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DETECTION OF POISONS.
ON THE DETECTION OF ARSENIC.
8 1. ARSENIO belongs to the class of irritant poisons. Of all the members of this group, which embraces the compounds of the metals, it is for the medical jurist the most important. Arsenic and its compounds are more frequently chosen for the purpose of committing both suicide and murder than any other poison. Out of 543 cases of fatal poisoning, brought before the coroners of England, during the years 1837 and 1838, 186 were due to arsenic.—(Christison.) In France, 616 accusations for poisoning were brought before the courts, from 1826 to 1845; of these nearly two-thirds were for poisoning with arsenic; for the years 1841 to 1844 the total number of cases was 201 ; 137 out of which were for poisoning with arsenic.(Flandin.)
The most usual shape in which this poison is administered is in that of arsenious acid, or white arsenic. But cases of poisoning with fly-powder, with arsenite of copper, arsenite of potassa, arsenic acid, the various sulphides of arsenic, and other compounds are, also, of frequent occurrence. In whatever form the arsenic may have been given, the general analytical process is the same; and it is only in case particles of the poison should be detected unchanged in the stomach or the intestines, that the performance of some special reactions might be required. These are fully described below (8 4 to 7), for the most frequently occurring compounds.
$ 2. The first thing in beginning a legal analysis is, to convince one's self that the re-agents are perfectly free from arsenic. The barest possibility of this not being the case is sufficient to make a thorough examination, and, if required, purification necessary.*
* The purity of the hydrochloric acid which, in the process for the detection of arsenic and the metals in general, is often used in considerable quantities (several pounds being sometimes required), should more especially be attended to. The acid should be treated with sulphureted hydrogen, for there is no other way to remove those traces of arsenic which are, perhaps, never wanting, but which become only evident in operating on large quantities. Four pounds of crude hydrochloric acid, which I use in my laboratory, for the preparation of pure acid, and which passes generally for being free from arsenic, afforded, on being diluted with an equal volume of water, and treated with sulphureted hydrogen, a deposit in which the presence of arsenic could be distinctly shown by Marsh's test. For the purpose of legal investigations it is very convenient to keep on hand a quantity of acid that has been purified by sulphureted hydrogen; it is sufficiently concentrated.
[Zinc and sulphuric acid frequently contain arsenic, sometimes in
The fact of these operations having been performed should be mentioned in the report (see below).
§ 3. In considering the process followed in the chemical examination, it is most convenient to assume three different cases, as pointed out by Wöhler:
I. The arsenious acid is found in the solid state in the contents of the stomach and intestines, or in the vomited matters.
II. The poison is intimately and invisibly mixed with, or dissolved in, the contents, etc., and can, therefore, no longer be found or separated by mechanical means, in the solid state.
III. The stomach and intestines are empty, or no arsenic can be detected in them, since it has already
considerable quantity. Zinc is scarcely ever free of a trace of arsenic, but I never experienced any difficulty in obtaining zinc so pure as to exhibit not a trace of arsenic, by Marsh's method. Jacquelain could not detect an atom in any French specimen of zinc, or its car. bonate or silicated oxide, as met with in commerce.- —(Journal de Chimie méd. 1842.) Brett satisfied himself that no British or foreign zinc he could obtain indicated the presence of arsenic by a process capable of detecting one 5000th of that metal in zinc. (London Philosophical Journal, 1842.) Schäuffele found in one kilogramme of French zinc.
0.00426 gram arsenic. Silesian zinc
0.00097 Zinc of Vielle-Montagne . 0.00062 Zinc of Corfali
0.00005 (Journ. de Chimie méd. 3 Sér. T. VI).
The amount of arsenic in common sulphuric acid is often very great. Cameron found about an ounce of crystallized arsenious acid deposited, after long standing, from eight pounds of sulphuric acid. (Chem. Gazette, 1856.) The acid sold as pure, in commerce, I found, by my experiments, to be sufficiently free from arsenic to be be used in Margh's process. In g 18 the method of testing zinc and sulphuric acid for its purity is described.]
been absorbed into the mass of the blood, or into the substance of the different organs.
The most characteristic reactions by which arsenious acid may be recognized, will be given below; and the question, “Is the substance under examination white arsenic ?” is easily answered, when the poison is found in the solid state. But, if poisoned food, or contents of the stomach, etc., or vomited matters, blood, urine, or entire organs, ex. gr., liver, spleen, are to be examined, it becomes much more difficult, owing to the presence of organic matter and foreign salts, which cause several of the reactions to become indistinct; and it is for such cases, principally, that the various methods for the detection of arsenic, in legal investigations, are given. In such cases particular attention should be paid to the resemblance of antimony and arsenic, because tartar emetic is frequently administered to produce vomiting when poisoning is suspected.
The famous trial of Madame Lafarge has given occasion to à careful revision, within the last few years, of all the various methods for the detection of arsenic. The result of this revision has led to the conclusion, that the experienced and careful chemist can attain his end by various ways with equal certainty. But it is only the experienced and careful chemist, and no other person, who should be trusted with a legal investigation of this kind; for it is not sufficient that a man knows how the thing is done, he should also be able to do it, and that on the most approved principles, and with experienced hands. In many cases, the detection of arsenic is a very easy matter; but, if the poison exists in very minute quantities, it is only with a great deal of care and circumspection that the analyst will be able to prove its presence conclusively. To make the examination as much as possible independent of the individual qualifications and amount of chemical knowledge of the analyst, is the principal object of these pages. They are not intended for the chemist by profession, and to him they are only in so far of value as they contain a compilation of all that has been published on the subject.*
$ 4. White arsenic being but with difficulty solublet
* The literary material on this subject is considerable. Among the recent publications the more important ones are the following:
Das forensisch-gerichtliche Verfahren bei einer Arsenikvergiftung, von F. Wöhler und E. v. Siebold. Berlin, 1847; a very excellent pamphlet. Über ein neues Verfahren zur Ausmittelung und quantitativen Bestimmung des Arsens bei Vergiftungsfällen, von Dr. R. Fresenius und Dr. L. v. Babo (Annalen der Chemie und Pharm. Bd 49 p. 287). Das Arsenik, seine Erkennung, etc , von Duflos und Hirsch, Breslau 1842. Hand-book of inorganic analysis, by F. Wôhler; edited by A. W. Hofmann, London 1854; and the treatises on analytical chemistry, by H. Rose, R. Fresenius, etc. A treatise on poisons, by R. Christison, M. D.; American edition, Phil. 1845. Traité des poisons, par Ch. Flandin. Vol. I. Paris 1846. Traité de Toxicologie, par M. Orfila. 5 ed. Paris 1852. Die gerichtliche Chemie, von F. C. Schneider. Wien 1852; and the different works on medical jurisprudence.
[f The solubility of arsenious acid is a point of some medico-legal importance. It is different in the two modifications in which this acid occurs. According to Guibourt
100 parts of water contain:
of the opaque
Of the transparent
Solution saturated at 15° 0.
cooling and resting for 2 days,
Alfred Taylor observed that water, boiling gently for an hour, dis.