_Tests._--The concentrated acid yields dense white fumes with ammonia. When warmed with black oxide of manganese and strong sulphuric acid it gives off chlorine, recognized by its smell and bleaching properties. Diluted it gives with nitrate of silver, a white precipitate, which is insoluble in nitric acid and in caustic potash, but is soluble in ammonia, and when dried and heated melts, and forms a horny mass. Stains on clothing are reddish-brown in colour. _Fatal Dose._--Half an ounce. _Fatal Period._--Shortest, two hours; average, twenty-four hours. Death may occur after an interval of some weeks from destruction of the gastric glands and inability to digest food. XIII.--OXALIC ACID =Oxalic Acid= is used by suicides, though not often by murderers. The crystals closely resemble those of Epsom salts or sulphate of zinc; oxalic acid has been taken in mistake for the former. It is in common use for cleansing brass, in laundry work, for dyeing purposes, and especially for bleaching straw hats. _Symptoms._--If a concentrated solution be taken, it acts as a corrosive, causing a burning acid, intensely sour taste, which comes on immediately, great pain and tenderness and burning at pit of stomach, pain and tightness in throat. Vomiting of mucus, bloody or dark coffee-ground matters, purging and tenesmus, followed by collapse, feeble pulse, cyanosis and pallor of the skin; also swelling of tongue, with dysphagia. In some cases cramps and numbness in limbs, pain in head and back, delirium and convulsions. May be tetanus or coma. If taken freely diluted, the nervous symptoms predominate, and may resemble narcotic poisoning. Sometimes almost instant death. _Post-Mortem Appearances._--Mucous membrane of mouth, throat, and gullet, white and softened, as if they had been boiled; there are often black or brown streaks in it. Stomach contains dark, grumous matter, and is soft, pale, and brittle. Intestines slightly inflamed, stomach sometimes quite healthy. _Treatment._--Warm water, then chalk, carbonate of magnesium, or lime-water, freely. Not alkalies, as the oxalates of the alkalies are soluble and poisonous. Castor-oil. Emetics, but not stomach-pump. _Fatal Dose._--One drachm is the smallest, but half an ounce is usually fatal. _Method of Extraction from the Stomach._--Mince up the coats of the stomach and boil them in water, or boil the contents of the stomach and subject them to dialysis. Concentrate the distilled water outside the tube containing the vomited matters, etc., and apply tests. _Tests._--White precipitate with nitrate of silver, soluble in nitric acid and ammonia. When the precipitate is dried and heated on platinum-foil, it disperses as white vapour with slight detonation. Sulphate of lime in excess gives a white precipitate, soluble in nitric or hydrochloric acid, but insoluble in oxalic, tartaric, acetic, or any vegetable acid.