The crude material (a Spanish phosphorite associated with quartz and other minerals), contained 48.5% of matter insoluble in hot dilute aquaregia (hereinafter referred to as'insolubles) and 20.5% P 0 1200 gm. of this material were ground to pass a screen of 80 mesh to the lineal inch and mixed with 1800 gm. of soft water to which sodium silicate (60 B.) was added at the rate of 2 lbs. per ton of crude material.