By fusing together silica, sodium carbonate, and chromium sesquioxide with a large excess of sodium chloride, dark green orthorhombic and strongly pleochroic crystals, of composition 2Na2O.3Cr2O3.6SiO2, have been obtained. From a mixture of sodium metasilicate, chromic hydroxide, and excess of sodium chloride, rhombic crystals, of composition 5Na2O.2Cr2O3.11SiO2, resulted; while a mixture of ammonium dichromate, sodium metasilicate, and sodium chloride yielded crystals resembling tridymite, of composition 3Na2O.2Cr2O3.95SiO2. When the sodium salts were replaced by salts of other alkali metals or of the alkaline earth metals, analogous compounds were not obtained. A sodium chromisilicate, of composition Na20.Cr2O3.2SiO2 + (?)H2O, has also been described. Chromultramarine is a soft, light green powder, of composition Na2O(Al2O3.Cr2O3)2SiO2.4H2O, which, when boiled with sodium sulphide, gives ultramarine green.
Compounds, of composition 4(Na2O.Al2O3.2SiO2)Na2CrO4.5H2O and 5Na2O.4Al2O3.7SiO2.CrO3, have been obtained by heating a mixture of kaolin and sodium chromate with sodium hydroxide or carbonate. |