(2) A modification of (1), followed by Guignet, was to replace the bichromate of potash by chromate of soda, prepared by dissolving in boiling water 61 parts of neutral chromate of potash and 53 parts of nitrate of soda. For the neutral chromate of potash, also, may be substituted a mixture of 92 parts of bichromate of potash and 89 parts of crystallised carbonate of soda, the nitrate of soda remaining as before. On cooling, in either case, the solution deposits much nitrate of potash, which is commercially valuable. The chromate of soda present in the mother liquors is obtained by evaporating to dryness. The pigment produced by the chromate of soda process is lighter in colour than that obtained with bichromate of potash. It may be still further paled by adding a little alumina, baryta, or other white pigment to the bichromate and boracic acid mixture before calcining. (3) Equal quantities of potash bichromate and potato starch are thoroughly mixed and then calcined in a crucible at a high temperature. The product is washed with boiling water, to remove the potash carbonate formed, and any remaining undecomposed bichromate. The precipitated chromium oxide is filtered, dried, and again calcined to drive off the water. The final result is a handsome pigment which flows well from the brush. (4) On heating in a crucible a mixture of 3 parts of neutral chromate of potash with 2 parts of salammoniac, the two salts are decomposed, the result being formation of chromium oxide mixed with potassium chloride, which latter is removed by several washings with hot water. The brilliancy of the chromium oxide is enhanced by calcination at a dull red heat. (5) Fuse together 3 parts of boracic acid and 1 part of potash bichromate at a dull red heat on the hearth of a reverberatory furnace. Thus is formed a borate of chromium and potash, with evolution of oxygen. The mass is repeatedly washed with boiling water, which causes decomposition, and consequent separation of hydrated oxide of chromium, and a soluble borate of potash. The chromium oxide is washed, and ground very fine. (6) When a solution of potash bichromate is poured into a neutral solution of mercury proto-nitrate, it forms an orange-coloured precipitate, which is washed and gently dried, then powdered, and heated in a stoneware retort provided with an arm dipping into cold water, by which the mercury is distilled and condensed. The residue in the retort is a highly comminuted chromium oxide, of a fine dark-green colour. (7) On calcining potash bichromate in a crucible at a very high temperature, it is decomposed, and results in chromium oxide and potash, the latter of which can be washed out. The chromium oxide thus obtained is very dense and of a dark-green colour resembling (6).