PICRIC ACID (from Gk. /twos, pikros, bit ter), or CAu.vz(rrtc Auto, One of the first organic dyes that have been prepared by artificial processes. It is derived from car• bone acid, or phenol, by the action of nitric acid. and is therefore called also trinitrocarbolie acid or trinitrophenol. It is best prepared by dissolving carbolic acid in strong sulphuric acid and gradually adding nitric acid; after the vio lent action has subsided. the mixture is kept for about two hours at a gentle heat, so as to C0111 plete the reaction. Picric acid separates out ill crystalline form front the solution thus obtained, and may be purified by crystallization from hot water, in which it is moderately soluble. The acid is also formed by the action of nitric acid on many organic products, such as wool, leather, silk, indigo, resins. etc. While it is but sparingly soluble in void water, it readily dissolves in organic liquids like ordinary ether, benzene, etc. Its solutions have a strongly bitter taste and stain the skin as well as wool and silk a bright yellow. Formerly picric acid was much used as Id (1VV. Since vegetable fibres are not colored by it, it may be used to detect cotton mixed in with wool. At present picric acid is used extensively for the manufaeture of certain ex plosives. The acid itself burns quietly if ignited; but its alkali derivatives, the pirsatcs of sodium, potassium. and ammonium, explode when heated,
with great violence. It is mostly these deriva tives of picric acid that are employed in the manufacture of explosives. The explosive known as atelinite, however, consists mainly of the free acid. Formerly the acid was largely used in the manufacture of smokeless powder. l'icric acid is said to have been employed also as a substitute for hops in the manufacture of beer. In France the acid is commonly used as a remedy for burns, as it is believed to prevent the formation of blisters. A small quantity of the acid is dis solved in a little alcohol, and the solution is di luted with a large amount of cold water; the solution is constantly applied to the burned part until the smarting pain has ceased.
organic ehemistry picric acid is classed with the phenols, being a benzene derivative containing the hydroxyl group (OH). Unlike most other phenols. however, it is more strongly acid than carbonic acid, from the combinations of which (the carbonates) it is capable of taking away the alkali metals, to form 'Aerates. These strong ly acid properties of picric acid (trinitropfienol) are due to the presence of nitro-groups in its molecule.