Treatise on Poisons by Sir Robert Christison

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.