In contrast to other multicomponent systems involving ammonium dihydrogenphosphate, the NH₄⁺, Na⁺ || H₂PO₄^–, NO₃^– - H₂O system has been studied in detail. Shpunt^1-3 determined solubility isotherms of this system at 253 K, 258 K, 263 K, 273 K, 293 K and 303 K and also made a polythermal investigation of the stable diagonal NH₄H₂PO₄ - NaNO₃ - H₂O system. Figure 21, Fig. 22, Fig. 23, and Fig. 24 show a comparison of some of these solubility values with those reported earlier by Shpunt⁷ as well as results reported by other investigators who studied the boundary ternary systems,^4,5,7,8 (see pp 1343, 1351). It is obvious that the agreement is not very good even with results reported by a given author. Consequently, nothing definitive can be said about the shape of the respective phase diagram at this time.

Experimental Data:   (Notes on the Nomenclature)