VIII 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 processes.
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.