Sodium Chromisilicates

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.