Phosphorous acid is an inorganic compound, Soluble in water and alcohol. Decomposed into phosphoric acid and phosphine (toxic, explosive) is slowly oxidized in air, phosphoric acid, heated to 180 ℃. Phosphorous acid is a dibasic acid, which is slightly stronger acid than phosphoric acid, which has a strong reduction of silver ions easily (Ag +) is reduced to metallic silver (Ag), sulfur dioxide can be reduced to sulfuric acid. Strong hygroscopicity and deliquescence, corrosive.