Process of manufacturing pulp from cellulosic fibrous materials

Claim 1

AN IMPROVED THREE-PHASE MANUFACTURING PROCESS FOR THE PRODUCTION OF PULP FROM CELLULOSIC FIBROUS MATERIAL WHICH COMPRISES MAKING CHIPS OF CELLULOSIC FIBROUS MATERIAL, DIGESTING AS A FIRST PHASE SAID CHIPS IN A DIGESTER IN A WEAK ACID COOKING LIQUOR CONSISTING ESSENTIALLY OF A BISULFITE OF THE GROUP CONSISTING OF SODIUM, POTASSIUM AND AMMONIUM AND CONTAINING AN EXCESS OF SULFUR DIOXIDE, THE SAID WEAK ACID LIQUOR HAVING A TOTAL SULFUR DIOXIDE CONTENT OF ABOUT 5% TO ABOUT 10%, A COMBINED SO2 CONTENT OF ABOUT 0.05% TO ABOUT 1.5%, AND A FREE SO2 CONTENT OF ABOUT 4.25% TO ABOUT 8.5%, MAINTAINING A DIGESTING PRESSURE WITHIN SAID DIGESTER OR ABOUT 75 TO ABOUT 150 POUNDS PER SQUARE INCH, CONTINUING THE WEAK ACID DIGESTING FOR ABOUT 3 HOURS WHILE RAISING THE TEMPERATURE TO ABOUT 100* C. TO PRODUCE PARTLY DIGESTED PULP AND TO REDUCE THE SULFUR DIOXIDE CONTENT TO LESS THAN ABOUT 1%, INCREASING THE TEMPERATURE TO WITHIN A RANGE OF ABOUT