Borax is the most important compound of boron. It is a white crystalline solid of formula Na2B4O7.10H2O. in fact it contains the tetranuclear units [B4O5(OH)4]2-  and correct formula; therefore, is Na2[B4O5(OH)4]. 8H2O. borax dissolves in water to give an alkaline solution.

Na2B4O7  +  7H2O    →    2NaOH   +   4H3BO3
                                                           Orthoboric acid

On heating, borax first loses water molecules and swells up. On further heating it turns into a transparent liquid, which solidifies into glass like material known as borax bead.

Na2B4O7.10H2O(Heat)    →    Na2B4O7 (Heat)   →   2NaBO2    +    B2O3
                                                               Sodium  metaborate    Boric Anhydride
The metaborates of many transition metals have characteristic colors and, therefore, borax bead test can be used to identify them in the laboratory. For example, when borax is heated in a Bunsen burner flame with CoO on a loop of platinum wire, a blue colored Co(BO2)2 bead is formed.