Moissan (Comptes rendus, 1893, 116, p. 349; 1894, 119, p. 185) reduces the sesquioxide with carbon, in an electric furnace; the product so obtained (which contains carbon) is then strongly heated with lime, whereby most of the carbon is removed as calcium carbide, and the remainder by heating the purified product in a crucible lined with the double oxide of calcium and chromium.
Chromic chloride, CrC1 31 is obtained in the anhydrous form by igniting a mixture of the sesquioxide and carbon in a current of dry chlorine; it forms violet laminae almost insoluble in water, but dissolves rapidly in presence of a trace of chromous chloride; this action has been regarded as a catalytic action, it being assumed that the insoluble chromic chloride is first reduced by the chromous chloride to the chromous condition and the original chromous chloride converted into soluble chromic chloride, the newly formed chromous chloride then reacting with the insoluble chromic chloride.
Various other oxides of chromium, intermediate in composition between the sesquioxide and trioxide, have been described, namely chromium dioxide, Cr203 Cr03, and the oxide Cr03.2Cr203.
It is also obtained by passing chlorine into a suspension of lead oxide or carbonate, or of magnesia and lead sulphate, in water; or by treating the sesquioxide or red oxide with nitric acid.
The ore generally occurs in the form of oxides, manganite and pyrolusite, and contains a high percentage of sesquioxide of manganese.
Chromium sesquioxide is a basic oxide, although like alumina it acts as an acid-forming oxide towards strong bases, forming salts called chromites.
Bismuth and antimony give (the latter very readily) sesquioxide (Bi 2 O 3 and Sb203, the latter being capable of passing into Sb204).
Thechromites maybe looked upon as salts of chromium sesquioxide with other basic oxides, the most important being chromite (q.v.).
Goldschmidt (Annalen, 1898, 301, p. 19) in which the oxide is reduced by metallic aluminium; and if care is taken to have excess of the sesquioxide of chromium present, the metal is obtained quite free from aluminium.
Yet, unlike potassium or lead, it forms a feebly basic sesquioxide similar to manganic oxide, Mn203.