Oxalic acid, adipic acid, the simplest dicarboxylic acid. The structural Jane style HOOCCOOH. It is colorless transparent crystal, harmful, cause the body's pH out of balance, affect children's development, the oxalic acid plays an important role in industry, oxalic acid can rust. Oxalic acid are found in nature, often in the form of oxalate present in plants such as barberry, Rumex grass, wood sorrel and sorrel grass of the cell membrane, almost all plants contain calcium oxalate