Boric acid is actually the hydrate of boron oxide (B203 ~ 3H20), which is a triclinic crystal powder with pearl luster. It has a smooth feel and no odor when contacting the skin. Soluble in water, the aqueous solution is weakly acidic. The solubility in water increases with the increase of temperature, and can be volatilized with water vapor, and the solubility in inorganic acid is smaller than that in water. Also soluble in alcohol, glycerin, ethers and essential oils. Density 1.435 g/cm 3 (15 ° C). When heated to 70 ~ 100℃, metaborate is gradually dehydrated to form metaborate, pyroboric acid is formed at 150 ~ 160℃, and boric anhydride (B203) is formed at 300℃.