_Post-Mortem Appearances._--Where the acid has come in contact with the mucous membranes there are dark brown or black patches. The stomach is greatly contracted, the summits of the mucous membrane ridges being charred and the furrows greatly inflamed; the contents are black or brown. _Tests._--Concentrated acid chars organic matter; evolves heat when added to water, and sulphurous fumes when boiled with chips of wood, copper cuttings, or mercury. Dilute acid chars paper when the paper is heated; gives a white precipitate with nitrate or chloride of barium, and is entirely volatilized by heat. Dilute solutions give a white precipitate with barium nitrate, insoluble in hydrochloric acid even on boiling. _Fatal Dose._--In an adult, 1 drachm. _Fatal Period._--Shortest, three-quarters of an hour; average period from onset of primary effects, eighteen to twenty-four hours. XI.--NITRIC ACID =Nitric Acid=, or aqua fortis, is less frequently used as a poison than sulphuric acid. The fumes from nitric acid have caused death from pneumonia in ten or twelve hours. _Method of Extraction from the Stomach._--The same as for sulphuric acid. In beer, etc., the mixture may be neutralized with carbonate of potassium, dialyzed, the fluid concentrated and allowed to crystallize, when crystals of nitrate of potassium may be recognized. _Post-Mortem Appearance._--The mucous membranes are rendered yellow or greenish if bile be present; they are also thickened and hardened. _Tests._--Concentrated acid gives off irritating orange-coloured fumes of nitric acid gas. When poured on copper, it gives off red fumes and leaves a green solution of nitrate of copper. It gives a red colour with brucine, turns the green sulphate of iron black, and with hydrochloric acid dissolves gold. A delicate test for the acid, free or in combination, is to dissolve in the suspected fluid some crystals of ferrous sulphate, and then to gently pour down the test-tube some strong sulphuric acid. Where the two liquids meet, if nitric acid be present, a reddish-brown ring will be formed. It turns the skin bright yellow, and does the same with woollen clothes, from the formation of _picric_ acid. _Fatal Dose._--Two drachms. _Fatal Period._--Shortest, one hour and three-quarters in an adult; in infants in a few minutes, from suffocation. XII.--HYDROCHLORIC ACID =Hydrochloric Acid=, muriatic acid, or spirit of salt, is not uncommonly used for suicidal purposes, being fifth in the list. _Method of Extraction from the Stomach._--The same as for sulphuric acid. As hydrochloric acid is a constituent of the gastric juice, the signs of the acid must be looked for. _Post-Mortem Appearances._--The mucous membranes are dry, white, and shrivelled, and often eroded.