When powdered bark is treated with tincture of iodine, little effect is visible in the case of pure cinnamon of good quality, but when cassia is present a deep-blue tint is produced, the intensity of the coloration depending on the proportion of the cassia.
Chalcopyrite is decomposed by nitric acid with separation of sulphur and formation of a green solution; ammonia added in excess to this solution changes the green colour to deep blue and precipitates red ferric hydroxide.
With ferric salts its solution gives a deep blue colour, and with ferrous salts, after exposure to the air, an insoluble, blue-black, ferroso-ferric gallate.
In 1906 Lunge (in a paper published with Bert) to some extent modified his views, by introducing an intermediate compound, sulphonitronic acid, SO 5 NH 2, which had been noticed by various chemists for some time through its property of imparting a deep blue colour to sulphuric acid.
It is a fuming liquid, which is soluble in benzene and in acetic acid; it dissolves in water to form a deep blue solution.