4. A PROCESS FOR THE PREPARATION OF A SUBSTANTIALLY NON-CAKING CRYSTALLINE COMPOSITION CONTAINING SALT SELECTED FROM THE GROUP CONSISTING OF AMMONIUM SULPHATE, POTASSIUM SULPHATE, AND MIXTURES THEREOF, WHICH COMPRISES INCORPORATING THEREIN IN A MIXING ZONE AN AMOUNT OF FROM 0.0001% TO 0.1% BY TOTAL WEIGHT OF SALT OF AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF CERIC SULPHATE, CERIC OXIDE, CERIC HYDROXIDE, CEROUS NITRATE, AMMONIUM CERIC SULPHATE AND AMMONIUM CERIC NITRATE.