a white or gray crystalline salt, with a slight alkaline taste, used as a flux, in soldering metals, making enamels, fixing colors on porcelain, and as a soap. it occurs native in certain mineral springs, and is made from the boric acid of hot springs in tuscany. it was originally obtained from a lake in thibet, and was sent to europe under the name of tincal. borax is a pyroborate or tetraborate of sodium, na2b4o7.10h2o.