We cannot quit this part of our subject without directing the reader’s attention to the chemical evidence given by Dr. Addington, on the trial of Mary Blandy (see Appendix, p. 241) to prove that arsenic was contained in a powder with which she was supposed to have poisoned her father. To those in the least acquainted with the habitudes of arsenious acid, it must be evident, that no one of the appearances described by Dr. Addington indicates the presence of arsenic;[[258]] and his evidence is only to be reconciled upon the supposition that, instead of the arsenic itself, he, in this case, detected the foreign substances with which it had been adulterated; thus it has been before stated that white arsenic, as sold by the druggists, is often adulterated with sulphate of lime; and the decomposition of this substance by the sub-carbonate of ammonia (“Spirit of sal-ammoniac”) or by the sub-carbonate of potass (“Lixivium of tartar”) would occasion the precipitation of a white substance, as stated in the evidence; it is however difficult to account for the “considerable precipitation of a lightish coloured substance” by muriatic acid (spirit of salt) by the presence of any impurity likely to be contained in the arsenic, or in the water employed for its solution. If any lime were present, it would probably give “white glittering crystals” of sulphate of lime, by the addition of sulphuric acid (spirits of vitriol). The only plausible evidence of the presence of arsenic in the suspected powder is “the alliaceous smell and white flowers” which Dr. Addington describes as occurring when it was thrown on red hot iron; it must however be confessed, that from the fallacy of the other experiments, it is even impossible to place any confidence in those last mentioned.
Arsenic does not blacken a knife by which it is cut, as stated on the trial of Eliza Fenning; nor does it, when mixed with dough, prevent its rising.[[259]]
We have now concluded our history of the different tests which have been proposed for the detection of arsenic. Much has been said and written upon the relative degree of confidence to which they are respectively entitled, and it has been asserted on several occasions, that nothing short of the reproduction of the metal ought to be received by the tribunals of justice, as an unequivocal proof of the presence of arsenious acid. (See Dr. Neale’s Evidence on the trial of Donnall. Appendix, p. 297.) In taking an impartial review of all the evidence which the investigation of this subject can furnish, it must appear to the most fastidious, that the Silver and Copper tests, above described, are capable, under proper management and precaution, of furnishing striking and infallible indications; and that in most cases they will be equally conclusive, and in some even more satisfactory in their results, than the metallic reproduction upon which so much stress has been laid; and for this obvious reason, that unless the quantity of metal be considerable, its metallic splendour and appearance is often very ambiguous and questionable. The author is personally acquainted with a case, where the medical person, by no means deficient in chemical address, actually ascribed the presence of arsenic to that which was no other than a film of finely divided charcoal: in this state of doubt the last resource was to ascertain whether it yielded, or not, upon being volatilized, an alliaceous odour. Surely an unprejudiced judge would prefer the evidence of sight, as furnished by the tests, to that of smell, as afforded in the experiment to which we allude; especially after the various fallacies, which we have shewn in the course of the present enquiry, to have occurred with regard to this latter sense. But the question at issue may be easily disposed of to the satisfaction of all parties; for let it be remembered, that the application of chemical reagents on solutions suspected to contain arsenic, so far from throwing any obstacle in the way of the metallic reproduction of that substance, are the very steps which should be adopted as preparatory to the “experimentum crucis.” It is only necessary to collect the precipitates, and to decompose them in the manner already described; and this confirmation of our results should never be neglected, for it is the bounden duty of the forensic chemist, who is called upon to decide so important a question as the presence of a corrosive poison, to prosecute by the fullest enquiry every point which admits of the least doubt; he should also remember that in a criminal case, where the life of a human being depends upon his testimony, he has not only to satisfy his own conscience, but that he is bound, as far as he is able, to convince the public mind of the accuracy and truth of his researches.
