Wikipedia
Disodium phosphate
Disodium phosphate (DSP), or sodium hydrogen phosphate, is the inorganic compound with the formula NaHPO. It is one of several sodium phosphates. The salt is known in anhydrous form as well as forms with 2, 7, 8, and 12 hydrates. All are water-soluble white powders; the anhydrous salt being hygroscopic.