NITRIC ACID
Forms.—Strong nitric acid, and dilute nitric acid.
Characters.—This acid is commonly known as aqua fortis, or red spirit of nitre. It is seldom used as a poison.
The strong acid varies in colour from a pale yellow to a deep orange. The colour is due to admixture with peroxide of nitrogen. On cloth and articles of dress it produces yellow stains, which are darkened by the application of an alkali. If poured on copper cuttings, reddish fumes of nitrous acid are given off. Dilute nitric acid is a colourless acid liquid, not precipitated by nitrate of barium or nitrate of silver, showing absence of sulphuric and hydrochloric acids. All its alkaline salts are soluble in water.
Symptoms.—The symptoms have been before described, and are similar to those produced by sulphuric acid, though not quite so severe. The vapour of this acid has caused death in eleven hours by congestion of the bronchial tubes and lungs; care should, therefore, always be taken not to inhale the fumes given off by the acid in the manufacture of gun-cotton, &c.
Post-mortem Appearances.—Same as the mineral acids generally, but the tissues touched are turned yellow, and if bile be in the stomach it is turned green. The stomach is rarely perforated.
Chemical Analysis.—Nitric, like sulphuric, acid will be examined under four heads; but being a volatile acid, easily decomposed, and also having its nature changed by contact with organic substances, its presence on clothes may fail to be detected after a few weeks. The colour of the stain on cloth may also remain, although the acid has been entirely removed by washing. 1. Strong, concentrated acid. 2. Dilute acid. 3. Mixed with organic liquids, &c. 4. On the clothes of the person injured.
I. Concentrated Acid
1. Volatility.—When exposed to the atmosphere, strong nitric acid gives off colourless or orange-coloured acid fumes. Heated in a watch-glass, it is evaporated without residue.
2. Action on Organic Matter.—The acid leaves on woollen clothes a yellow-coloured stain, which is darkened by the addition of an alkali. The colour of the stain is due to the formation of picric acid.