Oxydum Arsenici. E. Arsenicum. D. _White Arsenic_.
_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.