Cobaltic Fluoride, CoF₃

Cobaltic Fluoride, CoF₃, may be prepared by electrolysing a saturated solution of cobaltous fluoride in 40 per cent, hydrofluoric acid contained in a platinum dish which serves as anode, the cathode being a platinum wire. It is deposited as a green powder which does not redissolve on stopping the current. In air it slowly turns grey, then red. Water readily decomposes it, yielding cobaltic hydroxide. The salt dissolves in concentrated sulphuric acid, giving a brown solution which becomes green on dilution, and red when gently warmed.