Qualitative analysis method. Dip a little borax (Na2B4O7. 10H2O) in the platinum wire coil, burn and melt to generate colorless glassy beads, then dip a little powder or solution of the sample to be tested, and continue to burn, the beads will show different colors, so that the existence of some metal elements can be detected. This method makes use of the characteristic that molten borax can form various color compounds with oxides and salts of most metal elements. For example, the borax beads of iron are yellow after being burned by oxidation flame and green after being burned by reducing flame. Submerged in different metal oxides, molten beads of different colors can be fired. Cr3+ is sapphire, Cr3+ is green, Ni2+ is red and Fe3+ is yellow, which can be used for qualitative analysis of metals.

Specific reaction equation

Na2B2O7+CoO= heating = 2nabo2 Co (Bo2) 2 (sapphire color)