They may be prepared by the dry distillation of the ammonium salts.
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.
Cobalt ammonium phosphate, CoNH4PO 4.12H 2 0, is formed when a soluble cobalt salt is digested for some time with excess of a warm solution of ammonium phosphate.
By dry distillation it gives ammonium cyanide.
It may be obtained in the spongy form by igniting iridium ammonium chloride, and this variety of the metal readily oxidizes when heated in air.