Phosphorus oxynitride glasses containing M2O, MO and M2O3 were prepared by melting in dry ammonia. The glass composition and the water content in the furnace atmosphere were factors controlling the maximum nitrogen dissolution in a phosphate glass. For the same cation concentration in a phosphate glass, the amount of nitrogen that could be dissolved decreased with increasing cation valence. Other properties evaluated included the thermal expansion coefficient and the dissolution rate in water.