Part 3 — MINERAL POISONS.

Under this head is included the greater proportion of those substances which are employed as the instruments of crime; for they are generally of easy access, require but little preparation, and are so destructive in small doses, and, at the same time, so little disgusting in flavour, as to furnish the assassin with the sure and secret means of destruction. Fortunately, however, for the ends of justice, such agents are pre-eminently the objects of successful analysis. In treating of the history of the individual substances derived from this 210kingdom, we shall consider, 1st. their external characters, such as form, colour, odour, taste, specific gravity; 2d. their chemical composition, and habitudes; 3d. the tests by which their presence may be recognised; 4th. the symptoms which they occasion; 5th. their physiological action; 6th. their different modes and forms of application; 7th. the lesions of structure they occasion; 8th. the phenomena presented on dissection.

Cl. 1. CORROSIVE POISONS.

ARSENIC.

The greek word Αρσενικον was employed by Dioscorides, and other writers of that period, to denote a particular mineral of a reddish colour, which Aristotle had already described by the name of σανδαρακη,^[214] and his disciple Theophrastus, by that of αρρενικον. It was employed by the ancients both as a pigment and as a medicine, and appears to have been a compound of Sulphur, and a peculiar metal, to which the name of Arsenic is now exclusively applied. At what period this metal was first discovered seems very doubtful; and although a process for obtaining it is described in the Pharmacopœia of Schroeder, published in 1649, yet its peculiar nature was examined, for the first time by Brandt, in 1733.

The metal, Arsenic, is distinguished by the following properties, viz.

211It has a bluish-grey colour, not unlike that of steel, and a considerable lustre; its texture is grained, and sometimes scaly; its hardness not very considerable, but its fragility is so great that it falls to pieces under a moderate blow of the hammer, and admits of being easily reduced to a very fine powder; according to Bergman its specific gravity is 8·31. When cold, it emits no sensible odour, but if heated, it yields a strong alliaceous, or garlic-like smell, which is to be considered as the most characteristic of its properties. Its point of fusion is unknown, for it is the most volatile of all the metals, and sublimes, before it melts, at the temperature of 540° Fah., and if the process be conducted slowly in close vessels, the metallic sublimate will assume a tetrahedral^[215] form of crystallization; if the air be admitted, and the temperature still farther raised, it will burn with an obscure bluish flame.

Arsenic is extremely susceptible of oxidation, and, by mere exposure to the air, shortly loses its metallic lustre; and yet it may be kept under the surface of cold water, for any length of time without exhibiting the signs of oxidation, or solution; a covering of this fluid, or of alcohol, is therefore considered as affording the best means of preserving the metal in a state of integrity.

Arsenic is capable of combining with two proportions of oxygen, and of forming two definite compounds, which we shall hereafter consider under the title of Arsenious and Arsenic acids. The substance described by some authors as the black oxide of this metal would seem to be an indefinite mixture of the metal itself, and the arsenious acid.

212Arsenic does not appear to possess any deleterious properties, but it is almost impossible to reduce the metal to powder, so as to adapt it for exhibition without its becoming oxidized. M. Renault therefore, in order to decide the question, had recourse to its alloys; and he found that Mispickel (an alloy of Arsenic and Iron), when given to the extent even of two drachms, scarcely produced any effect; a result which very satisfactorily accords with the conclusion drawn by Bayen, in his work on Tin, and which proves that the arsenic contained in that metal, need not excite the least alarm, since it exists in a metallic state. We have upon another occasion^[216] observed, that the vapours characterised by an alliaceous odour are probably less noxious than the arsenical fumes which are inodorous; and that the little injury experienced by workmen who solder silver filligree with an arsenical alloy, may probably depend upon the deoxidized state of its fumes.

ARSENIOUS ACID, or WHITE OXIDE OF ARSENIC.

This is justly considered as the most fatal of all mineral poisons, and is the one more frequently selected than any other, as the instrument of assassination and suicide; while its numerous applications in medicine and the arts, by making it an article of general and indiscriminate sale, have rendered it an accidental as well as criminal source of suffering and death.

It is seldom prepared by the chemist, since it exists in a native state, and is moreover procured abundantly and economically, during the extraction of the 213other metals from their ores.^[217] In the commercial world the substance is still known by the name of White Arsenic; and continues to be expressed in popular language, by the simple term Arsenic.

It generally occurs in the form of white compact masses, opaque on their exterior surface; transparent, and presenting a vitrified aspect in the interior. Its taste is acrid and corrosive, but not to a degree corresponding with its virulence. Specific gravity 3·7. When reduced to powder it bears a strong resemblance to refined sugar, for which it has sometimes been fatally mistaken, and with which it has been often mingled for criminal purposes. At the temperature of 383° Fah. it is volatilized, and is capable of crystallizing in tetrahedrons with truncated angles, or rather in octohedrons; by a strong heat, in close vessels, it is vitrified and becomes pellucid, and acquires the specific gravity 5·000^[218]; but when exposed to the air, it shortly returns to its former appearance. In the state of vapour it is quite inodorous, although the contrary is positively asserted in several chemical works of high authority, and it is stated to be characterised by a smell like that of garlic; the fact is, that the alliaceous or garlic-like smell is wholly confined to metallic arsenic in a state of vapour; and whenever the arsenious 214acid seems to yield such an odour, we may very confidently conclude that its decomposition has taken place, and that it has been reduced to its metallic state. Such a reduction will generally happen when it is projected upon ignited charcoal, or when heated in contact with those metallic bodies which readily unite with oxygen, such as Antimony, Zinc, &c. It is stated by Orfila and other writers, that if it be projected upon heated copper the alliaceous odour is evolved. This assertion is undoubtedly true, but the fact requires to be explained with more precision, or we may fall into an important error respecting it. The author has shewn by several experiments, already published in his Pharmacologia,^[219] that the phenomenon takes place only when the copper is in a state of ignition, at which temperature its affinity for oxygen enables it to reduce the arsenious acid, and consequently to develope the metallic odour. We have ascertained by repeated experiments that if a few grains of arsenious acid be heated on a plate of copper, by means of a spirit lamp or the blow-pipe, no odour is perceptible; for, in this case, the whole of the acid will be dissipated before the copper can acquire a temperature sufficiently exalted to deoxidize, and reduce it. If the arsenious acid be heated on a plate of zinc, the smell will not be evolved until the latter metal is in the state of fusion. If, instead of the foregoing surfaces, we employ in our experiments those of gold, silver, or platina, no alliaceous smell whatever is produced, at any temperature, provided every source of fallacy be carefully avoided; but it deserves particular notice, that the author has found the flame of the spirit lamp to be in itself, capable of decomposing the arsenious acid, in 215consequence, it is presumed, of the operation of its hydrogen;^[220] a fact which is very likely to betray the experimenter, as in the first instance it did the author, into a belief that the arsenious acid does actually yield the odour in question.

The term Arsenious acid was first bestowed upon this substance by Fourcroy, since it was found to possess many of the essential habitudes of an acid; as for instance, that of combining with the pure alkalies to saturation. It dissolves in water; but, according to Klaproth, although it requires for its solution 400 parts of that fluid, at the temperature of 60° Fah. it requires not more than 13, at 212°; and it moreover appears that if 100 parts of water be boiled on the arsenious acid, and suffered to cool, it will retain 3 grains in solution, and deposit the remainder in crystals. This fact shews the great importance of employing boiling water in every chemical examination of substances supposed to contain arsenic. It proves also that a fatal dose of the poisonous mineral may be very easily administered in any watery vehicle, a fact which was denied on the trial of Ogilvy and Nairne^[221] by Dr. James Scott, who deposed that “Arsenic would not dissolve in warm water, but almost instantly subside to the bottom of the vessel,” although, at the same time, he acknowledged that “if it were put into tea with milk and sugar, and stirred about, it might be suspended long enough to kill those who should drink the potion.” It is soluble in alcohol, and in fixed oils, the former taking up 216two per cent. By the addition of an alkali, an arsenite of great solubility will result, and a solution of extreme virulence may be thus effected. With lime-water arsenious acid produces a white precipitate of arsenite of lime, but which is soluble in an excess of the acid. With magnesia it also forms a very soluble, and extremely active, arsenite.

Symptoms of Poisoning by the Arsenious Acid.

Hahnemann, in his work on Arsenic, proposes a classification of its effects founded on their relative duration and violence, and which it is our intention to adopt on the present occasion, without any other alteration than that of reversing the order of the classes.

Poisoning by Arsenic may accordingly be considered as admitting of three degrees of intensity, viz. 1st. Where the case, although attended with dangerous symptoms, does not terminate fatally. 2d. Where death does not follow until after a lapse of twenty-four hours. 3d. Where death takes place within twenty-four hours after the exhibition of the poison.

1. Symptoms of the first and lowest degree. In the slighter cases in which the operation of arsenic is recorded as producing poisonous effects, the symptoms were, uneasiness of the præcordia; cholics; thickness, redness, and stiffness of the palpebræ; soreness of the gums; ptyalism; itching over the surface of the body, sometimes attended with a slight eruption; restlessness; cough; head-ache; strangury, and ardor urinæ. Where the dose of poison has been somewhat greater, although still inadequate to the destruction of life, violent vomiting is commonly the first symptom, preceded in some instances with a sense of heat and dryness in the fauces; in such 217cases where the vomiting has very shortly succeeded the ingestion of the Arsenic, and the stomach has at the same time been filled with food, the patient may owe his escape to the poison being discharged before it had time to act. Morgagni relates a case of poisoning at an Italian feast, where the dessert was intentionally sprinkled with Arsenic instead of flour; those who had previously eaten but little speedily perished, but those who had eaten heartily were saved by vomiting. Although in this degree of poisoning the life of the patient may be spared, yet a variety of consecutive symptoms may continue to harrass him for a longer or shorter period, such as indigestion, debility, partial paralysis, and epilepsy. The history^[222] of the cases of Mr. Turner and his family, of Chancery lane, for the poisoning of whom Eliza Fenning was executed, will afford a striking illustration of this fact. The hair of the head has also been observed, in some cases, to fall off. Dr. Male is also of opinion that the long protracted and injudicious use of this mineral, as a medicine, will induce exostosis and caries of the bones.

