Cobalt is a chemical element with symbol Co. It is found in various salts like cobalt chloride, cobalt nitrate and cobalt carbonate as Co (II) ion. Cobalt based blue pigments, cobalt blue, have been used for jewellery and paints and to impart distinctive blue tint to glass. In group IV, cobalt ions are precipitated as their sulphides by passing hydrogen sulphide gas through their solution. Cobalt ion reacts with potassium nitrite in presence of acetic acid to form yellow precipitate of Potassium cobaltinitrite. It also reacts with ether and a crystal of ammonium thiocyanate, to form blue coloured ammonium cobalti thiocyanate, which is obtained in the ethereal layer.
This video explains how to test for the presence of cobalt ion in a given salt.