Borax (from Persian burah[1][2]), also called sodium borate, or sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.

Borax has a wide variety of uses. It is a component of many detergents, cosmetics, and enamel glazes. It is also used to make buffer solutions in biochemistry, as a fire retardant, as an anti-fungal compound for fiberglass, as an insecticide, as a flux in metallurgy, and as a precursor for other boron compounds

Sodium borate is used in biochemical and chemical laboratories to make SB buffers, e.g. for gel electrophoresis of DNA. It has a lower conductivity, produces sharper bands, and can be run at higher speeds than can gels made from TBE buffer or TAE buffer (5 - 35 V/cm as compared to 5 - 10 V/cm). At a given voltage, the heat generation and thus the gel temperature is much lower than with TBE or TAE buffers, therefore the voltage can be increased to speed up electrophoresis so that a gel run takes only a fraction of the usual time. Downstream applications, such as isolation of DNA from a gel slice or southern blot analysis, work as expected with sodium borate gels. Borate buffers (usually at pH₈) are also used as preferential equilibration solution in DMP-based crosslinking reactions.

Lithium borate is similar to sodium borate and has all of its advantages, but permits use of even higher voltages due to the lower conductivity of lithium ions as compared to sodium ions._[3] However, lithium borate is much more expensive.

A mixture of borax and ammonium chloride is used as a flux when welding iron and steel. It lowers the melting point of the unwanted iron oxide (scale), allowing it to run off. Borax is also used mixed with water as a flux when soldering jewelry metals such as gold or silver. It allows the molten solder to flow evenly over the joint in question. Borax is also a good flux for 'pre-tinning' tungsten with zinc - making the tungsten soft-solderable._[4]