2. Symptoms of the second degree. In this case where the patient lives two or three days, or perhaps longer, as in the case of William Mitchell above described (p. 190), the earliest symptoms are heat and thirst, or vomiting, and inexpressible uneasiness and anxiety, the former of which is less frequently observed than the two latter; purging, or sometimes a repeated but ineffectual desire to go to stool; wandering pains; quick, but feeble pulse; head-ache; distended and painful abdomen; priapism; towards the close of the scene the patient often becomes more tranquil and is inclined to sleep, although, in some instances, 218the pains, attended with convulsions, continue to the latest moments. In general, death takes place suddenly. In cases where the effects of the poison are not immediately fatal, we must necessarily expect the occurrence of many phenomena, indicative of the re-action of the system, and which will be better illustrated by a reference to the history of individual cases, such for instance, as those of William Mitchell, (p. 190) and Mr. Blandy, (Appendix) than by any general description which can be given in this place. It is also worthy remark that in such cases, from the length of time, there will necessarily occur a greater opportunity for the co-operation of other contingent causes, whether they be connected with previously existing diseases, or the action of remedies; and the intelligent practitioner will not neglect to appreciate their influence in modifying the character of each particular case. There are besides symptoms highly characteristic when they do arise, but which are of comparatively rare occurrence, such as the ulcerated condition of the fundament, as in the case of Mr. Blandy, and the inflamed eyes and state of the mucous membranes, in that of William Mitchell.

3. Symptoms of the third and highest degree. Soon after a large dose of Arsenic has been swallowed, an austere taste, and a sense of heat and constriction of the pharynx and œsophagus are perceived; in a short period excruciating pains in the stomach and bowels, accompanied with vomiting of the most violent character, the matter voided being generally of a brown colour, and not unfrequently mixed with blood; with these symptoms are conjoined an inexpressible anxiety about the præcordia, and frequent faintings; the stomach at the same time acquires such a high degree of irritability, as to reject the mildest fluids. 219The alvine discharges now become frequent and painful, and consist of dark and extremely fœtid matter, frequently mixed with blood. The thirst is unquenchable, and the heat of the surface becomes extreme. The pulse is small, frequent, and irregular; palpitations of the heart, violent cramps in the legs, sometimes a painful strangury and bloody micturition ensue. The powers of life begin to fail, respiration becomes laborious, cold sweats break out, hiccup occurs, the countenance assumes a singular character of anxiety and distress, a livid circle appears around the eyes, the pulse is imperceptible, the body swells and sometimes becomes covered with a species of miliary eruption, or with dark purple spots. In some cases convulsions ensue, but delirium, or loss of reason, is very rarely the consequence of this species of poisoning, and the unfortunate sufferer is conscious until a few moments before the termination of his existence. Such are the general symptoms, but it is rare to see them all united in the same case; sometimes the greater part of them are absent. M. Chaussier reports the case of a robust middle aged man, who swallowed a quantity of arsenious acid in large lumps, and died without discovering any other symptom than slight syncope; other cases are related where only vomiting and purging^[223] have been observed, and the symptoms have been mistaken for those of cholera spontanea.

The practitioner is therefore not to withhold his belief in a case of poisoning, on account of the absence of several of those symptoms which are enumerated in systematic works on Toxicology.

It is only by the study of individual cases, that he 220can learn to appreciate the just value of those pathognomonic combinations which afford the least exceptionable evidence upon such occasions.

The different modes of Poisoning by Arsenious Acid.

It has been proved by numerous experiments that the life of an animal may be destroyed with equal certainty by arsenious acid, whether it be internally administered, or externally applied to abraded surfaces, sores, or bleeding wounds; and it has been, moreover, shewn, that in either instance the symptoms will be analogous, except in the latter case they will often be more rapid in their course.

Lionardo di Capoa relates the case of a child killed by the violent vomiting and purging arising from a slight wound made in the head by a comb, wet with oil in which arsenic had been infused for the purpose of killing vermin; and we have numerous instances on record, where the application of arsenical cerates and ointments has been followed by violent and dangerous symptoms. We also learn from the different historians of the Plague of London, that the arsenical amulets which were worn, as preservatives, on that occasion, were sometimes attended with deleterious consequences; Crato^[224] observed an ulcer of the breast produced by them. Verzascha, violent pains and syncope. Diemerbroeck,^[225] and Dr. Hodges,^[226] death itself. Amongst the foreign authors who have related cases of poisoning by the external application of arsenic we may mention Desgranges,^[227] who records the history of a chambermaid, poisoned by having 221rubbed her head with an arsenical ointment for the purpose of destroying vermin; and Roux,^[228] who confessed to have killed a girl of eighteen by an application of the “Pâte Arsenicale” to a cancerous breast. M. Renault has also given us the results of his experiments upon Arsenic when applied externally to dogs; when the skin was sound, it excited a pustular eruption without inflammation; but, when the skin was broken, more serious effects followed, both general and local, and in some cases death.^[229]. In an experiment performed by Mr. Hunter, and Mr. Home, in which arsenic was applied to a wound in a dog, the animal died in twenty-four hours, and the stomach was found to be considerably inflamed. Mr. Brodie repeated the experiment several times, always with the precaution of tying a bandage, to prevent the animal licking the wound; the results were uniform; the stomach was, in every case, not only more violently, but more rapidly, inflamed, than when the poison had been internally administered, and it even preceded any inflammatory appearance of the wound. In the Journal de Medecine, the following case is related of a woman who was killed by her husband having insinuated powdered arsenic into the vagina,^[230] at the moment of enjoying the conjugal 222rites. “A woman at Leneux, departement de l’Ourthe, aged forty, having died after a short illness, attended with considerable tumefaction of the genital parts, uterine hemorrhage, vomiting, and purging, the body was inspected by order of the mayor, when the surgeons reported that they found the vulva in a state of gangrene, the abdomen much distended with air, and the intestines inflamed and gangrenous. The culprit was arrested, convicted, and executed.” In the Acts of the Society of Copenhagen, a similar crime stands recorded, and which was also committed by a peasant; in this latter case, although some small pieces of arsenic were found within the vagina, yet some doubts arose respecting the possibility of such a species of poisoning, and the magistrates accordingly consulted the College of Medicine of Copenhagen, who decided the question in the affirmative, having first instituted a series of experiments upon horses.

Death may also be produced by the introduction of arsenic into the rectum; it is said that Sir Thomas Overbury, after the failure of the various poisons^[231] that were administered to him, was at last despatched by an arsenical glyster.

With respect to the quantity of arsenic required for the production of such effects it is difficult to offer a decided opinion, as its operation must in every case be liable to contingency; but a very few grains are in general amply sufficient.

223 Physiological action of Arsenious Acid.

It had long been supposed that arsenic occasioned death by inflaming the stomach; but Mr. Brodie^[232] has very satisfactorily proved, that its influence arises from its being absorbed, and that it must be regarded as a vital rather than as a chemical agent, and as having a constitutional, not a local mode of operation.

In the first place, he has in many instances found the inflammation of the stomach so slight,^[233] that on a superficial examination it might have been easily overlooked; and in most of his experiments with arsenic, death took place in too short a period to be considered as the mere effect of inflammation. In the next place we have already shewn that in whatever manner the poison is applied, whether externally to a wound, or internally, to the alimentary canal, the same inflammatory appearance will be visible in the stomach; a fact which can only be explained by admitting that the poison is absorbed, and that it acts upon these organs through the medium of the circulation; it acts at the same time upon the brain, and heart, but with different degrees of force in different cases; so that it is sometimes difficult to ascertain which of these organs is the first to fail in its functions. According then to these experiments and observations, inflammation of the alimentary canal is not to be considered as the general cause of death in poisoning by arsenic; and yet cases will occur, where the local affection 224may prove fatal, the animal having survived the effects produced on the organs more immediately subservient to life, as the brain and heart. Mr. Henry Earle communicated to Mr. Brodie a case highly illustrative of this fact, which occurred in St. Bartholomew’s hospital; a woman had taken arsenic, and having recovered from the alarming symptoms which first occurred, died at the end of four or five days, when upon dissection, there appeared extensive ulcerations of the stomach and bowels. This then was evidently a case of “Consecutive” poisoning.

The dissertation of Dr. Jaeger, to which we have before alluded, contains the result of a very extensive series of experiments, in illustration of the physiological action of the arsenic. He diligently examined its effects upon all classes of organized beings, as well of the vegetable as of the animal kingdoms. The general conclusions which he has drawn from his experiments on vegetables are, that arsenic is in most cases a rapidly destructive poison to them, with the exception perhaps of a few of the simplest forms of existence;^[234] and that their death was induced by means of the gradual absorption and distribution of the poison by the vessels and cellular membrane, so that the parts died in succession, as the particles of the poison reached them. Dr. Jaegar also found that arsenic was a quick and destructive poison to animals, and that death was preceded, in every instance, from the infusory animalcula up to man, by inordinate motions; and that the secretion was most remarkably increased from the mucous membranes. 225His experiments also proved that arsenic exerted the most powerful effects, when it was injected into the veins, or applied to a bleeding wound; next, when it was introduced into the stomach; but less so, when injected into the large intestines, which have fewer absorbing vessels.^[235]

Organic Lesions, discovered on Dissection.

