use of a heat exchange hopper for cooling the granules the following examples illustrate the invention without however limiting the scope thereof for the general modus operandi reference will be made to the above mentioned french patents examples 1 to 4 relate to the first variant and i and ii to the second variant of the invention incorporate successively the sodium bicarbonate the citric acid and the glycocoll switch on the turbine of the granulator at an output allowing fluidization of the powders the solvent is always sprayed on the powders in suspension in air which makes it possible to increase the exchange surface between the base particles and the acid particles at this stage of operation the output and spray time must be monitored the rate of flow of air is to be monitored so as to avoid too great a turbulence of the powders in the cavity of the apparatus which would render the particles fragile granulation on granulator drier of an effervescent mixture containing a plurality of active principles ______________________________________formula of granulation______________________________________paracetamol 28 kgmonosodium carbonate 100 kgmonopotassium carbonate 3 740 kgsorbitol 25 500 kganhydrous citric acid 73 000 kgascorbic acid 17 000 kgtotal 247 24 kg______________________________________ for the following two examples operation is carried out as in examples 1 and 2 from the formulations hereinbelow ______________________________________disodium sulfate.