1. A PROCESS FOR CRYSTALLIZING SOLUTIONS DEVELOPING GASES WHEN SUBJECTED TO A VACUUM, SAID PROCESS COMPRISING THE STEPS OF CONTINUOUSLY FEEDING A SOLUTION THROUGH A PREEVAPORATOR TO A CRYSTALLIZER IN BOTH OF WHICH A VACUUM IS MAINTAINED, CONTINUOUSLY WITHDRAWING THE CRYSTAL SLURRY FORMED INTHE CRYSTALLIZER, PASSING A PORTION OF THE CRYSTAL SLURRY TO A CLASSIFIER TO SEPARATE SAID SLURRY INTO FINE AND COARSE FRACTIONS, SUPPLYING A PORTION OF THE COARSE FRACTION TO THE PRE-EVAPORATOR, AND MIXING THE COARSE FRACTION WITH THE SOLUTION TO BE CRYSTALLIZED IN THE PRE-EVAPORATOR WHILE MAINTAINING THE ABSOLUTE PRESSURE IN THE PREEVAPORAATOR GREATER THAN THAT IN THE CRYSTALLIZER TO AN EXTENT THAT NO CRYSTALLIZATION OF THE SOLUTION TAKES PLACE IN THE PRE-EVAPORATOR.