The examination of the bodies of persons poisoned by arsenic, must not be expected to furnish constant and uniform results, since they will be found to vary very considerably in different cases. As we have already considered the value of accelerated and retarded putrefaction, as an indication of poisoning, we shall at once proceed to the description of the morbid phenomena which are presented by the internal organs on dissection. The stomach and intestines are the parts in which we may expect to find the most decided marks of the ravages from arsenic. The former viscus will be found more or less inflamed; in some instances, the dusky redness will appear in patches, interspersed with points and streaks of a brighter hue; the villous coat of the stomach will be almost always softened, and, as if macerated, can be easily rubbed off in pieces with the fingers from the coats beneath; actual ulceration and sloughing are, according to the observations of Mr. Brodie, never found unless where death is late in taking place, in which case extensive ulceration of all the coats, amounting to actual perforation, may be expected to happen. This statement agrees with the observation of Ruysch, who says that where there had been sufficient time, he found the stomach ulcerated in those 226who had died from the effects of arsenic, but that if death supervened earlier, he only discovered bloody points, distant from each other, throughout the viscus. On the subject of sloughs upon such occasions, our enlightened author remarks, that anatomists have often been betrayed into a fallacy respecting their true nature; on opening the stomach of a dog which had taken a large quantity of arsenic, Mr. Brodie observed a dark brown spot about an inch in diameter, having all the appearance of a slough; on a closer examination, however, it appeared that this spot was no other than a very thin layer of coagulated blood, of a dark colour, and adhering very firmly to the surface of the mucous membrane, and having a few particles of arsenic entangled in it. He states that he has at several times observed a similar appearance but occupying a less extent of surface; and he informs us that, in the Hunterian museum, there is a human stomach, which was preserved for the sake of exhibiting what was considered a slough, produced by the action of arsenic; but that, on examining the preparation carefully, the dark coloured spot was discovered to be simply a layer of coagulated blood, similar to that before described. Dr. Baillie and Dr. Yelloly have found the stomach thickened in several parts, as if by coaguable lymph, and in one case the thickening of the coats was the only alteration of structure observable; and M. Renault relates a case, where the arsenic was taken in large pieces, which produced no other effect than slight syncope on the approach of death; and that, upon opening the body, the arsenic was found in the state it was swallowed, but there was neither inflammation nor erosion of the stomach. Where the arsenic has been swallowed in substance, it will be generally found attached to the 227membrane of the stomach by a peculiar glairy fluid; if the poison should have been administered in solution, the same organic lesions will be discovered, but the presence of the arsenic in the stomach can scarcely be expected, although the contents of the viscus, as well as all the matter ejected from the body before death, must be carefully examined by a chemical process to be hereafter described. The duodenum, like the stomach, generally affords evidence of the same inflamed and disorganized condition; and the whole track of the intestinal canal will be found more or less affected, according to the quantity of arsenic that has been administered, the period of time which has elapsed before death, and other circumstances which have been already enumerated as capable of modifying the action of this destructive substance. It however deserves notice that in many cases the rectum appears to be more affected than the other intestines; Dr. Male^[236] states, that he has frequently found it abraded and ulcerated, and even more inflamed than the stomach itself; Mr. Brodie likewise observed, in his physiological experiments upon this substance, that the inflammation produced by it was greatest in the stomach and the rectum. Dr. Baillie has recorded several instances where a mortification of the rectum followed as an effect of this poison; and in the case of Mr. Blandy, detailed in the Appendix, p. 237, Dr. Addington stated, that the extremity of the rectum was extremely painful, and surrounded by excoriations and ulcers.

Mr. Brodie has stated, in the paper to which we have so often alluded, that the organic lesions occasioned by arsenic are confined to the stomach and intestines, 228and that he never found any appearance of inflammation in the pharynx or œsophagus. This statement, however, is at variance with a great weight of authority; we have ourselves witnessed cases in which dissection has demonstrated extensive inflammation in these parts; indeed it would appear, that this poison acts more particularly on the mucous membranes; and it is reasonable therefore to conclude, that those with which it comes in actual contact will not escape its virulence. The serous membranes which receive less blood, and more lymphatics, are necessarily less affected by it.

In the case of William Mitchell, as related at page 188, the patient complained of soreness of the eyes, heat and uneasiness in the mouth and throat; and the surgeon observed the membrane on the palate and uvula to be detached; so in that, again, of Mr. Blandy, Dr. Addington found on inspection that “his tongue was swelled, and his throat inflamed and excoriated; his lips, especially the upper one, dry and rough, and having angry pimples on them; the inside of his nostrils in the same condition, and his eyes a little blood shot.” (Append. l. c.). In the celebrated Scotch case of Oglivy and Nairne (see page 184) Peter Meik, surgeon of Alyth, deposed, that, upon inspecting the body four or five days afterwards, he found “the tongue swelled beyond its natural size, and cleaving to the roof of the mouth, which he had never observed after a natural death.” Many more instances might be adduced to shew that the fauces, pharynx, and œsophagus are very frequently inflamed and excoriated by the ingestion of arsenic. Mortification of the pudenda^[237] has been 229said to be an effect peculiar to the action of arsenic; certain it is that in males, priapism is sometimes a symptom of this poison, and the penis is found swollen and red after death, as was observed in the case of William Mitchell (p. 190). The scrotum was also enlarged and of a dark colour. We have been long aware that persons exposed to the fumes of arsenic, or accustomed to handle any of its preparations, have been liable to a peculiar affection of these parts, but we have generally explained the fact by supposing that the poison had in such cases, been locally applied to them. The author has been lately informed by his friend Mr. Parkes, that several persons in his establishment were thus attacked, during the time they were engaged in preparing an arsenical solution, as a dye for the calico printers; and we have stated on another occasion,^[238] that the smelters and workmen engaged in the copper works, and tin burning houses of Cornwall, are occasionally affected with a cancerous disease in the scrotum, somewhat similar to that which infests chimney sweepers. It is also singular that Stahl, in describing the putrescent tendency in the bodies of those who die from this poison, mentions in particular the gangrenous appearances of the parts of generation. The other organs of the body do not exhibit any particular appearances, which ought to be regarded as characteristic of death by arsenic; we must necessarily expect to find the traces of morbid action, especially where life has been unusually protracted; and the serous effusions found in the body of William Mitchell, are to be referred to such a cause.

Mr. Brodie has stated that, in animals killed by arsenic, the blood is usually found fluid in the heart 230and vessels after death; this agrees with the observation of Ruysch, who says that he never found the blood coagulated in the human body, after death occasioned by this poison; as well as with that of Dr. Jaeger, who describes the cavities of the heart, especially of the right side, to be, upon these occasions, turgid with blood, but that coagula are very seldom found in them.

A question, of a very considerable importance in a forensic point of view, has arisen with respect to the means, by which we may distinguish whether arsenic, found in the body, had been introduced into the digestive canal during life, or after death. In general, this fact is placed beyond suspicion by the testimony of those to whose care the body had been confided, previous to dissection. But cases have occurred where a poisonous substance has been introduced into the rectum of a dead body, with the diabolical intention of accusing an innocent person of having been the perpetrator of the poisoning. We are not aware of any English case of this kind, but M. Orfila states that in the proceedings of the Criminal Court of Stockholm such a case stands recorded. Fortunately there would not be much difficulty in detecting the crime; for were the arsenic applied to the rectum after death, the change of structure would not extend beyond the part in actual contact with it, but would be distinctly separated from the rest of the intestine by a well defined line of demarcation, which can never happen where the arsenic has acted during life; for, in this latter case, the transition from the diseased to the healthy structure will be gradual, and the limits of each imperceptible.

Before we conclude our observations upon the organic lesions occasioned by arsenic, we may caution 231the anatomist not to confound the red or violet colour which characterises inflammation, with that which has been occasionally found to arise from the ingestion of certain coloured drinks. The following case related by Foderé, and cited by Orfila, may serve to illustrate this subject. “A private person of Châlons sur-Marne, who was in a state of convalescence from a disease under which he had laboured, took a slight purgative, and died very shortly afterwards. He was believed to have been poisoned through some error in the medicine, and in order to be assured of this, the body was opened. The œsophagus and stomach were found to be red, and in certain places livid, as if in a state of gangrene. These appearances at first induced a belief that the deceased had died from poison; but M. Varnier, a physician of Châlons, concluded from the appearances, that death was the consequence of the disease, and that the apparent convalescence was only an insidious respite. It became therefore necessary to give some account of the state of the œsophagus and stomach; and having learnt that the deceased was in the habit of using a strong infusion of red poppies, the idea immediately struck him that the extraordinary colour of these organs might possibly depend on this infusion. In order to determine the validity of this explanation, he caused a dog to swallow, several times, a similar infusion; when upon opening its body, he discovered that the corresponding parts of this animal had assumed the same colour as had been observed in the stomach of the deceased above-mentioned, and, moreover, that this violet red colour was so firmly fixed that it resisted the action of repeated washings.” Tincture of Cardamoms will also be liable to occasion a coloured appearance in the 232stomach, as described in Mr. Stanley’s case of the death of a woman by a dose of opium.^[239]

Of the Chemical Processes, by which the presence of Arsenious Acid may be detected.

