Note 9 bis — Chapter XXI · CHROMIUM, MOLYBDENUM, TUNGSTEN, URANIUM, AND MANGANESE

We may conclude our description of tungsten and molybdenum by stating that their sulphur compounds have an acid character, like carbon bisulphide or stannic sulphide. If sulphuretted hydrogen be passed through a solution of a molybdate it does not give a precipitate unless sulphuric acid be present, when a dark brown precipitate of molybdenum trisulphide, MoS3, is formed. When this sulphide is ignited without access of air it gives the bisulphide MoS2; the latter is not able to combine with potassium sulphide like the trisulphide MoS3, which forms a salt, K2MoS4, corresponding with K2MoO4. This is soluble in water, and separates out from its solution in red crystals, which have a metallic lustre and reflect a green light. It is easily obtained by heating the native bisulphide, MoS2, with potash, sulphur, and a small amount of charcoal, which serves for deoxidising the oxygen compounds. Tungsten gives similar compounds, R2WS4, where R = NH4, K, Na. They are decomposed by acids, with the separation of tungsten trisulphide, WS3, and molybdenum trisulphide, MoS3. Rideal (1892) obtained W2N3 by heating WO3 in NH3. This compound exhibited the general properties of metallic nitrides.