Arsenious Acid. vulgo Arsenic.
Qualities. Form, shining semivitreous lumps, breaking with a conchoidal fracture, and when reduced to powder, bearing some resemblance to white sugar; Taste, acrid and corrosive, but not in any degree corresponding with its virulence, leaving an impression of sweetness. Specific gravity 3·7; it is volatilized at the temperature of 383° Fah: and by a strong heat is vitrified into a transparent glass capable of crystallizing in tetrahedra with truncated angles, or rather in octohedra. In the state of vapour it is quite inodorous, although it is asserted in many chemical works of authority to yield 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 acid seems to yield this odour, we may infer that its decomposition has taken place; this happens when it is projected upon ignited charcoal, or when heated in contact with those metallic bodies which readily unite with oxygen, as Antimony and Tin. It is stated by Orfila and other chemists, 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 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; for I find by experiment that if a few grains of this substance be heated on a plate of copper, by means of a spirit lamp or blow-pipe, no odour is perceptible, for the whole of the acid is dissipated before the copper can acquire a sufficiently exalted temperature to deoxidize it. If the arsenious acid be heated on a plate of zinc, the smell is not evolved until the metal is in the state of fusion; if instead of these metals we employ in our experiments those of gold, silver, or platinum, no alliaceous smell whatever is produced, at any temperature. It however deserves particular notice, that the flame of the spirit lamp is itself capable of decomposing the oxyd, in consequence of the operation of its hydrogen: a fact which is very likely to betray the chemist into the fallacious belief that the oxyd does yield the odour in question.[[399]] It is probable that arsenical vapours which yield this peculiar odour are less noxious than those which are inodorous, but I am not aware that the knowledge of this fact can be applied to any purpose of practical importance.[[400]] Chemical Composition. This substance possesses many of the essential habitudes of an acid, as for instance, that of combining with the pure alkalies to saturation; it is therefore very properly denominated Arsenious Acid. It may be farther acidified by distilling it with nitrous acid, and the compound which results is a white concrete substance termed Arsenic Acid; from experiments on the quantity of oxygen absorbed by metallic arsenic, during its conversion into these two compounds, instituted by Proust and Davy, it appears that the arsenious acid consists of about 25 of oxygen and 75 of metal, and the arsenic acid of 33 of oxygen and 67 of metal; or, the quantity of metal being the same, that the oxygen in the latter compound is to that in the former nearly as three to two. Solubility. We have but lately been set right upon this point; Klaproth has shewn that it requires for its solution 400 parts of water at 60° and only 13 at 212°, and moreover, that if 100 parts of water be boiled on the arsenious acid, and suffered to cool, it will retain three grains in solution, and deposit the remainder in tetrahedral crystals; this fact shews the importance of employing boiling water in every chemical examination of substances supposed to contain arsenic. It is soluble in alcohol and oils, the former taking up two per cent.; with lime water it produces a white precipitate of arsenite of lime, which is soluble in an excess of arsenious acid; with magnesia it forms a soluble arsenite, which proves very virulent. The poisonous effects of arsenious acid are so amply detailed in medical works,[[401]] that it would be superfluous to dwell upon them in this place; it may however be interesting and useful to record an account of the pernicious influence of arsenical fumes upon organized beings, as I have been enabled to ascertain in the copper smelting works, and tin burning-houses of Cornwall. This influence is very apparent in the condition both of the animals and vegetables in the vicinity; horses and cows commonly lose their hoofs, and the latter are often to be seen in the neighbouring pastures crawling on their knees, and not unfrequently suffering from a cancerous affection in their rumps, whilst the milch cows, in addition to these miseries, are soon deprived of their milk; the men employed in the works are more healthy than we could a priori have supposed possible; the antidote upon which they all rely with confidence, whenever they are infested with more than an ordinary portion of arsenical vapour, is sweet oil, and an annual sum is allowed by the proprietors in order that it may be constantly supplied; this opinion is not solitary, for Tachenius relates that the poisonous effects, such as convulsions, gripes, and bloody stools, with which he was seized from exposure to the fumes of arsenic, were relieved by milk and oil.