This poison may either be submitted to the judicial physician for examination, in its solid form, or in that of solution; and in this latter state it may be mixed with various alimentary substances, whose presence will necessarily embarrass the inexperienced operator, and multiply the apparent difficulties of his task. It becomes our duty, therefore, upon this occasion, to enter very fully and minutely into the history of the various processes, which have been proposed for the solution of the important problem under consideration; to appreciate the relative value of each, and to point out the sources of fallacy and failure, to which they are severally exposed.

Such a review of the subject would, moreover, appear to be essentially necessary at the present period, since the evidence, lately delivered on an extraordinary trial,^[240] has, to a certain extent, very unjustly shaken the public confidence in the tests of chemistry. We shall therefore proceed to consider the processes which are calculated to lead to the detection of Arsenic, in relation to the different circumstances under which it may be presented for investigation, viz. 1, In a solid form; 2, In the simple state of solution; and 3, In the state of combination with various alimentary substances.

1. The Arsenic is in a solid form. This is the most simple case which can occur, and the experiments by 233which its presence is to be demonstrated, will constitute the basis of the inquiry, which we shall be hereafter called upon to institute, for the detection of the same substance under other circumstances of mixture and combination.

The order of succession to be observed in the different experiments which we are about to describe, must, in a great measure, be regulated by the quantity of the material to be submitted to examination. Should it be small, it will be prudent to reserve the process of metallization, by which a considerable loss must necessarily arise, until we have submitted it to the various re-agents which are calculated to afford indications of its nature. If, on the contrary, the quantity of the substance exceed two or three grains, it will be adviseable to proceed in its examination by the following processes, reserving a portion for future analysis.

A. By its reduction to a metallic state. Mix a portion of the suspected substance in powder, with three times its weight of black flux^[241]; put the mixture into a thin glass tube, about eight inches in length, and a quarter of an inch in diameter, and which is hermetically sealed^[242] at one end. Should any of the 234powder adhere to the sides of the tube it must be carefully brushed off with a feather, so that the inner surface of its upper part may be perfectly clean and dry. The closed end of the tube, by way of security, may be thinly coated with a mixture of pipe-clay and sand^[243]; but this operation is not absolutely necessary. The open extremity of the tube is to be loosely plugged with a piece of paper. The coated end must now be submitted to the action of heat, by placing it in a chaffing dish of red hot coals, for ten minutes, or a quarter of an hour; when, if our supposition respecting the nature of the substance has been correct, metallic arsenic will sublime, and be found lining the upper part of the tube with a brilliant metallic crust. The glass tube, when cold, may be separated from its sealed end by the action of a file, which will enable us to collect and examine the metallic sublimate. If a portion of this brilliant matter be laid on heated iron, it will indicate its nature by exhaling in dense fumes, having a powerful smell of garlic. Another portion should be reserved for future experiments.

This method of detecting the presence of Arsenious acid has been considered the most decisive, and indeed the only unexceptionable one, but of this we shall speak hereafter; at present we have only to observe, that it is very far from being a minute test, 235for Dr. Bostock^[244] confesses that where less than three-fourths of a grain were used, he could not say that the metallic crust was clearly perceptible; and Dr. Black^[245] appears to have considered that one grain was the smallest quantity which could be distinctly recognised by such a process.

Chemists were formerly^[246] in the habit of at once projecting any substance, supposed to be Arsenic, on some burning body, in order to develope the alliaceous odour; we have accidentally stumbled upon an instance of this kind, in the fourth volume of the London Medical and Physical Journal, which may serve as an illustration; it is a case communicated by F. Thackeray, Esq. of a child poisoned by arsenic, in which the author says, “the inner surface of the stomach was very red, and was studded throughout with a white powder, which 236when exposed to the flame of a candle, yielded fumes, and a garlic odour was emitted, proving it was arsenic; of which there can be no doubt, as the girl afterwards confessed that she had given arsenic to the infant.”

After the facts we have offered with respect to the alliaceous odour of arsenical fumes, it is only necessary to state, in this place, that such a test, when conducted in the manner just related, must be considered as extremely equivocal.

Another method of identifying “White Arsenic,” by metallization, is to form at the moment of its reduction, an alloy with copper, which may be easily effected in the following manner: Mix the suspected powder with black flux, as in the former experiment, and place the mixture between two polished plates of copper; bind them tightly together by iron wire, and expose them to a low red heat; if the included substance contain arsenic, a silvery white stain will be left on the surface of the copper, which is an alloy of the two metals. In this, as in the former experiment, the presence of an alkali in the flux is essential, since it forms immediately an arsenite of potass, and thereby fixes the arsenious acid, and prevents it from being volatilized before the temperature is sufficiently high to enable the charcoal to decompose it; we therefore differ with Dr. Bostock, when he states that powdered charcoal may be substituted for the black flux.

The property of whitening copper is regarded as a very satisfactory test of the presence of arsenic; but Dr. Bostock has pointed out some circumstances attending it, which we shall here enumerate for the instruction and satisfaction of the less experienced operator. “It may be necessary,” says he, “in the first 237place, to describe the phenomena that take place when copper is heated according to the process that is described above, but without the addition of the arsenic. Two copper disks, of nearly an inch and a half in diameter, scoured bright with sand, had one grain of powdered charcoal, made into a paste with oil, placed between them; they were bound together with an iron wire, and then kept red hot for ten minutes. When they were withdrawn from the fire, the metal was found to have lost its former appearance, and to have acquired the dull white colour of lead or zinc; the insides of the disks were found to present the same whitish appearance, except on the spot where the charcoal was placed, a small part of which still remained unconsumed. As the disks cooled the whitish matter which covered them began to separate, and fly off with some force, in the form of small scales, leaving a clean surface of the proper copper colour. The charcoal was rubbed off, and the surface below it was found smooth and polished; it had acquired a light colour, resembling that of brass; and, near the centre, there was a small spot, which approached to a steel grey. This appearance still continued, after it had been rubbed with fine sand. The above description,” concludes Dr. Bostock, “will probably impress the Society^[247] with the same idea, that, I confess, it gave to myself, that if I had performed this experiment upon a substance, which had been suspected to contain arsenic, and I had not been aware of the appearance that I was to meet with, I should have conceived that I had detected its presence. Upon repeating the process, in precisely a similar manner, except that one grain of 238arsenic was added to the charcoal, the oxidation of the copper took place as before, and a small part of the charcoal remained unconsumed; but upon rubbing it, the white stain was perfectly visible. However, when these disks were compared with those in which the former experiment had been made, the difference between them seemed more in degree than in kind; so that I should not choose to decide upon the presence of arsenic, as indicated by this test, unless the result were more obvious than we can ever expect to find it, where the quantity of arsenic is so small. It may be proper to observe, that copper, whitened in this manner by arsenic, is very subject to tarnish; in three days I could with difficulty distinguish which of the disks had been employed in these two experiments.”

In connection with the different modes of identifying arsenic by metallization, we may relate a test lately proposed by Mr. A. Thomson, which, as a collateral proof, merits some attention. “Into any solution, in which arsenic may be suspected, stir a moderate quantity of charcoal powder; allow it to settle; then pour off the clear supernatant liquor, or filter the mixture; and when the powder which remains on the filter is dry, sprinkle some of it on a red hot poker; if the solution contain arsenic, the odour of garlic will be rendered sensible. This effect becomes more obvious if a few grains of dry sub-carbonate of potass be added to the dried charcoal powder.”^[248]

If, instead of Black flux, or charcoal, the arsenious acid be heated in a glass tube with quick-lime, a sudden ignition will take place, when one part of the 239white arsenic will be metallized, and the other farther acidified, so as to produce an arseniate of lime; in this case, therefore, a certain portion of the arsenious acid is robbed of its oxygen to complete the acidification of the rest.

The habitudes of arsenious acid with the nitrates, as first observed by Kunkel, deserve also some attention. If they be heated together, the former will be oxygenated at the expense of the nitric acid, nitrous acid vapour will be disengaged, and an arseniate of potass remain. The forensic chemist may avail himself of these facts, and obtain a very useful test, which may be applied in the following manner.^[249] Take a grain or two of the suspected powder, and mix it with double the quantity of Nitrate of Potass; introduce this mixture in a small glass tube, and apply the flame of a spirit lamp under the powder; when, if it contain arsenic, the nitrate will be decomposed, nitric oxide and nitrous acid be evolved in a gaseous form, and an arseniate of potass remain.

The acid vapour may be easily recognised by its colour and smell, or by placing a piece of moistened litmus paper within the tube. The arseniate may be identified by the brick-red precipitate, produced in its solution, by Nitrate of Silver. So small is the quantity of arsenic required for this latter mode of trial, that Mr. Smithson, in a late paper, observes “that a drop of a solution of arsenious acid in water, which at the height of 54·5 Fah. contains not more than 1/80th of the acid, put to nitrate of potass in a platina spoon, and fused, affords a considerable quantity of arseniate of silver. Hence when no solid particle 240of oxide of arsenic can be obtained, the presence of it may be established by infusing in water the matters which contain it.”^[250]

B. By the application of certain re-agents, or tests, to its solutions.

a. Fused Nitrate of Silver, or Lunar Caustic. For this test we are indebted to Mr. Hume, who first suggested its application in the Philosophical Magazine for May 1809, (vol. xxxiii). His method of using it is as follows: into a clean Florence flask introduce two or three grains of the suspected substance, in the state of powder, to which add about eight ounces of rain or distilled water, and heat the solution until it begins to boil; then while it boils frequently shake the flask, and add to the hot solution a grain or two of sub-carbonate of potass, agitating the whole to make the mixture uniform. Pour into a wine glass about two table spoonsful of the solution, and touch the surface of the fluid with a stick of lunar caustic. If arsenic be present, a beautiful yellow precipitate will instantly proceed from the point of contact, and settle towards the bottom of the glass as a flocculent and copious precipitate. By this test the 60th part of a grain may be satisfactorily recognised in two ounces of water. The presence of some alkali is essential to the success of the experiment, since arsenious acid is incapable, by the operation of simple affinity, to decompose the nitrate of silver.^[251] 241The validity of this test has been questioned on several distinct grounds, and which the author has endeavoured to answer in another work^[252]; such, however, is the importance of the question in its judicial consequences, that we shall re-consider it on the present occasion.

