Where the pure earth, baryta, or its solution in water, is presented for our investigation, it may be identified by the following reagents.
(a) Sulphuric acid, and the soluble sulphates. These bodies precipitate from the barytic solution, a white sulphate of the earth, insoluble in water, and nitric acid.
(b) Carbonic acid gas, and the alkaline sub-carbonates, produce in it a white carbonate of baryta.
(c) Muriatic acid combines with baryta, and furnishes a salt which is capable of being identified by numerous reagents. M. Orfila has furnished us with the following satisfactory compendium of its habitudes. “A salt which does not redden the tincture of tournesol, which does not turn the syrup of violets green, which is not precipitated by the alkaline hydro-sulphurets,[[336]] nor by ammonia; but which, on the contrary, is precipitated by the sub-carbonate of ammonia, soda, or potass; which is not soluble in concentrated alcohol; which furnishes, with the sulphate of potass, or the sulphuric acid, a white precipitate insoluble in water and in the nitric acid, and which gives with the nitrate of silver a curdled precipitate of muriate of silver, likewise insoluble in the nitric acid, can be no other than the muriate of baryta.”
But it may happen, that the above salt is so mixed with alimentary matter, as to defy the action of the tests; in this case we must endeavour to obtain from it the pure earth, by precipitating the suspected fluids by the sub-carbonate of ammonia; when a carbonate of baryta will fall down, which must be dried on a filter, and calcined with charcoal.
Cantharides. Spanish Flies—Blistering Flies. (Cantharis Vesicatoria, Sp. 1, of Latreille.)[[337]]
Cantharides are imported into this country in their entire state, and are so kept in the shops; their form and general appearance are too well known to require description, and they will rarely become the objects of inquiry; in powder, however, they may be presented to us for investigation, and it is therefore essential that the forensic physician should be acquainted with the appearances which they assume in the state of disintegration. This powder has a greenish colour, tinged with grey, and abounding with shining points of a very beautiful green colour, and which may be recognised in whatever state of division the powder may exist, even after it has passed through a silken sieve. Its odour is acrid and nauseous; when thrown on burning coals it emits that peculiar smell, which generally attends the destruction of animal matter by heat. The chemical history of cantharides is still involved in some obscurity; according to Robiquet, who has furnished us with the most satisfactory analysis, they contain various fatty principles; the phosphates of lime, and magnesia; and the acetic and uric acids; together with a peculiar crystalline principle, in which the vesicatory properties wholly reside, and to which the name of cantharidin has been given by Dr. Thomson.[[338]] It may be obtained in plates, having a micaceous lustre; when perfectly pure it is insoluble in water, but it is rendered soluble in that fluid, by the presence of a yellow matter which exists in native combination with it; it is very soluble in oils.
Symptoms of poisoning by Cantharides.
As this substance forms an article of the materia medica it may become an accidental source of poisoning; whilst a general belief in its aphrodisiac powers may induce a trial of its efficacy, to goad the exertions of exhausted nature, or to incense the passion of females, whose seduction is meditated. In the annals of crime in this country, we are acquainted with but few instances in which cantharides have been given with the view of destroying life; we have already referred[[339]] to the case of Vaux, who was executed for poisoning with cantharides; there is also that of Sir Thomas Overbury, who, on the confession of the person who gave it to him, is said to have taken it, mixed with his sauces. Cantharides may be administered in the form of powder, infusion, or tincture. The following may be considered the more prominent symptoms which will follow the ingestion of a large dose. Violent retching; copious alvine evacuations, frequently bloody; very severe colics; active inflammation of the stomach and intestines; sometimes universal convulsions, attended with a horror of liquids, resembling that which occurs in hydrophobia; furious delirium, &c. But the affections of the urinary passages, and organs of generation, may be regarded, κατεξοχην, as the peculiar symptoms of poisoning by cantharides; such as heat in the bladder, bloody micturition; horrible strangury; painful and obstinate priapism; satyriasis, &c. If the dose has not been sufficient to occasion speedy death, it may produce marasmus.