Sodium tetraborate decahydrate, also known as sodium pyroborate, CAS number [1303-96-4], molecular formula Na2B4O7·10H2O, molecular weight 381.37, colorless translucent crystal or white crystalline powder, monoclinic crystal system. It is odorless, salty, soluble in water and glycerin, insoluble in ethanol and acid, and the aqueous solution is weakly alkaline. It has a density of 1.73g/cm3 and is weathered in dry air. When the temperature is higher than 56℃, the pentahydrate salt is precipitated from the solution. When the temperature is lower than 56℃, the decahydrate salt is precipitated. When heated to 350 ~ 400℃, complete water loss becomes anhydrous salt; It is heated to 878 ° C and melts into glass. Molten borax can dissolve many metal oxides, producing a double salt of metaboric acid with a characteristic color, and this property of borax is known as the “borax bead test”.