Objection 1. The alkaline Phosphates are found to produce precipitates with silver, analogous in colour and appearance to the arsenite of silver. This constituted one of the principal points in the evidence for the defence, on the trial of Donnall for the murder of Mrs. Downing (see Appendix, p. 299), and it must be admitted as a valid objection, if the experiment be performed in the manner just stated; but there are other reagents which will immediately distinguish these bodies, as we shall presently have occasion to state, under the history of the Ammoniuret of silver, as a test for arsenic. The author has also shewn that there is a mode of so modifying the application of the present test, that no error or doubt can arise in the use of it, from the presence of any phosphoric salt. This method consists in conducting the trial on writing paper, instead of in glasses; thus—drop the suspected fluid on a piece of white paper, making with it a broad line; along this line a stick of lunar caustic is to be slowly drawn several times successively, 242when a streak is produced of a colour resembling that known by the name of Indian Yellow; and this is equally produced by the presence of arsenic, and that of an alkaline phosphate, but the one from the former is rough, curdy, and flocculent, as if effected by a crayon, that from the latter is homogeneous and uniform, resembling a water-colour laid smoothly on with a brush; but a more important and distinctive peculiarity soon succeeds, for, in less than two minutes the phosphoric yellow fades into a sad green, and becomes gradually darker, and ultimately quite black; while, on the other hand, the arsenical yellow remains permanent, or nearly so, for some time, when it becomes brown. In performing this experiment the sun-shine should be avoided, or the transitions of colour will take place too rapidly. It would be also prudent for the inexperienced operator to perform a similar experiment on a fluid known to contain arsenic, and on another with a phosphoric salt, as a standard of comparison.

In this way the nitrate of silver, without the intervention of any other test, is capable of removing every ambiguity, and of furnishing a distinguishing mark between the chemical action of arsenic and that of the phosphates. Mr. Hume^[253] states that he has repeated this modification of his experiment with entire satisfaction; and that, in a late unfortunate case of poisoning, he derived considerable information by its application. One of the great advantages of this test is the very small quantity that is required for examination, and which will therefore never prevent our pursuing the subject through the other channels of investigation.

Objection 2. The muriates produce precipitates 243with silver, so copious and flocculent, as to overcome every indication which the presence of arsenic would otherwise afford.

From the general use of common salt, the chemist must be prepared to meet with a muriate in almost every examination after arsenic, besides which this latter substance is occasionally adulterated with the muriate of baryta and by sulphate of lime. Dr. Marcet proposes to obviate the difficulties which the presence of a muriate must occasion, by adding to the fluid to be examined dilute nitric acid, and then cautiously applying the nitrate of silver until all precipitation ceases; in this way the muriatic acid will be entirely removed, while the arsenic, if present, will be retained in solution, and may be afterwards rendered evident by the affusion of ammonia, which will instantly produce the yellow precipitate in its characteristic form. It must, however, be confessed, that this mode appears complicated, and, moreover, requires some chemical address for its accomplishment; it should be also known that the yellow precipitate thus produced is not always permanent, for it is soluble in an excess of ammonia. Under these circumstances, it is surely preferable to precipitate at once from the fluid under examination, all the substances which nitrate of silver can affect, and then to expose the mixed and ambiguous precipitate, so obtained, to a low heat, in a glass tube, when the arsenious acid will be separated by sublimation. In this way the presence of muriates and even phosphates, may, in certain cases, be serviceable, especially if the quantity of arsenic be very minute; for, by increasing the bulk of the precipitate, we shall decrease the difficulty of its examination.

Objection 3. Chromate of potass produces with nitrate of silver a yellow precipitate, which, when placed 244side by side with one produced by arsenious acid, cannot be distinguished by colour or appearance from it. This fact has lately been announced by Dr. Porter, of the University of South Carolina (Silliman’s Journal, iii. 355); but as the presence of Chromate of Potass can never be suspected in any research after arsenic, in cases of forensic interest, it is unnecessary to enter into any details respecting it.

We have stated above, that in consequence of the inability of arsenious acid to decompose nitrate of silver by simple elective attraction, the presence of some alkali becomes indispensable in the examination; and for this purpose Dr. Marcet suggested the superior advantages which would attend the application of ammonia, in all those cases where the arsenic had not been previously combined with a fixed alkali; since the former does not, when added singly, decompose nitrate of silver; a circumstance which, in using the fixed alkalies, is very liable to occasion fallacy. This led Mr. Hume to improve his original plan, by forming at once a compound,^[254] which he calls the Ammoniaco-nitrate of silver, but which may with more propriety be designated, as an ammoniuret of that metal.

b. The Ammoniuret of Silver. This is an improvement of considerable value; for, while it obviates the necessity of ascertaining the exact proportion^[255] of 245alkali required in each experiment, it possesses the desirable property of not in the least disturbing the solution of phosphate of soda.

c. Sulphate of Copper. This test of arsenic is the one discovered by Scheele; when added to the arsenite of potass a beautiful green precipitate (constituting a pigment known by the name of Scheele’s green) is produced; “so decidedly,” says Dr. Bostock, “does this phenomenon indicate the presence of arsenic, that I thought it desirable to ascertain, as exactly as possible, what were the best proportions in which the ingredients should be employed, and in what way they should be mixed, so as to exhibit the effect in the most obvious manner. After a number of trials, in which the substances were employed in various quantities, and under different circumstances, I am disposed to recommend that the proportions of the arsenic, the potass, and the sulphate of copper, should be to each other as the numbers one, three, and five, respectively; for instance, if one grain of arsenic and three grains of potass, be dissolved in two drachms of water; and, in another equal quantity of water, five grains of sulphate be dissolved, we have two solutions, which are transparent, and nearly colourless; but upon mixing them together, the whole is converted into the most beautiful grass-green, from which a copious precipitate of the same hue slowly subsides, leaving the supernatant fluid nearly without colour. If the same materials are employed, in the same manner, but without the arsenic, a delicate sky-blue is formed, which is so decidedly different from the former colour as not to admit of the possibility of error.” In this experiment then, as well as in that with the nitrate of silver, it is necessary that the arsenious acid should be combined with an alkaline 246base; and for the same reason, in order to bring the double elective attractions into play; Mr. Hume has accordingly availed himself of the property of ammonia, to form an ammoniuret of copper, which is to be made according to the formula already given for the preparation of the silver test.

d. Ammoniuret of Copper. In using this test care must be taken that it be not too highly concentrated, for in that state it will not produce precipitation.

Notwithstanding the confidence with which Dr. Bostock has supported the pretensions of the Sulphate of Copper, as an infallible test for arsenic, its validity has been lately called in question, and it has been stated that a decoction of onions has the property of imparting to the copper precipitate, produced by a fixed alkali, a green colour and appearance completely analogous to that which is occasioned by the presence of arsenic. This opinion was boldly advanced, and supported, on the trial of Donnall, before alluded to, and of which we have given a very ample report in the Appendix. Since this event an opportunity occurred which enabled the author to examine this alleged fact, by a fair and appropriate series of experiments,^[256] the result of which has 247satisfactorily proved that the opinion was grounded on an optical fallacy, arising from the blue precipitate assuming a green colour, in consequence of having been viewed through a yellow medium.^[257] The 248phosphoric salts may also, under similar circumstances, be mistaken for arsenic; for the intense blue colour of the phosphate of copper will, when viewed through a yellow medium, necessarily appear green. Such instances of optical fallacy are by no means uncommon in the history of chemical reagents; thus corrosive sublimate has been said to possess alkaline characters, in consequence of appearing to turn the syrup of violets green, whereas this apparent change is to be solely attributed to the optical combination of the yellow hue of the sublimate with the blue colour of the violet.

Whenever therefore such a source of fallacy can be suspected, the operator would do well to repeat his experiment on white paper, in the manner we have already pointed out, when treating of the silver test; and let it be remembered that the results, when obtained in glasses, should always be examined by day light, and viewed by reflected, and not by transmitted light. Dr. Bostock observes, that a weak solution of the sulphate of copper, without any addition, when held between the eye and the window, frequently presents a greenish tinge. It should be also known that the usual reaction of the ammoniuret of copper, upon a diluted solution of arsenic, is prevented by the presence of tannin; strong tea may therefore render the test inefficient.

e. Sulphuretted hydrogen. This is a very delicate test for arsenic, producing with its solution a beautiful golden coloured liquor, which, after a short time, lets fall a precipitate, and which will take place sooner if a small quantity of acetic acid be added. By this 249re-agent so small a quantity as 1/100000 may be detected in solution. The test, however, is not, says Dr. Bostock, sufficiently discriminative to be depended upon alone; since tartarized antimony and some other bodies, will produce phenomena that may be mistaken for the effects of arsenic. It has, however, the merit of not being affected by tannin, and may therefore be conveniently employed for precipitating arsenious acid, when dissolved in tea.

f. Lime water produces with the solution of arsenic a beautiful white precipitate of arsenite of lime, which easily dissolves in an excess of arsenious acid.

