The influence of the period of sulphite cooking upon the strength of pulp was investigated. The cooked samples were taken out from the digestor by means of a copper pipe, attached to the central position of the digestor wall, (1) one hour before the commencement of gas recovery, (2) at the time when the gas recovery began, (3) 30 minutes after the gas recovery began. The samples, which were about 300500g, were washed with water, beated by ball mill, and made into the sheet by a small deckle box, and the strength of the sheet as well as the bleaching property of the pulp were examined. The results of the experiments were as follows :
(1) When the cooking temperature is raised rapidly above 100°C in the beginning of the digestion, the pulp produced is of an inferior strength.
(2) When the temperature is kept lower in the later stage of cooking, the strength of pulp becomes higher and the bleaching property becomes better, though the cooking hour is prolonged.
(3) The lowering of pressure at the end of cooking produces an easy bleaching pulp, though a longer cooking is required.
(4) The strength of pulp is inversely proportional to the easiness of bleaching.
(5) The strength of pulp is decreased as the cooking is prolonged.

View full abstract