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.
These are sulphuric, nitric, and hydrochloric acids.
_Symptoms of Poisoning by the Mineral Acids._--Acid taste in the mouth, with violent burning pain extending into the oesophagus and stomach, and commencing immediately on the poison being swallowed; eructations, constant retching, and vomiting of brown, black, or yellow matter containing blood, coagulated mucus, epithelium, or portions of the lining membrane of the gullet and stomach. The vomited matters are strongly acid in reaction, and stain articles of clothing on which they may fall. There is intense thirst and constipation, with scanty or suppressed urine, tenesmus, and small and frequent pulse; the lips, tongue, and inside of the mouth, are shrivelled and corroded. Exhaustion succeeds, and the patient dies either collapsed, convulsed, or suffocated, the intellect remaining clear to the last. After recovering from the acute form of poisoning, the patient may ultimately die from starvation, due to stricture of the oesophagus, stomach, etc.