They are precipitated from their alkaline solutions as cobalt sulphide by sulphuretted hydrogen, but this precipitation is prevented by the presence of citric and tartaric acids; similarly the presence of ammonium salts hinders their precipitation by caustic alkalis.
Certain yeasts exercise a reducing action, forming sulphuretted hydrogen, when sulphur is present.
It combines with sulphuretted hydrogen, in the .presence of water, to form the compound C 2 N 2 H 2 S, and in the presence of alcohol, to form the compound C 2 N 2.2H 2 S.
By the addition of sulphuretted hydrogen to the nitriles, or by the action of phosphorus pentasulphide on the acid-amides.
It forms slightly coloured small crystals possessing a strong disagreeable smell, and is rapidly decomposed by water with the formation of boric acid and sulphuretted hydrogen.