| Normal barium orthothioarsenate, Ba3As2S8.6H2O, is formed by the action of barium hydrosulphide on arsenic pentasulphide as faintly yellow, thick, transparent needles. It is only slightly soluble in water, by which it is decomposed. When it is heated, water of crystallisation is given off and the colour deepens. At higher temperatures it is decomposed. A pyrothioarsenate has been isolated. There are also oxy-compounds, for example Ba3(AsOS3)2.5H2O, and Ba3(AsO3S)2.6H2O, Ba3(AsO2S2)2.7H2O, and double salts, BaKAsS4.6H2O, BaNaAsO3S.9H2O, BaKAsOS3. 7H2O, and Ba7Na2As5S14O7.12H2O. |