of the earths and silver; those of copper and iron are rather less distinct.
Sulphides of Arsenic are reduced by any of the processes described on p. 573 et seq.
In Solution.—An acid solution of arsenious acid gives, when treated with SH2, a canary-yellow precipitate, soluble in ammonia, carbonate of ammonia, and bisulphite of potash, and also a metallic sublimate when heated in a tube with the reducing agents in the manner described at p. 575. By these properties the sulphide is distinguished and, indeed, separated from antimony, tin, and cadmium.
The sulphides of tin and cadmium are certainly also yellow, but the latter is quite insoluble in ammonia, while the former gives no metallic sublimate when heated with reducing substances.
The sulphide of antimony, again, is orange, and quite insoluble in potassic bisulphite, and scarcely dissolves in ammonia.
A small piece of sodium amalgam placed in a test-tube or flask containing an arsenic-holding liquid, or the liquid made alkaline with soda or potash and a little bit of aluminium added, produces in a short time arsine, which will blacken a piece of paper, soaked in nitrate of silver, and inserted in the mouth of the flask. This is certainly the most convenient test for arsenic. No antimoniuretted hydrogen (stibine) is given off from an alkaline solution and no SH2.
Marsh’s Original Test for Arsenic consisted in evolving nascent hydrogen by zinc and sulphuric acid, and then adding the liquid to be tested. The apparatus for Marsh’s test, in its simplest form, consists of a flask provided with a cork conveying two tubes, one a funnel reaching nearly to the bottom of the flask; the other, a delivery tube, which is of some length, is provided with a chloride of calcium bulb,[757] and towards the end is turned up at right angles, the end being narrowed. By evolving hydrogen from zinc and sulphuric acid, and then adding portions of the liquid through the funnel, arseniuretted hydrogen in a dry state is driven along the leading tube, can be ignited on its issue, and on depressing a piece of cold porcelain, a dark metallic spot of arsenic is obtained.[758] Or, if any portion of the tube be made red-hot, the metal is deposited in the same way as a ring. The apparatus admits of much complication and variety. One of the most useful additions is, perhaps, the interposition of a small gasometer. This consists of a cylindrical glass vessel with entrance and exit tubes, open at the bottom, immersed in water in a larger vessel, and counterpoised by weights and rollers, exactly like the large gasometers used at gasworks; the exit tube must have a stop-cock, and the gas must pass over calcic chloride in order to dry it thoroughly.
[757] Otto recommends the first half of the drying tube connected with the development flask to be filled with caustic potash, the latter half with chloride of calcium (Ausmittelung der Gifte). Dragendorff approves of this, but remarks that it should be used when arsenic alone is searched for, since caustic potash decomposes stibine. The potash fixes SH2, and prevents the formation of chloride of arsenic; on the other hand, it absorbs some little AsH3.
M. Blondlot has observed[759] that if pure zinc, a weak solution of arsenious acid, and a sulphuric acid containing nitric acid or nitrous compounds, be mixed together, the arsenic passes into a solid hydrate, which is deposited on the surface of the zinc; this is, however, prevented by the addition of a little stannous chloride dissolved in hydrochloric acid.
[759] Blondlot, “Transformation de l’arsenic en hydrure solide par l’hydrogène aissant sous l’influence des composés nitreux.”—Jour. de Pharm. et de Chim., 3e sér., t. xliv. p. 486.
The precautions to be observed in Marsh’s test are:—
(1) Absolute freedom of the reagents used from arsenic, antimony,[760] and other impurities.
[760] With regard to purity of reagents, Sonnenschein states that he has once found chlorate of potash contaminated with arsenic.—Sonnenschein, Gericht. Chemie, p. 139.
(2) The sulphuric acid should be diluted with five times its weight of water, and if freshly prepared should be cooled before use. Strong acid must not be employed.[761]
[761] M. A. Gautier uses sulphuric acid diluted with five times its weight of water; when the hydrogen has displaced the air, he adds to the arsenical matter 45 grms. of this acid and 5 grms. of pure sulphuric acid.—Bull. de la Société Chim. de Paris, 1875, t. xxiv.
(3) The fluid to be tested should be poured in little by little.
(4) Nitrous compounds, nitric acid, hydrochloric acid, chlorides, are all more or less prejudicial.
(5) The gas should come off regularly in not too strong a stream, nor out of too small an opening.
(6) The gas should pass through the red-hot tube at least one hour, if no stain is at once detected.
