There is often some clue as to the nature of the poison afforded, and the investigation should be made for it first; the presence or absence of other poisons, however, must be determined. If there be no clue, then a systematic examination must be carried out. The poison must be looked for not only in the contents of the stomach, but in the viscera as well; it must be remembered that poison may be introduced into the stomach after death. Volatile poisons, such as alcohol, chloroform, prussic acid, may be separated by distillation after acidulation with tartaric acid. Arsenic is best separated by drying the organic material, and distilling after adding strong hydrochloric acid. Other metallic poisons may be tested for, with or without destruction of organic matter. To destroy the organic matter, the _moist method_ is the one in general use: After reducing the contents of the stomach or the viscus to a pulp, they are mixed with distilled water to the consistency of thin gruel, and placed in a flask with some crystals of potassium chlorate--half an ounce to each pound of the liquid. Pure hydrochloric acid is added, and the flask gently heated on a water bath, a mixture of chlorine and oxides of chlorine is given off and gradually breaks up the organic matter, converting at the same time any mineral poison present into the chloride. This procedure is followed until the material becomes quite limpid, more chlorate or hydrochloric acid may be added if necessary. It is then transferred to an evaporating dish and heated on the water bath until the smell of chlorine disappears. It is then filtered while hot, to allow chloride if present to pass through; a stream of sulphur dioxide is passed through the filtrate when cold, to reduce any metals present to a lower state of oxidation. Silver chloride will not pass through the filter in this process, so it has to be dealt with in a special manner. In making a systematic analysis, volatile poisons must be tested for first, then ascertain the presence or absence of alkaloids, after which the inorganic poisons must be dealt with. CHAPTER II DIVISION I.--CHEMICAL CORROSIVE POISONS THE MINERAL ACIDS _General Characters._--The mineral acids have no remote effects on the system; their action is purely local. They are seldom used for the purpose of homicide, except in the case of young children. By suicides they are more frequently employed.