Hydroxylamine-O-sulfonic acid (HOSA) or aminosulfuric acid is the inorganic compound with molecular formula HNOS that is formed by the sulfonation of hydroxylamine with oleum.  It is a white, water-soluble and hygroscopic, solid, commonly represented by the condensed structural formula HNOSOH, though it actually exists as a zwitterion and thus is more accurately represented as HNOSO.  It is used as a reagent for the introduction of amine groups (&ndash;NH), for the conversion of aldehydes into nitriles and alicyclic ketones into lactams (cyclic amides), and for the synthesis of variety of nitrogen-containing heterocycles.