Polysulphides of Calcium

If calcium sulphide and sulphur are boiled together with water they dissolve, forming yellow-red solutions which are considered to contain CaS₅, CaS₄, and probably CaS₂. Poly-sulphides, along with calcium thiosulphate, are also formed by boiling together lime and sulphur in water for the production of a lime-sulphur spray as an insecticide for animals and plants, especially in the Pacific States.

Auld concluded, from experiments on the action of dilute acids, that poly sulphides of sulphur content at least as high as CaS₇ were formed, and suggested that the constitution is represented by the formula ..., the sulphur atoms in the chain becoming progressively more loosely attached.

Barbieri fixed the polysulphides with hexamethylenetetramine and then determined their composition. He obtained the compounds CaS₅.10H₂O.2C₆H₁₂N₄ and CaS₄.10H₂O.2C₆H₁₂N₄, and concluded that CaS₅ is formed by saturating calcium hydrosulphide with sulphur, and CaS₄ by boiling sulphur with lime.

Solutions of polysulphides readily hydrolvse, producing calcium hydroxide, sulphur, and sulphuretted hydrogen.

A compound containing polysulphides, and known as " liver of sulphur," is obtained by calcining together equal weights of calcium oxide and sulphur.