The precipitates occasioned by the foregoing reagents, should be carefully collected, and treated with black flux, in a glass tube, for the purpose of obtaining the metallic sublimate, as above described.

We cannot quit this part of our subject without directing the reader’s attention to the chemical evidence given by Dr. Addington, on the trial of Mary Blandy (see Appendix, p. 241) to prove that arsenic was contained in a powder with which she was supposed to have poisoned her father. To those in the least acquainted with the habitudes of arsenious acid, it must be evident, that no one of the appearances described by Dr. Addington indicates the presence of arsenic;^[258] and his evidence is only to be reconciled upon the supposition that, instead of the arsenic itself, he, in this case, detected the foreign substances with which it had been adulterated; thus it has been before stated that white arsenic, as sold by the druggists, is often adulterated with sulphate of lime; and the decomposition of this substance by the sub-carbonate 250of ammonia (“Spirit of sal-ammoniac”) or by the sub-carbonate of potass (“Lixivium of tartar”) would occasion the precipitation of a white substance, as stated in the evidence; it is however difficult to account for the “considerable precipitation of a lightish coloured substance” by muriatic acid (spirit of salt) by the presence of any impurity likely to be contained in the arsenic, or in the water employed for its solution. If any lime were present, it would probably give “white glittering crystals” of sulphate of lime, by the addition of sulphuric acid (spirits of vitriol). The only plausible evidence of the presence of arsenic in the suspected powder is “the alliaceous smell and white flowers” which Dr. Addington describes as occurring when it was thrown on red hot iron; it must however be confessed, that from the fallacy of the other experiments, it is even impossible to place any confidence in those last mentioned.

Arsenic does not blacken a knife by which it is cut, as stated on the trial of Eliza Fenning; nor does it, when mixed with dough, prevent its rising.^[259]

We have now concluded our history of the different tests which have been proposed for the detection of arsenic. Much has been said and written upon the relative degree of confidence to which they are respectively entitled, and it has been asserted on several occasions, that nothing short of the reproduction of the metal ought to be received by the tribunals of justice, as an unequivocal proof of the presence of arsenious acid. (See Dr. Neale’s Evidence on the trial of Donnall. Appendix, p. 297.) In taking 251an impartial review of all the evidence which the investigation of this subject can furnish, it must appear to the most fastidious, that the Silver and Copper tests, above described, are capable, under proper management and precaution, of furnishing striking and infallible indications; and that in most cases they will be equally conclusive, and in some even more satisfactory in their results, than the metallic reproduction upon which so much stress has been laid; and for this obvious reason, that unless the quantity of metal be considerable, its metallic splendour and appearance is often very ambiguous and questionable. The author is personally acquainted with a case, where the medical person, by no means deficient in chemical address, actually ascribed the presence of arsenic to that which was no other than a film of finely divided charcoal: in this state of doubt the last resource was to ascertain whether it yielded, or not, upon being volatilized, an alliaceous odour. Surely an unprejudiced judge would prefer the evidence of sight, as furnished by the tests, to that of smell, as afforded in the experiment to which we allude; especially after the various fallacies, which we have shewn in the course of the present enquiry, to have occurred with regard to this latter sense. But the question at issue may be easily disposed of to the satisfaction of all parties; for let it be remembered, that the application of chemical reagents on solutions suspected to contain arsenic, so far from throwing any obstacle in the way of the metallic reproduction of that substance, are the very steps which should be adopted as preparatory to the “experimentum crucis.” It is only necessary to collect the precipitates, and to decompose them in the manner already described; and this confirmation of our 252results should never be neglected, for it is the bounden duty of the forensic chemist, who is called upon to decide so important a question as the presence of a corrosive poison, to prosecute by the fullest enquiry every point which admits of the least doubt; he should also remember that in a criminal case, where the life of a human being depends upon his testimony, he has not only to satisfy his own conscience, but that he is bound, as far as he is able, to convince the public mind of the accuracy and truth of his researches.

2. The Arsenious Acid is mixed with various alimentary and other substances.

The detection of the presence of arsenic, amidst a complicated mass of alimentary matter, has long been a problem of interest and difficulty. In the directions which have been already offered for the discovery of arsenic in solution, we have in some measure anticipated several of the resources, of which we are now to avail ourselves. It has been seen how greatly coloured fluids are capable of obscuring, and changing, and even altogether preventing, the arsenical indications. M. Orfila, with an assiduity and accuracy which so eminently characterise all his toxicological labours, has accordingly investigated the peculiar appearances assumed by the arsenical precipitates in different media, such as bile, tea, coffee, wine, broth, jelly, &c. Since the publication of the great work^[260] in which these phenomena are recorded, its author has proposed a new method^[261] of removing its 253difficulties and embarrassments, occasioned by the colouring matter of the above media; which consists in a previous application of Chlorine, so as to change the colour to a shade, that will not offer any optical impediment to the characteristic indications of the tests in question. We are ready to admit that such a mode of proceeding may, on certain occasions, assist the accomplished chemist in his analysis; but in the hands of a person less accustomed to chemical manipulation, we hesitate not to declare that it is subject to fatal fallacies; whereas, by collecting the precipitate, and submitting it to the process of sublimation we shall at once obtain the arsenious acid in a pure form, and be enabled to test it, in distilled water without the chance of error. Why then should we attempt to pursue our game through the windings of a labyrinth, when a direct road lies before us by which we may drive it into the open plain?

We accordingly recommend the juridical chemist, who suspects the presence of arsenious acid in broth, coffee, or any coloured liquid, to add a solution of ammoniuret of silver, and thus to precipitate indiscriminately all the bodies which it may be capable of so affecting. The precipitate may then be collected, and submitted to heat in a glass tube, as before directed.

But the Arsenious acid may perchance be so mixed with various foreign matter as to render its separation by filtration difficult; in such a case, after having boiled it in distilled water, in order to procure all the soluble matter from it, the residual mass may be evaporated to dryness, care being taken that the heat applied for such a purpose never exceeds 250° Fah. or we shall lose the arsenic, should any be present, by volatilization. The residue thus obtained may then be 254submitted to a higher temperature in a subliming vessel, in order to procure the arsenious acid in its pure state. This process applies particularly to the examination of the matter vomited, or the feculent evacuations passed, by the patient. Should the arsenious acid have, in the first instance, been dissolved in oil, Dr. Ure proposes to boil the solution in distilled water, and to separate the oil afterwards by the capillary action of wick threads. If the arsenious acid be mixed with resinous bodies, Oil of Turpentine may be employed as their solvent, which will leave the arsenic untouched. Dr. Black directed the application of alcohol for this purpose, but this is obviously improper, since arsenious acid is soluble in that fluid.

If the physician be called upon to investigate the contents of the alimentary canal after death, and the arsenious acid cannot be discovered amongst the suspected matter, the stomach itself must be cut into small pieces, and in compliance with the directions of Orfila, boiled in ten or twelve times their weight of distilled water, which should be renewed as fast as a portion of it flies off in vapour; this liquor should be cooled and decanted, in order to put a few drops of it into the solutions of the different re-agents which we have before described. If the precipitates should indicate the presence of arsenic, we may proceed according to the directions we have already laid down; if, on the other hand, the fluid offers no indication of poison, the mass exhausted by water should be treated, according to the process suggested by Rose, by boiling it for some time in a solution of potass, by which means the stomach will be partly decomposed and dissolved, and the arsenious acid, with which it might have been combined, saturated by the alkali. In this state the liquor is to be filtered, again boiled, 255and nitric acid added, little by little, until it passes from a dark to a clear yellow colour. The object of the acid in this stage of the process being to decompose and destroy the animal matter. The excess of acid should be saturated with potass, when an Arsenite of Potass will be formed, if there really existed any arsenious acid in the stomach. This M. Orfila recommends us to precipitate by the Hydro-sulphuret of Ammonia, and a few drops of nitric acid; (Rose prefers lime water for the same purpose); a yellow sulphuret of Arsenic will be the result, from which the whole of the metal may be obtained, by drying it upon a filter, mixing it with an equal bulk of potass, and melting it in a small glass tube.

This complicated mode of proceeding will rarely be found necessary; but it should not be neglected, where the presence of arsenic cannot be otherwise detected in the alimentary canal of those who are suspected to have died from its ingestion, especially in the examination of a body where, from the length of time it may have been under ground, there is reason to suppose that the acid exists in a state of intimate combination with the animal matter. And we may take this opportunity to observe, that advanced putrefaction, however disagreeable it may render such researches, will not, in the case of arsenic, defeat their success; let the forensic physician, then, remember, that the length of time which may have elapsed since the death of the body, ought never to be urged as a plea for not having proceeded in its dissection. The task may be personally disagreeable, but it will be less painful than the reflections which must attend a breach of duty; upon such an occasion we would address the anatomist in the quaint but expressive 256words of Teichmeyer^[262], “Præstat enim manus quam conscientiam cruentare et contaminare.”

Arsenic Acid, and its Salts.

