Treatise on Poisons by Sir Robert Christison
6. _The Sulphurets of Arsenic._
1303 words | Chapter 101
In the arts various substances are known which contain a compound of
sulphur and arsenic. In the first place, two pure sulphurets are known
in chemistry and in painting, the one of a fine orange colour, and known
by the name of realgar, the other of a rich sulphur-yellow, and termed
orpiment. Secondly, the name of orpiment is familiarly given to a
pigment in more general use than either of the former, which has a less
lively colour, and consists of pure orpiment with a large admixture of
arsenious acid. Lastly, orpiment also forms a great proportion of
another common pigment, King’s yellow.
The orange-red sulphuret (realgar, risigallum, Σανδαραχη, sandaracha),
is chiefly a natural production. It is solid, of a bright orange-red
colour, and composed of small shining scales, so soft as to be scratched
with the nail. It is composed of one equivalent of metal and one of
sulphur. Its best chemical characters are the disengagement of metallic
arsenic when it is heated in a tube with potass or the black flux; and
its undergoing sublimation unchanged when heated alone in a tube.
The yellow sulphuret (orpiment, auripigmentum, αρσενικον), is both a
natural production, and the result of many chemical operations. The
sulphuret thrown down from solutions of arsenic by sulphuretted-hydrogen
is quite conformable in physical and chemical characters with the
natural orpiment. Natural orpiment, when in mass, consists of broad
scales of much brilliancy and of a rich yellow colour. It is composed of
two equivalents of metal and three of sulphur. Its most striking
chemical characters are the same with those of realgar, from which it is
distinguished chiefly by its colour.
It has been stated by Hahnemann in his elaborate work on Arsenic, that
the pure sulphurets are somewhat soluble in water,—that native orpiment
is soluble in 5000 parts of water with the aid of ebullition, and that
artificial orpiment by precipitation is soluble in 600 parts.[560]
Hahnemann, however, was mistaken in supposing that the water dissolved
these sulphurets. It does not dissolve, but decomposes them. Very lately
M. Decourdemanche has found that, by slow action in cold water, and much
more quickly with the aid of heat, the arsenical sulphuret is decomposed
by virtue of a simultaneous decomposition of the water, hydrosulphuric
acid being evolved and an oxide of arsenic remaining in solution. And he
has farther remarked, that this change is promoted by the presence of
animal and vegetable principles dissolved in water.[561] These facts are
interesting, as they explain certain apparent anomalies to be noticed
presently in the physiological properties of the sulphurets.
The common orpiment of the shops is not a pure sulphuret like the
natural orpiment, but a much more active substance, a mixture of
orpiment and arsenious acid. It is made by subliming in close vessels a
mixture of sulphur and oxide of arsenic. It is met with in the shops in
two forms, in that of a fine powder possessing a yellow colour with a
faint tint of orange, and in that of concave masses composed of layers
of various tints of white, yellow and orange, commonly also lined
internally with tetraedral white pyramidal crystals. Till lately it was
accounted a variety of sulphuret, and some ingenious conjectures were
made as to the cause of its superior energy over the other sulphurets as
a poison. But M. Guibourt has proved that it always contains oxide of
arsenic, and is commonly impregnated with it to a very large amount,
some parcels containing so much as 96 per cent.[562] The inner surface I
have often seen lined with large crystals of pure oxide. In a very
interesting account by Dr. Symonds of Bristol, describing the case of
Mrs. Smith, for whose murder a woman Burdock was executed in that city a
few years ago, it is stated that artificial orpiment was the poison
given, that death took place in a very few hours, and that a sample from
the druggist’s shop where the poison was bought contained on an average
79 per cent. of oxide of arsenic.[563]
Another impure sulphuret, a good deal used in painting, and a favourite
poison in this country for killing flies, is King’s yellow. It is sold
in the form of a light powder or in loose conical cakes. It has an
intense sulphur-yellow colour. This substance is soluble, though not
entirely, in water, both cold and warm, and forms a colourless solution,
from which, on cooling, or by evaporation, a yellow powder separates. In
this respect it differs essentially from the pure sulphurets. The
solution is not acted on by reagents in the same way as the solution of
arsenious acid. Lime-water and hydrosulphuric acid have no effect on it,
the ammoniacal nitrate of silver causes a copious dirty brown, and the
ammoniacal sulphate of copper a scanty, dirty lemon-yellow precipitate.
I have not seen any account of the mode of preparing it or an analysis
of its composition. But according to my own experiments it contains a
large proportion of sulphuret of arsenic, a considerable proportion of
lime, and about 16 per cent. of sulphur. Its nature is best shown by the
following method of analysis. Let the powder be agitated in diluted
ammonia till the colour becomes white. The filtered fluid contains the
sulphuret of arsenic, which, on addition of an acid, falls down, and may
be separated and reduced in a tube with the black flux. The remaining
white powder, well freed from adhering sulphuret by washing, is next to
be agitated in diluted acetate or hydrochloric acid and again filtered.
The solution on being neutralized precipitates abundantly with oxalate
of ammonia and the alkaline carbonates, showing that lime was taken up
by the acid: and, as the acid operates without effervescence, the lime
must have been in the caustic state. The powder which remains after the
action of the acid will be found to fuse with a gentle heat and to burn
almost entirely away with a blue flame, emitting sulphureous vapours.
These experiments make it obvious that King’s yellow contains sulphuret
of arsenic, caustic lime, and free sulphur; and in all probability the
lime exists in the form of a triple sulphuret of lime and arsenic.
All the preparations containing the sulphuret of arsenic are interesting
to the medical jurist, but particularly the two impure sulphurets last
mentioned. The King’s yellow above all should be carefully studied,
because on account of its frequent employment as a fly-poison it has
been the source of fatal accidents. It was likewise taken intentionally
a few years ago in this city, and proved fatal in thirty-six hours. Dr.
Duncan also, while he was Professor of Medical Jurisprudence, met with
an instance of an attempt to poison by mixing King’s yellow with tea;
and at the Glasgow Spring Circuit of 1822 a woman was tried for
poisoning her child with it.
_Process for Organic Mixtures._—If sulphuret of arsenic be present in
such mixtures in appreciable quantity, the particles, owing to their
intense yellow colour, will be visible in any mass which has not the
same tint. From this state of admixture they may be removed by adding
caustic ammonia which dissolves sulphuret of arsenic; and the solution,
on being acidulated with muriatic acid, will deposit the sulphuret
sufficiently pure for undergoing the process of reduction.
Sulphuret of arsenic sometimes exists in small quantity in the stomach,
although the poison was given in the form of oxide; for a portion of the
oxide is subject to be converted into the sulphuret by hydrosulphuric
acid gas evolved in the stomach after death.[564] In every instance of
the kind yet carefully examined a large proportion of the oxide has
remained unacted on, although the intense colour of the mixed sulphuret
makes it appear as if that were the only compound present.
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