Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is a compound with formula Na2H4B4O9•nH2O or, more precisely, [Na•(H2O)m]2 [B4O5(OH)4]. The formula is often improperly written as Na2B4O7•(n+2)H2O, reflecting an older incorrect understanding of the anion's molecular structure. The name may refer to any of a number of closely related boron-containing mineral or chemical compounds that differ in their water of crystallization content. The most commonly encountered one is the octahydrate Na2H4B4O9•8H2O or [Na(H2O)4]2 [B4O5(OH)4] (or Na2B4O7•10H2O, the "decahydrate", in the older notation). It is a colorless crystalline solid that dissolves in water. Borax is a component of many detergents, cosmetics, and enamel glazes. It is used to make buffer solutions in biochemistry, as a fire retardant, as an anti-fungal compound, in the manufacture of fiberglass, as a flux in metallurgy, neutron-capture shields for radioactive sources, a texturing agent in cooking, as a cross-linking agent in slime, as an alkali in photographic developers, as a precursor for other boron compounds, and is useful as an insecticide (similarly to boric acid). In artisanal gold mining, borax is sometimes used as part of a process (as a flux) meant to eliminate the need for toxic mercury in the gold extraction process, although it cannot directly replace mercury. Borax was reportedly used by gold miners in parts of the Philippines in the 1900s. Borax was first discovered in dry lake beds in Tibet and was imported via the Silk Road to the Arabian Peninsula in the 8th century AD. Borax first came into common use in the late 19th century when Francis Marion Smith's Pacific Coast Borax Company began to market and popularize a large variety of applications under the 20 Mule Team Borax trademark, named for the method by which borax was originally hauled out of the California and Nevada deserts.
