A compound of soda and boracic acid, and of considerable use in various metallurgic operations. It enters into the composition of reducing fluxes, and is of the greatest use in analysis by the blow-pipe. It is more especially used in soldering; it assists the fusion of the solder, causes it to flow, and keeps the surface of the metal in a soft clean state, which facilitates the operation. It may also be applied with advantage in glass manufactories; for when the fusion turns out bad, a small quantity of borax re-establishes it