Oxalic acid, << ok SAL ihk, >> is an organic acid found in many vegetables and other plants. It occurs abundantly as its potassium salt in the sap of dock and other plants in the oxalis and rumex plant groups. It is found in spinach, rhubarb, tomatoes, grapes, and sweet potatoes. Oxalic acid is also produced in the body. It has been known since early times.
Industry uses oxalic acid in processing textiles, bleaching straw hats, and removing paint and varnish. It is widely used in chemistry as an analytical reagent. Oxalic acid forms substances called complexes with various metals, especially iron. For this reason, it is also used as a rust and scale remover.
There are a number of processes for preparing oxalic acid. In one process, the acid forms from the oxidation of table sugar or other carbohydrates with nitric acid in the presence of a catalyst.
Oxalic acid occurs as clear, colorless crystals, soluble in water. It is highly poisonous if swallowed. The dihydrate form of oxalic acid melts at 101.5 °C (215 °F).
