The batch ammoniation of superphosphate, as was commonly practiced in the 1930’s and 1940’s, sometimes resulted in partial granulation of the reaction mass. Investigators then determined the physical and chemical parameters for granulation so that processing methods could be developed to provide consistent granulation of fertilizers. Introduction of the rotary drum continuous ammoniator in the 1950’s was a result. The mechanism of the agglomeration and the sources of liquid phase for granulation are described. The effect of temperature upon the quantity of liquid phase and the thermal chemistry of the major chemical reactions of ammoniation and neutralization is reviewed. The role of the formulator is to establish ideal conditions for agglomeration in addition to providing the guaranteed plant food ingredients for any given fertilizer product. Finally, the effect of ammoniator drum dimensions on optimizing the product output for any given formulation is investigated.