In aqueous solution, yellow chromate (CrO42-) and orange dichromate (Cr2O72-) ions are in a dynamic equilibrium. This equilibrium is pushed towards dichromate by lowering the pH - a classic demonstration of Le Chatelier's principle.
Chromates and Dichromates are salts of chromic acid and dichromic acid, respectively.
The chromium atoms are in oxidation state +6 in both, and the chromate and dichromate ions are fairly strong oxidizing agents.
Most chromate and dichromate salts of heavy metals, lanthanides or alkaline earth metals are only very slightly soluble in water and are thus of much less usefulness.
Chromium intensification uses potassium dichromate together with equal parts of concentrated hydrochloric acid diluted down to approximately 10% vol to vol to treat weak and thin negatives of fl and white film.
All the gelatine exposed to sun-light will have been hardened by the dichromate and will be retained on the screen leaving a precise mask of the required design which can be printed in the usual way.
Potassium dichromate is one of the most common culprits in causing chromium dermatitis.
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