Ammonium bisulfate, also known as ammonium hydrogen sulfate, is a white, crystalline solid with formula (NH4)HSO4. It is the product of the half-neutralization of sulfuric acid by ammonia.
A 2038 (OTTO) Ammonium bisulphate, 98% Cas 7803-63-6 - used as a weaker alternative to sulfuric acid, although sodium bisulfate is much more common.