Phosphorous acid is not derived from potash. Phosphorous acid is a chemical compound with the formula H3PO3. It is a weak diprotic acid that can lose one or two protons to form dihydrogen phosphate (H2PO3-) or hydrogen phosphate (HPO32-). Phosphorous acid is not a naturally occurring substance, but it can be produced by the hydrolysis of phosphorus trichloride. Potash, on the other hand, is a potassium-containing salt that can be found in nature or extracted from minerals such as sylvite or carnallite.