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.

Detection Of Blood-stains Etc Digitalis facebooktwittergoogle_plusredditpinterestlinkedinmail