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Articles from Aids To Forensic Medicine And Toxicology

Mental Unsoundness

Copper And Its Preparations

Incised Wounds And Those Accompanied By Solution Of Continuity

Lead And Its Preparations

Personal Identity

Mercury And Its Preparations

Chloral Hydrate

Idiocy Imbecility Cretinism

Wounds And Mechanical Injuries


Detection Of Poisons

Notice the smell, colour, and general appearance, of the matter
submitted for examination. The odour may show the presence of prussic
acid, alcohol, opium, or phosphorus. The colour may indicate salts of
copper, cantharides, etc. Seeds of plants may be found.

This examination having been made, the contents of the alimentary canal,
and any other substances to be examined, must be submitted to chemical

Simple filtration will sometimes suffice to separate the required
substance; in other cases dialysis will be necessary, in order that
crystalloid substances may be separated from colloid bodies.

In the case of volatile substances distillation will be required. The
poisons thus sought for are alcohol, phosphorus, iodine, chloral,
ether, hydrocyanic acid, carbolic acid, nitro-benzol, chloroform, and
anilin. The organic matters are placed in a flask, diluted with
distilled water if necessary, and acidulated with tartaric acid. The
flask is heated in a water-bath, and the vapours condensed by a Liebig's
condenser. In the case of phosphorus the condenser should be of glass,
and the process of distillation conducted in the dark, so that the
luminosity of the phosphorus may be noted.

For the separation of an alkaloid, the following is the process of
Stas-Otto. This process is based upon the principle that the salts of
the alkaloids are soluble in alcohol and water, and insoluble in
ether. The pure alkaloids, with the exception of morphine in its
crystalline form, are soluble in ether. Make a solution of the
contents of the stomach or solid organs minced very fine by digesting
them with acidulated alcohol or water and filtering. The filtrate is
shaken with ether to remove fat, etc., the ether separated, the watery
solution neutralized with soda, and then shaken with ether, which
removes the alkaloid in a more or less impure condition. The knowledge
of these facts will help to explain the following details, which may be
modified to suit individual cases: (1) Treat the organic matter, after
distillation for the volatile substances just mentioned, with twice its
weight of absolute alcohol, free from fusel oil, to which from 10 to 30
grains of tartaric or oxalic acid have been added, and subject to a
gentle heat. (2) Cool the mixture and filter; wash the residue with
strong alcohol, and mix the filtrates. The residue may be set aside for
the detection of the metallic poisons, if suspected. Expel the alcohol
by careful evaporation. On the evaporation of the alcohol the resinous
and fatty matters separate. Filter through a filter moistened with
water. Evaporate the filtrate to a syrup, and extract with successive
portions of absolute alcohol. Filter through a filter moistened with
alcohol. Evaporate filtrate to dryness, and dissolve residue in water,
the solution being made distinctly acid. Now shake watery solution with
ether. (3) Ether from the acid solution dissolves out colchicin,
digitalin, cantharidin, and picrotoxin, and traces of veratrine
and atropine. Separate the ethereal solution and evaporate. Hot water
will now dissolve out picrotoxin, colchicin, and digitalin, but
not cantharidin. (4) The remaining acid watery liquid, holding the other
alkaloids in solution or suspension, is made strongly alkaline with
soda, mixed with four or five times its bulk of ether, chloroform, or
benzole, briskly shaken, and left to rest. The ether floats on the
surface, holding the alkaloids, except morphine, in solution. (5) A part
of this ethereal solution is poured into a watch-glass and allowed to
evaporate. If the alkaloid is volatile, oily streaks appear on the
glass; if not volatile, crystalline traces will be visible. If a
volatile alkaloid, add a few pieces of calcium chloride to ethereal
solution to absorb the water; draw off the ethereal solution with a
pipette, allow it to evaporate, and test the residue for the alkaloids,
conine and nicotine.

If a fixed alkaloid, treat the acid solution with soda or potash and
ether, evaporate ethereal solution after separation, when the solid
alkaloid will be left in an impure state. To purify it, add a small
quantity of dilute sulphuric acid, and, after evaporating to
three-quarters of its bulk, add a saturated solution of carbonate of
potash or soda. Absolute alcohol will then dissolve out the alkaloid,
and leave it on evaporation in a crystalline form.

General Reactions for Alkaloids.--(1) Wagner's reagent (iodine
dissolved in a solution of potassium iodide) yields a reddish-brown
precipitate; (2) Mayer's reagent (potassio-mercuric iodide) gives a
yellowish-white precipitate; (3) phospho-molybdic acid gives a yellow
precipitate; (4) platinic chloride, a brown precipitate; (5) tannic
acid, etc.

In order to isolate an inorganic substance from organic matter,
Fresenius's method is adopted. Boil the finely divided substance with
about one-eighth its bulk of pure hydrochloric acid; add from time to
time potassic chlorate until the solids are reduced to a straw-yellow
fluid. Treat this with excess of bisulphate of sodium, then saturate
with sulphuretted hydrogen until metals are thrown down as sulphides.
These may be collected and tested. From the acid solution, hydrogen
sulphide precipitates copper, lead, and mercury, dark; arsenic,
antimony, and tin, yellowish. If no precipitate, add ammonia and
ammonium sulphide, iron, black, zinc, white, chromium, green,
manganese, pink. The residue of the material after digestion with
hydrochloric acid and potassium chlorate may have to be examined for
silver, lead, and barium.

For the detection of minute quantities, the microscope must be used, and
Guy's and Helwig's method of sublimation will be found advantageous.
Crystalline poisons may be recognized by their characteristic forms.

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