It has been stated, that the Metal Arsenic is susceptible of two degrees of oxidizement, the result of its first degree being Arsenious acid, and that of its second Arsenic acid. This latter compound, of which we are now to treat, may be obtained by the repeated distillation of white arsenic with nitric acid. In a solid state it is white, not crystallizable; of a sour, and at the same time, metallic taste; its specific gravity is 3·391; when exposed to the action of heat in a close vessel, it does not become volatile, but melts and vitrifies; thrown on burning coals, it swells, parts with its water, and becomes opaque; if the process of deoxidation be continued, it will, at length, rise in vapours, like those of arsenious acid, and which, like them, will yield an alliaceous odour, or not, according to the circumstances already explained. The Arsenic acid dissolves very readily in water, and is even indeed deliquescent. With alkalies, earths, and oxides, it constitutes a class of salts, called “Arseniates,” all of which, as well as the pure acid, are extremely active poisons; fortunately, however, they are not much employed^[263] in this country, and are not likely to become the instruments of crime. These salts, like those of the arsenious acid, are obedient to the different re-agents 257which were enumerated under the consideration of this latter substance, but with different results; thus the silver test, instead of producing the yellow indication, occasions an equally characteristic precipitate of a red, or brick colour. The ammoniuret, and acetate of copper, furnish a bluish-white precipitate. The arsenic acid, in a solid form, or the arseniate, mixed with black flux, will, like white arsenic, furnish a metallic sublimate, when heated in a glass tube.

The Sulphurets of Arsenic.

There are two Sulphurets of Arsenic: the yellow variety known in commerce under the name of Orpiment, and the red sulphuret, termed Realgar. The bodies, as they occur native, do not appear to be endowed with the virulent powers which distinguish the other compounds of arsenic. M. Renault^[264] gave as much as two drachms of the native orpiment to dogs of different sizes, from which they experienced no inconvenience. Hoffman^[265] also offers his testimony of the inertness of this substance. The same observations apply to the Realgar. It is not a little singular that while these native sulphurets of arsenic should be so harmless, those which are produced by artificial fusions, are extremely virulent in very small doses. M. Renault supposed that this remarkable difference of effect was owing to the arsenic being oxidized in the latter compound, and in its metallic state in the former. This explanation, however, is not considered as satisfactory by M. Orfila, who states that it does not embrace all the varieties 258of the case, for that the sulphuret, which is artificially obtained by pouring the arsenious acid into a solution of sulphuretted hydrogen, is as inert as the native compounds; besides which, chemical analysis has proved that there is no oxygen in any of these sulphurets, and that they only differ from one another, by a greater or less proportion of their two ingredients. This apparent anomaly induced M. Orfila to institute a series of experiments for its investigation, but the results which he has obtained are too unsatisfactory to enable him to decide the question.

The presence of an Arsenical Sulphuret is to be sought for by calcination with caustic potass, in a small glass tube. The sulphuret is decomposed in a few seconds, yielding its sulphur to the potass, while its metallic element is volatilized with the usual phenomena.

Mercury.

Mercury, or Quicksilver^[266], was known in the earliest ages. Its external characters are too familiar to require any particular description in this place. Its specific gravity is 13·568.^[267] In its metallic state it exerts no action on the living system, except that which may depend upon its mechanical properties, although a different opinion has been entertained, (see Pharmacologia, art. Hydrargyrum.)

Several of the combinations of this metal are, however, highly destructive in small doses, and are consequently objects of forensic interest.

259 Corrosive Sublimate.

Oxy-muriate of Mercury. Bi-chloride of Mercury.

This metallic salt is by far the most active of all the mercurial preparations. According to the latest views of Chemistry it is a compound of two proportionals of chlorine, and one proportional of metallic mercury, and is therefore a bi-chloride of Mercury. It generally occurs in the form of a crystalline mass, made up of very small prismatic crystals, which undergo a slight alteration by exposure to air, becoming opaque and pulverulent. Its taste is extremely acrid, with a metallic astringency, occasioning a sensation of obstruction in the throat which continues for some time. Its specific gravity is 5·1398^[268]. When pulverised and thrown upon burning coals, it is immediately volatilized, giving out a thick white smoke, of a very pungent smell, not at all resembling garlic, but which irritates the mucous membranes extremely, and is highly dangerous to those who breathe it. It is soluble in eleven parts of cold, and in three of boiling water; and this solubility may be farther increased by the addition of a few drops of rectified spirit, or of muriatic acid. When swallowed in small quantities it acts as a most virulent poison.^[269]

Symptoms of Poisoning by Corrosive Sublimate.

The effects, as well as the modus operandi, of this salt, will vary with the quantity swallowed. We shall, therefore, first consider the acute symptoms which supervene a dose sufficiently powerful to destroy life in a few hours; and afterwards those which 260may arise from its long continued use in small quantities, and at different intervals.

1. Symptoms which follow a large dose. A most painful burning and sense of constriction is experienced in the fauces; dryness of the mouth and lips; excruciating pain in the stomach and bowels, increased by the slightest pressure, and generally attended with considerable distention; excessive vomiting and purging of frothy mucus; the countenance is frequently red and swollen, and the eyes exhibit a sparkling appearance, accompanied by contraction of the pupils. The pulse is in general quick, small, and hard; suppression of urine takes place, and cold sweats; anxiety; universal pains; convulsions, and death. If the patient survives long enough, a violent ptyalism, and sloughing of the mouth and gums may take place.

2. Symptoms which are produced by the repetition of small doses. In this case the mercurial salt acts as an “Accumulative Poison.” (See page 148). The most striking of the symptoms are those arising from its specific action upon the salivary glands, in consequence of which an increased flow of saliva takes place, the gums become tender and sore, the breath intolerably offensive, and if the use of the salt be not discontinued, the teeth loosen, and even fall out, and their loss is sometimes followed by that of the bones of the palate, or maxillæ; at the same time other evils, although perhaps less apparent, soon arise; the strength and muscular powers of the body begin to fail; emaciation proceeds rapidly; cardialgia, dyspepsia, diarrhæa, and a train of morbid symptoms succeed; violent pains are experienced in the muscles, tendons, or joints; tremors of the limbs, and even paralysis may result; and in some cases, pulmonary 261consumption terminates the existence of the unhappy sufferer. It has been asserted that Corrosive Sublimate, when taken for a long time in small quantities, will sometimes occasion all the symptoms of debility above enumerated, together with hectic fever, without producing salivation. This is a truth which the author’s personal experience will enable him to confirm. The Countess of Soissons, mother of the celebrated Prince Eugene, was accused, at the latter end of the seventeenth century, of having destroyed her husband by these means. A question of considerable importance has arisen, with regard to the specific effects of mercury, which demands some notice in this place. Whether salivation, after having entirely subsided, can ever return without a fresh exhibition of Mercury? Two instances are related by Dr. Mead of the return of salivation, after an interval of several months, when not a particle of mercury had been administered, in any form, during that period.^[270] Dr. Male, in his work on Juridical Medicine,^[271] relates an analogous case which occurred in his own practice: “In March, 1815,” says he, “I gave a small quantity of triturated mercury to a respectable woman in this town, who had been long ill; she became suddenly and unexpectedly salivated. She soon recovered, and enjoyed better health than she had done for a considerable time. In October, without (as she informed me) having taken any medicine whatever, the salivation returned with extreme violence, her mouth sloughed and mortified; and in a few weeks she died.” Dr. Hamilton, the Professor of Midwifery in Edinburgh, relates in his lectures the case of a married lady, who had been 262under the necessity of going through a course of mercury, under the care of the late Mr. Bennet, who, from motives of delicacy did not enquire very minutely into the particular circumstances; but, according to the rule of the day, gave his patient a sore mouth. Four months afterwards she miscarried, and salivation again came on. It was removed for a week, at the end of which it returned, and harrassed her for about twelve months.^[272] The author, in his Pharmacologia,^[273] has cited a case from Hufeland’s Journal, (vol. ix) wherein mercurial influence, after its complete subsidence, had been renewed by doses of opium. In the trial of Miss Butterfield, at the Croydon assizes, for poisoning Mr. Scawen, in the year 1775, the merit of the case entirely hinged upon this question. See vol. 1, p. 303.

Physiological action of Corrosive Sublimate.

When this salt is introduced into the stomach in a large dose, it immediately exerts a corrosive action on that organ, in consequence of which the heart and brain become sympathetically affected, and death results from the suspension of their functions. For this view of the modus operandi of this mercurial salt we are indebted to Mr. Brodie,^[274] whence it would appear that its physiological action is very different from that of arsenious acid; the former acting as a simple escharotic, on the coats of the alimentary canal, 263the latter requiring to be absorbed, before it can display its energies. These observations, however, apply only to those cases in which the quantity of poison has been so considerable as to destroy life in a few hours; where the dose has been small, and the symptoms have arisen from its frequent repetition, the salt produces its effects by a different mode of operation. In this latter case it is absorbed, and carried into the current of the blood, so as to be distributed to every part of the living system; and it has been asserted that, after the long continued and improper use of mercury, it has been discovered in different parts of the body, and even in the brain, in the form of globules. In this way then deleterious effects may arise from the external application of corrosive sublimate, and numerous instances are recorded where such consequences have followed the injudicious use of lotions and plasters, into which it had entered as an ingredient.^[275] In the Medical Repository, for December, 1821, Mr. Sutleffe has communicated the case of a girl of five years of age, who became salivated, and died, in consequence of an application made to the head for tinea capitis, consisting of pomatum rubbed up with a few grains of corrosive sublimate.

Antidotes to Corrosive Sublimate.

