It is a crystalline compound of boric acid and boron trioxide dissolved in water, which belongs to inorganic acid, mainly including tetraborate H2B4O7 (also called pyroboric acid), metaboric acid (HBO2)n and orthoboric acid H3BO3 (also called orthoboric acid). Among them, n-boric acid has the most water content and is the most stable. Boric acid, also referred to as boric acid for short, is white powdery crystal or scaly crystal with triclinic axis, which is shiny. It has a slight bitter taste. There is a greasy feeling in contact with the skin. It is odorless, soluble in water, ethanol, glycerin, ethers and essential oils, and the aqueous solution is weakly acidic. When the boric acid is heated to 70-100℃, it gradually dehydrates into metaboric acid Chemicalbook, becomes pyroboric acid at 150-160℃ and becomes boric anhydride (B2O3) at 300℃. Boric acid is toxic to human body. Solubility in water: 2.77 at 0℃, 3.65 at 10℃, 4.87 at 20℃, 5.74 at 25℃, 6.77 at 30℃, 8.90 at 40℃, 11.39 at 50℃, 14.89 at 60℃, 23.54 at 80℃. The weak acidity of aqueous solution is a typical Lewis acid, which can promote its solubility in water in the presence of hydrochloric acid, citric acid or tartaric acid. Therefore, it can be purified by recrystallization.