But at the same time it is equally obvious, that in medico-legal analyses, unless the reagents used be previously known to be free of arsenic, they ought invariably to be subjected in the first instance to the process, whatever it may be, which the analyst proposes to employ for detecting arsenic in a suspected substance.
2. Arsenic may be present in some articles of chemical apparatus.—Arsenic has been detected in the metal of cast-iron pots,[[542]] which Orfila and others have proposed to employ in certain analyses on the large scale, as, for example, when the poison is sought for in the whole soft solids of the human body. It is denied, however, that any of that arsenic can be dissolved out of cast-iron by the process which has been followed in such circumstances.[[543]]
The primary fact, and the qualification of it, are in my opinion of equally little medico-legal importance. It is not likely that such enormous masses of material will ever be operated on again, as those which were made use of in some late, French trials, and for which great iron pots were found indispensable;—because it has been proved that absorbed arsenic is chiefly to be met with in particular organs or secretions, such as the liver and urine. Besides, a false importance has been attached to the enthusiastic analyses of the whole human carcase, with which some French chemists have been astounding the minds of the scientific world, as well as the vulgar, on the occasion of certain late trials for poisoning. I confess I could not find fault with a jury, who might decline to put faith in the evidence of poisoning with arsenic, when the analyst, after boiling an entire body, with many gallons of water, in a huge iron cauldron, making use of whole pounds of sulphuric acid, nitric acid, and nitre, and toiling for days and weeks at the process, could do no more than produce minute traces of the poison. What man of common sense will believe, that, with such bulky materials and crude apparatus, it is possible to guard to a certainty against the accidental admission of a little arsenic? At all events I am much mistaken if any British jury would condemn a prisoner on such evidence,—or any British chemist find fault with them for declining to do so.
3. Arsenic may have existed in antidotes administered during life.—It is now generally known, that the only chemical antidote for arsenic is the hydrated sesquioxide of iron. But this substance appears occasionally to contain a little arsenic, obviously derived from the compound of iron whence the oxide is prepared.[[544]] Such an adulteration must be rare in what is prepared by the ordinary processes, according to which the oxide of arsenic ought to remain in solution. The only effectual mode, however, of guarding against this source of error, when the antidote has been administered, is to examine a portion of the stock whence the patient was supplied, by dissolving it in an excess of sulphuric acid, and subjecting it to Marsh’s test.
4. Arsenic sometimes exists naturally in the human body.—This startling proposition was first advanced by M. Couerbe, and by Professor Orfila soon afterwards.[[545]] The latter subsequently stated, that it exists only in the bones, and not in any of the soft solids.[[546]] It is now clear, however, that both of these experimentalists must have committed an error. Orfila himself admits that his early researches are vitiated by the subsequent discovery of arsenic in some kinds of sulphuric acid;[[547]] and all recent attempts by others to obtain his results have failed. Thus MM. Flandin and Danger could not detect arsenic in any part of the human body, when it had not been administered:[[548]] Pfaff was unable to detect an atom of it in the bones of man or the lower animals by Orfila’s own process:[[549]] Dr. Rees was equally unsuccessful:[[550]] and in 1841 a committee of the French Institute, who superintended the performance of an analysis in three cases by Orfila, reported that he failed in every instance to find a trace of arsenic, by a process which could detect a 65th part of a grain intentionally mixed with an avoirdupois pound of bones.[[551]]
There is the strongest possible presumption, therefore, that human bones never contain any arsenic. And besides, supposing they did, the source of fallacy would be utterly insignificant; for, when it becomes necessary to search for arsenic absorbed into the textures of the body, it is never necessary to have recourse to the bones.
5. Arsenic may exist in the soil of churchyards.—This proposition too was first announced by Professor Orfila, who found a little in the churchyard of Villey-sur-Tille, near Dijon, and of the Bicêtre, Mont-Parnasse, and New Botanic Garden at Paris.[[552]] And although MM. Flandin and Danger afterwards denied they could ever find any,[[553]] a committee of the Parisian Academy of Medicine reported that Orfila proved before them the accuracy of his statement.[[554]] But the arsenic exists in a state in which it cannot be dissolved out by boiling water: It has been hitherto separable only by boiling the churchyard mould with concentrated sulphuric acid. Hence it cannot pass by percolation through a coffin into a body; and consequently it becomes a source of fallacy only when the coffin has been broken up in the course of time, and the mould lies in actual contact with the organs to be analysed.[[555]]
It plainly appears, then, that most of the fallacies alleged against the validity of the evidence derived from the discovery of arsenic within the human body in cases of poisoning have no real existence; and that those which are real can easily be provided against by simple and obvious precautions.
3. Arsenite of Copper.
The arsenite of copper [Scheele’s-green, Mineral-green] deserves notice, because it is in use as a pigment, and has actually been used as a poison. Dr. Duncan once detected it in pills, given to a pregnant female with the view of procuring abortion; in Paris it has been detected in sweetmeats, having been used to give them a fine green colour;[[556]] and Mr. Ainley of Bingley in Yorkshire informs me he found it to constitute a pigment sold by London pastry-cooks under the name of emerald-green for colouring preserves, and which in his practice had proved poisonous to children who had eaten apple-tarts coloured with it.