It is used for the detection of coloured basic radicals under the name borax bead test.

Borax bead test : Borax bead is a mixture of NaBO₂ and B₂O₃. B₂O₃ on heating combines readily with a number of coloured transition metal oxides such as Co, Ni, Cr, Cu, Mn, etc. to form the corresponding metaborates which possess characteristic colours,

                      

Colours of some important metaborates are : Cupric metaborate, Cu (BO₂)₂ is dark blue, chromium metaborate, Cr (BO₂)₂ is green, nickel metaborate, Ni(BO₂)₂ is brown and manganese metaborate, Mn(BO₂)₂ is pink violet.

When heated with C₂H₅OH and conc. H₂SO₄ it gives volatile vapours of triethyl borate which burns with a green edged flame.

Na₂B₄O₇ + H₂SO₄ + 5H₂O ——→ Na₂SO₄ + 4H₃BO₃

This reaction is used as a test for borate radical in qualitative analysis.

Uses : (a) In making optical and hard glasses. (b) In the laboratory for borax bead test. (c) In softening of water. (d) In the preparation of medicinal soaps due to its antiseptic character.