Borax is widely used in qualitative analysis, since it gives coloured beads with transition
metal salts. The chemistry o f the borax bead test is as follows:
$Na _{2} B _{4} O _{7} \cdot 10 H _{2} O \to Na _{2} B _{4} O _{7}+ 10H _{2} O $
$Na _{2} B _{4} O _{7} \ce{->[{740^{\circ}}]} $ $2 N a B O_{2}+B_{2} O_{3} $
$\underbrace{\text { sod. metaborate boric anhydride }}_{\text {Glassy bead }}$
$CuSO _{4}+ B _{2} O _{3} \longrightarrow CuO \cdot B _{2} O _{3}+ SO _{3}$
Thus coloured beads are formed due to the formation of metal metaborates.