OF POISONING WITH OXALIC ACID.
The last poison of this order is oxalic acid. It is a substance of very
great interest; for it is a poison of great energy, and in this country
is in common use for committing suicide, and has been often taken by
accident for Epsom salt.
It is certainly ill adapted for the purposes of the murderer; for
although it might be easily given to a sick person instead of a laxative
salt, yet its real nature would betray itself too soon and too
unequivocally for the chief object of the prisoner,—secrecy.
Nevertheless, attempts of the kind have been made. At the trial of James
Brown for assaulting his wife, held at the Middlesex Autumn Assizes
1827, it was brought out in evidence that he had previously tried to
poison her by giving her oxalic acid in gin;[386] and Mr. Alfred Taylor
says he is acquainted with two similar cases, where an attempt was made
to administer it in tea.[387]
It was first made known as a poison by Mr. Royston in 1814.[388] Its
properties have been examined by Dr. A. T. Thomson of London,[389] and
Dr. Perey of Lausanne;[390] in 1823, the whole subject of poisoning with
oxalic acid in its medico-legal relations was examined by Dr. Coindet of
Geneva and myself;[391] and in 1828, another experimental inquiry, which
confirms most of the results we obtained, was published by Dr. Pommer of
Heilbronn.[392]
SECTION I.—_Of the Tests for Oxalic Acid._
Oxalic acid is commonly in small crystals of the form of flattened
six-sided striated prisms, transparent, colourless, free of odour, very
acid to the taste, and permanent in the air. Two other common vegetable
acids, the citric and tartaric acids, present a totally different
crystalline form. In general appearance it greatly resembles the
sulphate of magnesia, for which it has been so often and so fatally
mistaken. So close, indeed, is the resemblance, that repeatedly, on
desiring several persons to point out which was the poison and which the
laxative, I have found as many fix on the wrong as on the right parcel.
The sulphate of magnesia has of course a very different taste, being
strongly bitter. Various plans have been devised for preventing the
accident to which this unlucky resemblance has given rise. The best of
them imply the use of a safeguard by the patient before he takes his
laxative draught. It seems to have escaped the notice of those who have
proposed the plans in question, that, if accidents are to be prevented
in this manner, by far the simplest and most effectual security will be
to let the public know, that a laxative salt ought always to be tasted
before being swallowed. Its solubility has been much overrated by some
chemists. It does not appear to me soluble in less than eleven parts of
water.
In determining the medico-legal tests for oxalic acid, it will be
sufficient to consider it in two states,—dissolved in water,—and mixed
with the contents of the stomach and intestines or vomited matter. If
the substance submitted to examination is in the solid state, the first
step is to convert it into a solution.