(7) Towards the end of the operation, a solution of stannous chloride in hydrochloric acid is to be added to the contents of the flask. This addition precipitates any arsenic present in a finely divided state, in which it is readily attacked by nascent hydrogen.[762]
[762] F. W. Schmidt, Zeit. anorg. Chem., i. 353-359.
The characteristics of the metallic stains which may occur either on glass or porcelain in the use of Marsh’s test, may be noted as under:—
| Mirror or Crust of Arsenic | Mirror or Crust of Antimony |
|---|---|
| Is deposited at a little distance from the flame. | Is deposited close to the flame, and on both sides of it, and is therefore notched. |
| An arsenical stain is in two portions, the one brownish, the other a glittering black. | The stain is tolerably homogeneous, and usually has a tin-like lustre. |
| On heating, it is rapidly volatilised as arsenious acid. | Volatilisation very slow; no crystalline sublimate obtainable. |
| On transmission of a stream of SH2, whilst immediately behind the stain a gentle heat is applied, the arsenic is changed to yellow sulphide;[763] if dry ClH is now transmitted, the arsenical sulphide is unchanged. | The same process applied in the case of antimony produces the orange or black sulphide; and on passing dry ClH, chloride of antimony volatilises without the application of heat. |
| Chloride of lime dissolves the arsenic completely. | Antimony not affected. |
| Protochloride of tin has no action on metallic arsenic. | Dissolves slowly but completely the antimony stain. |
| The arsenic stain, dissolved in aqua regia, or ClH and chlorate of potash, and then treated with tartaric acid, ammonia, and magnesia mixture, gives a precipitate of ammonia magnesian arseniate.[764] | No precipitate with antimony. |
[763] It is desirable to dissolve away the free sulphur often deposited with the arsenical sulphide by bisulphide of carbon.
[764] Schönbein has proposed ozone as an oxidiser of arsenical stains. The substance containing the stain, together with a piece of moist phosphorus, is placed under a shade, and left there for some time; the oxidisation product is, of course, coloured yellow by SH2 if it is arsenious acid, orange if antimony. The vapour of iodine colours metallic arsenic pale yellow, and later a brownish hue; on exposure to the air it loses its colour. Iodine, on the other hand, gives with antimony a carmelite brown, changing to orange.
An arsenical ring may be also treated as follows:—Precipitated zinc sulphide is made into a paste with a little water, and introduced into the end of the tube; the same end is then plunged into dilute sulphuric acid, and the ring heated, when the arsenical sulphide will be produced.
The mirror or crust of arsenic is usually described and weighed as being composed of the pure metal, but J. W. Rettgers has investigated the matter, and the following is an abstract of his results:—
There is no amorphous form of arsenic, the variety generally thus called being crystalline. Two modifications can be distinguished: the one being a hexagonal silver-white variety possessed of metallic lustre, specifically heavier and less volatile than the second kind, which is black in colour, crystallises apparently in the regular system, and constitutes the true arsenic mirror. The former modification corresponds to red hexagonal phosphorus (red phosphorus having been recently proved by the author to be crystalline), and the latter to yellow phosphorus, which crystallises in the regular system. Both modifications of arsenic are perfectly opaque; deposits which are yellow or brown, and more or less transparent, consist of the suboxide and hydride, As2O and AsH. The brown spot on porcelain produced by contact with a flame of arseniuretted hydrogen is not a thin film of As, but one of the brown solid hydride AsH, formed by the decomposition of AsH3. This view is confirmed by the fact that arsenic sublimed in an indifferent gas (e.g., CO2) is deposited in one or other of the modifications described above, the brown transparent product being obtained only in the presence of H or O. Moreover, pure arsenic is insoluble in all solvents, whereas the film on porcelain (AsH) is soluble in many solvents, including hydrocarbons of the benzene series (e.g., xylene), warm methylene iodide, and hot caustic potash.
Hence quantitative results from weighing arsenical mirrors can never be accurate, because the mirrors consist of mixtures of hydride and suboxide.
Reinsch’s Test.—A piece of bright copper foil, boiled in an acid liquid containing either arsenic or antimony, or both, becomes coated with a dark deposit of antimony or arsenic, as the case may be. The arsenical stain, according to Lippert, is a true alloy, consisting of 1 arsenic to 5 copper.[765] Properly applied, the copper will withdraw every trace of arsenic or antimony from a solution. Dr. John Clark[766] has lately introduced some improvements in Reinsch’s process. His experiments have been directed to the means of proving the presence of arsenic or antimony in the stain on the copper with greater certainty, and at the same time estimating the amount when they occur together.