Prop., Uses &c. The chromates are characterised by their yellow or red colour, the latter predominating when the acid is in excess; and except those with the alkaline bases, they are, for the most part, insoluble in water. Both the chromate and the bichromate of potassium are extensively used in dyeing and calico-printing. The former is employed in conjunction with sulphuric acid in the laboratory as an oxidising agent and in the manufactory for bleaching sperm oil. The bichromate of ammonium and potassium are used in photography.
They are readily recognised by the following tests:—
On boiling a chromate in hydrochloric acid mixed with alcohol, chromic acid is first set free, and then decomposed, forming a green solution of chloride of chromium. Sulphuretted hydrogen and sulphurous acid effect similar changes. With acetate of lead the chromates give a yellow precipitate; with nitrate of silver, a reddish-brown; with nitrate of mercury, a red one.
CHROME ALUM. See Alums.
CHROME GREEN. See Green Pigments.
CHROME IRON. See Iron.
CHROME RED. See Red Pigments.
CHROME YELLOW. See Lead, Chromate of.
CHROMIC ACID. See Chromic Anhydride.
CHRO′MIUM. Cr. A metal discovered in native chromate of lead by Vauquelin in 1797. It is found in the state of oxide, combined with oxide of iron, in some abundance, in the Shetland Islands, and elsewhere; as chromate of lead it constitutes a very beautiful material.