Borax

Borax, $Na_2B_4O_7 \cdot 10H_2O$

Borax is the single most important compound of boron. It is a white crystalline solid usually written as $Na_2B_4O_7 \cdot 10H_2O$, but this formula is a simplification: the real species present is the tetranuclear anionic unit $[B_4O_5(OH)_4]^{2-}$, so the more accurate formula is $Na_2[B_4O_5(OH)_4] \cdot 8H_2O$.

In water, borax dissolves to give an alkaline (basic) solution and, on hydrolysis, liberates orthoboric acid:

On heating, borax first loses its water of crystallisation and swells up; further heating melts it to a clear liquid that solidifies on cooling into a glassy bead known as a borax bead:

(sodium metaborate + boric anhydride) …