It deserves notice that the smelters are occasionally affected with a cancerous disease in the scrotum, similar to that which infests chimney-sweepers, and it is singular that Stahl in describing the putrescent tendency in the bodies of those who die from this poison, mentions in particular the gangrenous appearance of these parts. It is a very extraordinary fact that previous to the establishment of the copper works in Cornwall, the marshes in their vicinity were continually exciting intermittent fever, whereas since that period a case of ague has not occurred in the neighbourhood; I have heard it remarked by the men in the works, that the smoke kills all fevers. The fact is here stated without any other comment than that the agricultural improvements which have taken place in the district, are not sufficient to afford any clue to the explanation of the circumstance. Medicinal Uses. Much has been said upon this subject, and the propriety and safety of its exhibition has been often questioned; there can be no doubt but that the greatest circumspection is required in the practitioner who administers it, and it ought not, in my opinion, to be employed until other remedies have failed; that it is capable of accumulating in the system is very evident, and this, in certain habits, may predispose the patient to serious diseases; the form in which it is most manageable and least dangerous, is that of solution. See Liquor Arsenicalis. Some practitioners have exhibited it in substance, made into pills, by rubbing one grain with ten of sugar, and then beating the mixture with a sufficient quantity of crumb of bread to form ten pills, one of which is a dose. The Chinese and other oriental nations form the sulphuret of arsenic (realgar) into medical cups, and use lemon juice, after it has stood some hours in them, by way of cathartic. As an external application, arsenic has long been extolled in the cure of cancers; the caustic so extensively used under the sanction of the late Mr. Justamond in cases of open cancer, consisted of two parts of Antimony, and one of Arsenious acid, fluxed together in a crucible, and afterwards levigated, and reduced to the requisite degree of mildness by the addition of powdered Opium.[[402]] But it deserves notice in this place, that repeated experiments have proved that arsenic kills[[403]] more rapidly when applied externally to an abraded part, than when internally administered. See page 132. 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 (Epist. 168.) observed an ulcer of the breast produced by them. Vernascha, violent pains and syncope. Amongst the foreign authors who have related cases of poisoning by the external application of Arsenic we may mention Desgranges (Recueil Period: de la Société de Med: de Paris, T. vi. p. 22.) who records the history of a chambermaid, poisoned by having rubbed her head with an arsenical ointment for the purpose of destroying vermin; and Roux (Nouveaux Elemens de Med: Operat. par. J. P. Roux,) who confessed to have killed a young girl of eighteen by an application of the “Pate Arsenicale” to a cancerous breast. To the Empirics of our own times we are indebted for many fatal illustrations of the subject. Since the last edition of this work, a Lady applied to a well known Quack, distinguished for his impudent pretensions in the treatment of cancer, and submitted to a caustic application to the breast. In a short time paralysis ensued, and the application was discovered to contain a large proportion of Arsenic, and that the disease, for the cure of which it had been applied, was not cancer. A somewhat analogous case occurred under the care of a bold empiric in the neighbourhood of St. George’s Fields, who undertook to remove the deformity of bow legs in a dandy drawing-master! by rasping the shin bones, and applying arsenic to the surface of the wound; in consequence of which, in addition to extensive local mischief, the unhappy dupe became paralytic. It is also necessary to inform the practitioner that Arsenious acid has been known to produce poisonous effects when applied to the unbroken skin; a case of this nature is related by Desgranges, in the sixth volume of the Recueil Periodique de la Soc: de Med: another may be found in the 22d volume of the Acta Germanica (1730); and Renault obtained similar results in his experiments on animals. When the system is under the influence of arsenic, the following symptoms will appear, viz. thickness, redness, and stiffness of the palpebræ, soreness of the gums, ptyalism, itching over the surface of the body, restlessness, cough, pain in the stomach and bowels, head-ache, and I have also occasionally noticed paucity of urine, and even stranguary, a fact of which I find no mention in other authors. Strange as it may appear, Arsenic has been inhaled, together with the vapours of frankincense, myrrh, and those of other gums during a paroxysm of asthma! This extraordinary practice arose from the practitioner mistaking the gum juniper, or Vernix of the Arabians, which by their medical authors was prescribed in fumigations under the name of Sandarach, for the Σανδαρακη of Aristotle, which was a sulphured of arsenic.
Adulterations. It is frequently sophisticated with chalk, gypsum, or sulphate of barytes; the fraud is instantly detected by its not being entirely volatilized by heat, or by any insoluble residuum occurring in preparing the Liquor Arsenicalis, according to the directions of the pharmacopœia. To many the adulteration of so active a substance may seem unimportant, but in consequence of its being thus rendered a medicine of variable activity, it is one of the most dangerous frauds which can be committed; a very unpleasant circumstance lately occurred from such a cause in one of our public institutions: arsenic had been obtained from the shop of a respectable chemist, who had not usually supplied the establishment, for the purpose of preparing the arsenical solution: the article happened to be less adulterated than that which had been previously employed; the solution however was prepared in the usual way, and the usual dose was continued, when the patients were soon seized with violent pains in the bowels, and the cause was not detected until by an examination of the bottle the usual sediment was not discovered.
Antidotes. Late researches have shewn that sulphuret of potass, on which physicians have placed so much reliance, merits no confidence. The great indication to be fulfilled in all cases of poisoning is to excite vomiting, and to administer liquids which are the least liable to act as solvents of the acrid matter, on which account lime water presents itself as a very appropriate fluid. The subject, however, is very fully considered in the first part of this work, to which I am very desirous of directing the attention of the medical practitioner; see Antidotes.
Methods of detecting the presence of Arsenious Acid.
1. By its reduction to a metallic state. Mix a portion of the suspected powder with three times its weight of black flux;[[404]] put the mixture into a thin glass tube, hermetically closed[[405]] at one end, about eight inches in length, and one-fourth of an inch in diameter; should any of the powder 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,[[406]] but this operation is not absolutely necessary; the open extremity is to be loosely plugged with a piece of paper; the coated end must be now heated on a chaffing dish of red hot coals, when the arsenic, if present, will sublime, and be found lining with a brilliant metallic crust the upper part of the tube; a portion of this reduced metal, if it be arsenic, will, when laid on heated iron, exhale in dense fumes, which are characterised by a strong smell of garlic. Mr. Phillips has lately stated that the tube may be sufficiently heated, for the purpose of metallization, by means of a spirit lamp.[[407]]
It merits particular notice, that in reducing by the above process the arsenious acid to the state of metal, the presence of potass in the flux is very 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; an ignorance of this fact has not unfrequently proved a source of disappointment and fallacy.
Another method of identifying white arsenic by metallization, is to form at the moment of its reduction, an alloy with copper, which is 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 tight together by iron wire, and expose them to a low read heat; if the included substance contained arsenic, a silvery white stain will be left on the surface of the copper, which is an alloy of the two metals. If in this, as in the former experiment, charcoal be employed without the addition of a fixed alkali, the result may, for the same reason, prove unsatisfactory. But, with whatever care this experiment is conducted, it is, to say the least, a clumsy and unsatisfactory test, and ought never to be relied upon.
2. By the application of certain Reagents, or Tests, to its Solutions.