Picric acid crystallises in yellow shining prisms or laminae having an intensely bitter taste, and is poisonous. It melts at 122.5 deg. C., sublimes when cautiously heated, dissolves sparingly in cold water, more easily in hot water, still more in alcohol. It stains the skin an intense yellow colour, and is used as a dye for wool and silk. It is a strong acid, forming well crystallised yellow salts, which detonate violently when heated, some of them also by percussion. The potassium salt, C_{6}H_{2}(NO_{2})_{3}OK, crystallises in long needles very slightly soluble in water. The sodium, ammonium, and barium salts are, however, easily soluble in water. Picric acid, when heated, burns with a luminous and smoky flame, and may be burnt away in large quantity without explosion; but the mere contact of certain metallic oxides, with picric acid, in the presence of heat, develops powerful explosives, which are capable of acting as detonators to an indefinite amount of the acid, wet or dry, which is within reach of their detonative influence. The formula of picric acid is C_{6}H_{2}|(NO_{2})_{3} |OH. which shows its formation from phenol (C_{6}H_{5}OH.), three hydrogen atoms being displaced by the NO_{2} group. The equation of its formation from phenol is as follows:-- C_{6}H_{5}.OH + 3HNO_{3} = C_{6}H_{2}(NO_{2})_{3}OH + 3H_{2}O. According to Berthelot, its heat of formation from its elements equals 49.1 calories, and its heat of total combustion by free oxygen is equal to +618.4 cals. It hardly contains more than half the oxygen necessary for its complete combustion. 2C_{6}H_{2}(NO_{2})_{3}OH + O_{10} = 12CO_{2} + 3H_{2} + 3N_{2}. The percentage composition of picric acid is--Nitrogen, 18.34; oxygen, 49.22; hydrogen, 1.00; and carbon, 31.44, equal to 60.26 per cent. of NO_{2}. The products of decomposition are carbonic acid, carbonic oxide, carbon, hydrogen, and nitrogen, and the heat liberated, according to Berthelot, would be 130.6 cals., or 570 cals. per kilogramme. The reduced volume of the gases would be 190 litres per equivalent, or 829 litres per kilogramme. To obtain a total combustion of picric acid it is necessary to mix with it an oxidising agent, such as a nitrate, chlorate, &c. It has been proposed to mix picric acid (10 parts) with sodium nitrate (10 parts) and potassium bichromate (8.3 parts). These proportions would furnish a third of oxygen in excess of the necessary proportion.