A small loop is made in the end of a platinum wire (as used in the flame test) and heated in a Bunsen flame until red hot. It is then dipped into powdered borax, and the adhering solid is held in the hottest part of the flame where it swells up as it loses its water of crystallization and then shrinks, forming a colourless, transparent glass-like bead (a mixture of sodium metaborate and boric anhydride),
The bead is moistened (traditionally with the tongue) and dipped into the sample to be tested such that only a tiny amount of the substance adheres to the bead. If too much substance is used, the bead will become dark and opaque. The bead and adhering substance is then heated in the lower, reducing, part of the flame, allowed to cool, and the colour observed. It is then heated in the upper, oxidising, part of the flame, allowed to cool, and the colour observed again.
Characteristic coloured beads are produced with salts of copper, iron, chromium, manganese, cobalt and nickel. After the test, the bead is removed by heating it to fusion point, and jerking it into a vessel of water.
|Reducing flame||Oxidising flame||Metal|
|Colourless when hot; opaque red when cold||Green when hot; blue when cold||Copper (Cu)|
|Green, hot and cold||Yellow, hot and cold||Iron (Fe)|
|Green, hot and cold||Dark yellow when hot; green when cold||Chromium (Cr)|
|Colourless, hot and cold||Violet, hot and cold||Manganese (Mn)|
|Blue, hot and cold||Blue, hot and cold||Cobalt (Co)|
|Grey when cold||Reddish-brown when cold||Nickel (Ni)|
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