Blowpipe Test with Cobalt Nitrate

Light colored and infusible aluminium minerals when moistened with a drop of cobalt nitrate and heated intensely before the blowpipe assume a dark blue color.  Zinc silicates will also yield a blue color under similar conditions. Blowpipe Test with Cobalt Nitrate Procedure:

1.    Oxide Coating on Charcoal.  When an antimony mineral is heated in the oxidizing flame on charcoal, a heavy white coating of antimony oxide settles on the charcoal at a short distance from the mineral.  The coating is readily volatile when heated.

2.    Open Tube Test.  When metallic antimony or a compound of antimony with sulphur is heart in the open tube, a white powdery sublimate of antimony oxide, Sb₂O₃, forms in a ring on the inner wall of the tube.  It is another oxide of antimony, Sb₂O₄.  It is non-volatile and is usually more conspicuous than the first.

3.    Sublimate on Plaster Tablet. Mixed with a mixture of potassium iodide and sulphur yields in the oxidizing flame an orange to red sublimate of SBI₃.