Thio-compounds are known, analogous to these salts. Mention may be made of mixed oxy-thio-phosphates, e.g. Na3PO3S and Na3POS3, which result from the action of alkaline hydroxides on phosphorus penta-sulphide, a grey solid produced by direct combination of phosphorus with sulphur. They are easily decomposed by hot water; hence the thio-arsenates and the thio-antimonates are better known. Arsenious sulphide, As2S8, a yellow precipitate formed by the action of hydrogen sulphide on a solution of arsenious chloride, and antimony trisulphide, Sb9S3, an orange precipitate similarly formed, dissolve in solutions of poly-sulphides of t he alkalies; these solutions, on evaporation, deposit crystals on cooling : As2S3 = 2K2Si.Aq = 2K3AsS4.Aq + S(n_2). Sodium thio-antimonate, Na3SbS4.9H2O, has long been known as "Schlippe's salt." One of the sulphur atoms may be replaced by selenium, giving Na3SbS3Se-9H2O, thus showing the similarity in character between sulphur and selenium.