Hydrolysis by alkaline solutions gives a sugar and caffeic acid; whilst fusion with potassium hydroxide gives protocatechuic acid.
Its action upon turmeric is characteristic; a turmeric paper moistened with a solution of boric acid turns brown, the colour becoming much darker as the paper dries; while the addition of sodium or potassium hydroxide turns it almost black.
The solution obtained may be evaporated in vacuo until it attains a density of 1.46 when, if partially saturated with potassium hydroxide and filtered, it yields crystals of potassium pentathionate, K 2 S 5 0 6.3H 2 0.
With potassium hydroxide it yields potassium silicofluoride,.
Chromous oxide, CrO, is unknown in the free state, but in the hydrated condition as Cr04H 2 0 or Cr(OH) 2 it may be prepared by precipitating chromous chloride by a solution of potassium hydroxide in air-free water.
Cadmium hydroxide, Cd(OH) 2, is obtained as a white precipitate by adding potassium hydroxide to a solution of any soluble cadmium salt.
On standing with concentrated potassium hydroxide solution it gives potassium allantoate C 4 H 7 N 4 O 4 K.
Sodium and potassium hydroxide solutions precipitate green chromium hydroxide from solutions of chromic salts; the precipitate is soluble in excess of the cold alkali, but is completely thrown down on boiling the solution.
Zinc and hydrochloric acid in the cold convert it into alloxantin, hydroxylamine gives nitroso-barbituric acid, C 4 H 2 N 2 0 3: NOH, baryta water gives alloxanic acid, C 4 H 4 N 2 0 5, hot dilute nitric acid oxidizes it to parabanic acid, hot potassium hydroxide solution hydrolyses it to urea and mesoxalic acid and zinc and hot hydrochloric acid convert it into dialuric acid, C4H4N204.
In Fleitmann's test, the solution containing the arsenious compound is mixed with pure potassium hydroxide solution and a piece of pure zinc or aluminium foil dropped in and the whole then heated.