After the view which we have taken of the operation of this salt in large doses, it necessarily follows that copious dilution is the very first object which we have to accomplish, and then the ejection of the fluid by vomiting. Sydenham relates an interesting case of poisoning by this substance, which was successfully treated by copious draughts of water, and repeated 264vomiting.^[276] But it becomes a question of great practical importance to enquire, whether there may not exist some counterpoison or antidote which, by decomposing the salt, will at once disarm it of its virulence? This question has been investigated in a very masterly style by Orfila, who has clearly proved by experiment, that neither the alkaline salts and earths, the sulphurets of potass and of lime, nor the martial alkaline tinctures, as proposed by Navier,^[277] deserve the least confidence; for although the salt may by some of these bodies be decomposed, yet the resulting oxide will prove as virulent as the original compound; equally inefficient are the other substances which have been proposed as counter-poisons, such as sulphuretted hydrogen, solutions of sugar,^[278] the infusions of Peruvian bark,^[279] and metallic mercury.^[280]

M. Orfila having observed the facility with which albumen decomposes corrosive sublimate, and gives rise to a triple compound of albumen, muriatic acid, and protoxide of mercury, induced him to ascertain by experiments whether the white of eggs might not 265prove an antidote to that poison; the result of his inquiry has shewn that this is the case; and that by mixing such albuminous matter, in large quantities, with the diluents given to provoke vomiting, the happiest effects may be anticipated. Many examples are recorded of the success of this practice. In the Transactions of the King and Queen’s College of Physicians in Ireland, an interesting case of this kind is related by Dr. Lendrick; it is, however, but justice to state, that there are instances also of the failure of this antidote. In the 41st volume of the London Medical and Physical Journal, p. 204, the reader will find the case of a girl who was poisoned by a drachm of sublimate, and who, notwithstanding the copious administration of albumen, died in ninety hours afterwards.

It has lately been discovered that vegetable gluten, as existing in wheat flour, is capable of producing upon corrosive sublimate the same chemical decomposition, as that which we have stated to arise from the action of albumen; whence the administration of wheat flour and water has been suggested as a ready antidote. On the trial of Michael Whiting, for administering poison (corrosive sublimate) to his brothers-in-law, George and Joseph Langman, the housekeeper, Catharine Carter, stated in evidence, that the flour, (which was subsequently proved to contain corrosive sublimate) could scarcely be made into dumplings with milk^[281]; and another witness, Mrs. 266Hopkins, a neighbour who took charge of the dumpling that had not been boiled, described it as “a comical sort of paste; like glazier’s putty more than paste, though not greasy.” In order to ascertain the correctness of this statement, we mixed powdered sublimate with wheat flour, and proceeded to make it into dough with milk; when the same difficulty as that stated by the above witnesses, embarrassed the process, and satisfied us of the truth of their testimony. The phenomenon would appear to depend upon the mutual chemical changes which arise in the gluten and mercurial salt.

Organic Lesions discovered on Dissection.

The œsophagus and stomach will be found inflamed, and sometimes eroded, as in poisoning by arsenic. Salin has asserted, that this salt never produces perforation of the intestinal tube; this, however, is not the fact; and we know not of any exclusive appearances, by which the organic lesions inflicted by this poison can be distinguished, unless indeed it be the black appearance of the stomach, as if it had been burnt, which occasionally presents itself.

267 Of the Chemical Processes by which the presence of Corrosive Sublimate may be detected.

As the chemist, devoted to forensic enquiry, will be required to identify this substance under very different states of mixture and combination, we shall proceed to enumerate the various obstacles that may possibly oppose his researches; and, at the same time, to suggest the expedients by which they may be successfully evaded. Unlike arsenious acid, corrosive sublimate is so readily decomposed by various alimentary substances, that, when we attempt to demonstrate its presence in such mixtures, we shall be more frequently compelled to rest our proof upon the products of the analysis, than upon the actual reproduction of the salt.

We shall proceed to consider the best modes of establishing the presence of this salt, in the different forms in which it may occur, viz. 1, In the solid form; 2, Dissolved in water or spirit; 3, In various coloured liquids; 4, In a state of mixture with various solids; 5, Combined with solid or liquid aliments, by which it undergoes decomposition; 6, In a state of combination with the textures of the alimentary canal.

1. The sublimate is in its solid form. The external characters by which this salt is distinguished will go far to establish its identity; but the fact should always receive the support of a chemical proof; and as this is to be derived from the phenomena afforded by its solutions through the intervention of various tests, it will meet with full consideration in the following section, viz.

2. The salt is in the state of solution, in water, or spirit. Let us then suppose that we have a solution of some body in distilled water, which we suspect to 268be corrosive sublimate, by what means are we able to identify it?

(a) By its metallization, through the agency of galvanism. We are indebted to Mr. Sylvester for first suggesting the mode by which galvanic electricity might be applied for the detection of minute quantities of corrosive sublimate in solution. His method is as follows. A piece of zinc or iron wire, about three inches in length, is to be twice bent at right angles, so as to resemble the greek letter π, the two legs of this figure should be distant about the diameter of a common wedding ring from each other, and the two ends of the bent wire must afterwards be tied to a ring of this description. Let a plate of glass, not less than three inches square, be laid as nearly horizontal as possible, and on one side drop some sulphuric acid, diluted with about six times its weight of water, till it spreads to the size of a halfpenny. At a little distance from this, towards the other side, next drop some of the solution supposed to contain corrosive sublimate, till the edges of the two liquids become joined; and let the wire and ring, prepared as above, be laid in such a way, that the wire may touch the acid, while the gold ring is in contact with the suspected liquid. If the minutest quantity of corrosive sublimate be present, the ring, in a few minutes, will be covered with metallic mercury on the part which touched the fluid.

The above experiment may be beautifully simplified in the following manner^[282]. Drop a small quantity 269of a solution, supposed to contain the salt in question, on a piece of gold, and bring into contact a key, or some piece of iron, so as to form a galvanic circuit; when, if sublimate be present, the gold will immediately be whitened.

A solution of nitrate of silver will, under similar treatment, occasion on gold a white precipitate; but as no amalgamation takes place, it is readily wiped off, and cannot therefore occasion any fallacy.

(b) By precipitating metallic mercury from its solution, by the contact of a single metal. It should be generally known that, by virtue of superior affinity, certain metals will decompose the solution of corrosive sublimate, with different phenomena; in those cases where the precipitating metal is capable of forming a direct union with mercury, we shall find the precipitates to consist of an amalgam of the metal employed; where no such combination takes place, the mercury may be frequently seen standing on the surface as a metallic dew. This is particularly striking when iron or steel has been employed. In the evidence given on the trial of Mary Bateman^[283], 270better known by the name of the “Yorkshire Witch,” Mr. Thomas Chorley, surgeon at Leeds, stated that he had received from his assistant, Mr. Hammerton, a jar which he had carefully preserved in his possession, and of the contents of which he gave the following account. “Upon tasting a portion, it was very acrid, styptic, and permanent upon the tongue; I then took a small quantity of it upon a clean knife, and rubbed it with my finger; a change of colour immediately appeared; further rubbing produced numerous globules of quicksilver, and the knife was, at the same time, blackened by it; this change of colour led me to suspect that it must be a mercurial composition, and having made a solution of it, and subjected it to a series of tests and experiments, it is my opinion, that the mixture in the pot did contain honey, and corrosive sublimate of mercury. In order, however, more fully to satisfy myself upon this point, a mixture was made of these ingredients, when it was found to yield the same results.” In the above experiment, the steel knife decomposed the sublimate, forming a chloride of iron, while the mercury, thus disengaged in its metallic form, being unable to amalgamate with the iron, appeared in globules^[284] upon 271its surface. At the same time the knife became blackened owing to the precipitation of carbonaceous matter from the steel.

(c) Carbonate of Potass. A saturated solution of this salt, added to that of corrosive sublimate, will produce a deep brick coloured sediment, which is stated to consist of per-carbonate of mercury^[285]; while a muriate of potass will be found to remain in solution. The sub-carbonate of potass will occasion a somewhat different precipitate, of a clear brick colour, and consisting of a mixture of the carbonate, and oxide of the metal.^[286]

(d) Ammonia. A solution of the volatile alkali produces a white precipitate, which is an insoluble triple salt, composed of muriatic acid, ammonia, and oxide of mercury; being heated it grows yellow; it passes afterwards to red, and according to Orfila gives out ammoniacal gas, nitrogen, calomel, and metallic mercury. In this operation the oxide of mercury is supposed to be deoxidized by the hydrogen which results from a portion of the decomposed ammonia.

(e) Lime water. This reagent may be said to decompose corrosive sublimate more perfectly than any alkaline body; occasioning a precipitate of a deep yellow colour, which will be found to be a peroxide of mercury; unless indeed the quantity of lime water be very small, when it will be a sub-muriate of the peroxide.

272(f) Nitrate of Tin. According to Dr. Bostock^[287] this test is capable of detecting the three-millionth part of a grain in solution. A single drop will produce an immediate and copious dark-brown precipitation.

All the above precipitates, if rubbed on a bright plate of copper, will render its surface silvery white, in consequence of the amalgamation which takes place.

Brugnatelli has lately proposed a method of distinguishing corrosive sublimate from arsenic, which we have repeated to our satisfaction; but the experiment requires some nicety of manipulation to secure its success. Take a quantity of fresh wheat starch, mix with water, and add a sufficient quantity of iodine to give the liquid a blue colour; if either of the above poisons be now introduced into it, the colour will be destroyed, and assume a reddish tint; but if the change has been effected by the latter substance, a few drops of sulphuric acid will restore the blue colour; whereas if it has been produced by the former, it is not recoverable by such means.^[288]