Ordinary superphosphate run through 20 - 40 - 60 - 100 and plus mesh sieves were treated with 3 per cent (weight basis) of anhydrous ammonia in special aparattus. This amount reacting with normal superphosphate caused reversion in water soluble phosphate. The rate of ammoniation varied from 2,7 to 3,8% per unit of P2O5 considering the fraction before the treatment. The reversion range was from 44,6 to 57,9% of water soluble phosphate. The rate of correlation between solubility and ammonia dosis was -0,96 and the linear regression obtained was Y = 24,344-4,732x.