Containing two molecules of oxalic acid is a colorless crystalline columnar crystals of water, especially the herbaceous plants usually have the ingredients, mostly in the form of potassium or calcium salts. Begonia, banana in the free acid form. 

 Oxalic acid, also known as oxalic acid, is the simplest dicarboxylic acid. Formula (COOH) 2 ? 2H2O, used primarily as a reducing agent and bleaching agent, manufacturing oxalate, is also used for the purification of rare metals, antibiotics and organic synthesis purification.