Chromates

Chromates. These substances are the salts of the acid known as chromic acid, H₂Cr0₄. or compounds of metallic oxides with chromic oxide, Cr0₃. The normal chromates are analogous to the acid above as, K₂Cr0₄, the salts known as bichromates or dichromates contain a double proportion of the chromic oxide, as K₂Cr₂0₂. They are an important series of bodies, many of considerable practical importance; they are all coloured, varying in hue from yellow to dark red. Potassium bichromate (red, triclinic system) is largely manufactured from chrome iron ore, and is used for preparation of the other chromates, in dyeing, in photographic printing (carbon process), and for a variety of other purposes. Lead chromate, PbCrO₄, occurs native as crocoisite, and is artificially prepared for use as the pigment chrome yellow, a basic chromate Pb₂Cr0₅ is known as chrome red, and a mixture of these two forms chrome orange. Other chromates are largely employed for scientific purposes in the chemical laboratory.