Colourless, crystalline, toxic carboxylic acid found in many plants, especially rhubarb, wood sorrel, and spinach.
Because it forms soluble chelate s with iron, some of the iron in these plants is not available nutritionally. However, this property makes it useful for removing blood and rust stains, cleaning metals other than iron, and flushing car radiators. Oxalic acid and its salt s (oxalates) are used in many chemical processes.