2. The Arsenious Acid is mixed with various alimentary and other substances.
The detection of the presence of arsenic, amidst a complicated mass of alimentary matter, has long been a problem of interest and difficulty. In the directions which have been already offered for the discovery of arsenic in solution, we have in some measure anticipated several of the resources, of which we are now to avail ourselves. It has been seen how greatly coloured fluids are capable of obscuring, and changing, and even altogether preventing, the arsenical indications. M. Orfila, with an assiduity and accuracy which so eminently characterise all his toxicological labours, has accordingly investigated the peculiar appearances assumed by the arsenical precipitates in different media, such as bile, tea, coffee, wine, broth, jelly, &c. Since the publication of the great work[[260]] in which these phenomena are recorded, its author has proposed a new method[[261]] of removing its difficulties and embarrassments, occasioned by the colouring matter of the above media; which consists in a previous application of Chlorine, so as to change the colour to a shade, that will not offer any optical impediment to the characteristic indications of the tests in question. We are ready to admit that such a mode of proceeding may, on certain occasions, assist the accomplished chemist in his analysis; but in the hands of a person less accustomed to chemical manipulation, we hesitate not to declare that it is subject to fatal fallacies; whereas, by collecting the precipitate, and submitting it to the process of sublimation we shall at once obtain the arsenious acid in a pure form, and be enabled to test it, in distilled water without the chance of error. Why then should we attempt to pursue our game through the windings of a labyrinth, when a direct road lies before us by which we may drive it into the open plain?
We accordingly recommend the juridical chemist, who suspects the presence of arsenious acid in broth, coffee, or any coloured liquid, to add a solution of ammoniuret of silver, and thus to precipitate indiscriminately all the bodies which it may be capable of so affecting. The precipitate may then be collected, and submitted to heat in a glass tube, as before directed.
But the Arsenious acid may perchance be so mixed with various foreign matter as to render its separation by filtration difficult; in such a case, after having boiled it in distilled water, in order to procure all the soluble matter from it, the residual mass may be evaporated to dryness, care being taken that the heat applied for such a purpose never exceeds 250° Fah. or we shall lose the arsenic, should any be present, by volatilization. The residue thus obtained may then be submitted to a higher temperature in a subliming vessel, in order to procure the arsenious acid in its pure state. This process applies particularly to the examination of the matter vomited, or the feculent evacuations passed, by the patient. Should the arsenious acid have, in the first instance, been dissolved in oil, Dr. Ure proposes to boil the solution in distilled water, and to separate the oil afterwards by the capillary action of wick threads. If the arsenious acid be mixed with resinous bodies, Oil of Turpentine may be employed as their solvent, which will leave the arsenic untouched. Dr. Black directed the application of alcohol for this purpose, but this is obviously improper, since arsenious acid is soluble in that fluid.
If the physician be called upon to investigate the contents of the alimentary canal after death, and the arsenious acid cannot be discovered amongst the suspected matter, the stomach itself must be cut into small pieces, and in compliance with the directions of Orfila, boiled in ten or twelve times their weight of distilled water, which should be renewed as fast as a portion of it flies off in vapour; this liquor should be cooled and decanted, in order to put a few drops of it into the solutions of the different re-agents which we have before described. If the precipitates should indicate the presence of arsenic, we may proceed according to the directions we have already laid down; if, on the other hand, the fluid offers no indication of poison, the mass exhausted by water should be treated, according to the process suggested by Rose, by boiling it for some time in a solution of potass, by which means the stomach will be partly decomposed and dissolved, and the arsenious acid, with which it might have been combined, saturated by the alkali. In this state the liquor is to be filtered, again boiled, and nitric acid added, little by little, until it passes from a dark to a clear yellow colour. The object of the acid in this stage of the process being to decompose and destroy the animal matter. The excess of acid should be saturated with potass, when an Arsenite of Potass will be formed, if there really existed any arsenious acid in the stomach. This M. Orfila recommends us to precipitate by the Hydro-sulphuret of Ammonia, and a few drops of nitric acid; (Rose prefers lime water for the same purpose); a yellow sulphuret of Arsenic will be the result, from which the whole of the metal may be obtained, by drying it upon a filter, mixing it with an equal bulk of potass, and melting it in a small glass tube.
This complicated mode of proceeding will rarely be found necessary; but it should not be neglected, where the presence of arsenic cannot be otherwise detected in the alimentary canal of those who are suspected to have died from its ingestion, especially in the examination of a body where, from the length of time it may have been under ground, there is reason to suppose that the acid exists in a state of intimate combination with the animal matter. And we may take this opportunity to observe, that advanced putrefaction, however disagreeable it may render such researches, will not, in the case of arsenic, defeat their success; let the forensic physician, then, remember, that the length of time which may have elapsed since the death of the body, ought never to be urged as a plea for not having proceeded in its dissection. The task may be personally disagreeable, but it will be less painful than the reflections which must attend a breach of duty; upon such an occasion we would address the anatomist in the quaint but expressive words of Teichmeyer[[262]], “Præstat enim manus quam conscientiam cruentare et contaminare.”