SCHLIPPE'S SALT, or sodium thioantimoniate, Na3SbS4·9H2O, named after K. F. Schlippe (1799–1867), is prepared by dissolving the calculated quantities of antimony trisulphide, sulphur and sodium hydroxide in water, or by fusing sodium sulphate (16 parts), antimony sulphide (13 parts) and charcoal (4.5 parts), dissolving the melt in water and boiling the solution with 2½ parts of sulphur. The liquid is then filtered and evaporated. The salt crystallizes in large tetrahedra, which are easily soluble in water, and have a specific gravity 1.806. The anhydrous salt melts easily on heating, and in the hydrated condition, on exposure to moist air becomes coated with a red film. It combines with sodium thiosulphate to form Na3SbS4·Na2S2O3·2OH2O.