Methods of isotope concentration

Claim 1

IN A METHOD OF PREPARING A FLUID SUBSTANCE ENRICHED IN DEUTERIUM BY EXCHANGE OF DEUTRERIUM BETWEEN A PRINCIPAL FLUID HYDROGEN-CONTAINING SUBSTANCE TO BE ENRICHED AND AN AUXILIARY HYDROGEN-CONTAINING SUBSTANCE IN THE GASEOUS PHASE, BOTH SUBSTANCE CONTAINING DEUTERIUM, IN A CASCADE SYSTEM OF INTERCONNECTED STAGES, WHEREIN EACH STAGE COMPRISES TWO EXCHANGE COLUMNS MAINTAINED AT DIFFERENT TEMPERATURES THROUGH EACH OF WHICH COLUMNS SAID TWO SUBSTANCES FLOW IN CONTERCURRENT AND INTERMINGLE SO THAT SAID PRINCIPLE SUBSTANCE IS ENRICHED IN ONE COLUMN AND IMPOVERISHED IN THE OTHER, WHEREIN A PROPORTION OF THE PRINCIPAL SUBSTANCE FLOWING THROUGH EACH STAGE EXCEPT THE LAST IS WITHDRAWN BETWEEN THE EXCHANGE COLUMNS AND PASSED TO THE ENRICHING COLUMN OF THE NEXT SUCCEEDING STAGE, THE PRINCIPAL SUBSTANCE FLOWING FROM THE IMPROVERISHING COLUMN OF EACH STAGE EXCEPT THE FIRST BEING RETURNED TO THE ENRICHING COLUMN OF THE NEXT PRECEEDING STAGE, THE PRINCIPAL SUBSTANCE BEING FED INTO AND WITHDRAWN FROM THE FIRST STAGE AND THE PRINCIPAL SUBSTANCE ENRICHED IN DEUTERIUM BEING WITHDRAWN AS PRODUCT BETWEEN THE COLUMNS OF THE LAST STAGE, THE IMPROVEMENT WHICH CONSISTS IN WITHDRAWING AUXILIARY SUBSTANCE IMPROVERISHED IN DEUTERIUM FROM THE ENRICHING COLUMN OF A STAGE NUMBERED N, RETURNING SAID AUXILIARY SUBSTANCE TO THE ENRICHING COLUMN OF A STAGE NUMBERED N-P (P BEING AN INTEGER SMALLER THAN N AND GREATER THAN 1), WHILE WITHDRAWING AUXILIARY SUBSTANCE ENRICHED IN DEUTERIUM FROM STAGE N-P AND RETURNING IT TO THE IMPOVERISHING COLUMN OF STAGE N.