. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. to aconsiderable extent. However, its bleaching action is not perma-nent; the stock tends to revert to its former color, because S02isareducing agent, and compounds reduced by it may be re-oxidizedby the air. It will be perceived that the chemical action of 28 BLEACHING OF PULP §9 sulphur dioxide is just the opposite of that of bleaching powder,which is an oxidizing agent. 44. Bleaching of Sulphate Pulp.—Sulphate, or kraft, pulp isvery difficult to bleach; it is usually made primarily for mea
. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. to aconsiderable extent. However, its bleaching action is not perma-nent; the stock tends to revert to its former color, because S02isareducing agent, and compounds reduced by it may be re-oxidizedby the air. It will be perceived that the chemical action of 28 BLEACHING OF PULP §9 sulphur dioxide is just the opposite of that of bleaching powder,which is an oxidizing agent. 44. Bleaching of Sulphate Pulp.—Sulphate, or kraft, pulp isvery difficult to bleach; it is usually made primarily for means raw cooking, to begin with, and any under-cookedpulp is hard to bleach. In order to bleach the usual sulphate pulp, large quantities ofbleach and high temper-atures afrre result of this is, ofcourse, very drastic ac-tion on the cellulose anda weakened presence of a largequantity of shives inunder-cooked pulp is oneof the main sources of dif-ficulty. Very little sul-phate stock is bleachedin America at the present3 time, but bleached sul- Layer of Fblp. Fig. 8. Lap rabie pnate jg regularly quotedin European markets. 45. Bleaching ofGround Wood.—Thebleaching of groundwood is accomplishedby use of sodium bisul-phite solution action is similarto that of sulphur dioxide—a direct chemical reducing action onthe wood, which alters its color. In order to bleach ground wood, the solution of bleaching agentmust be very strong; it cannot, therefore, be done in the ordinarystock vat, where much water is necessarily present. Fig. 8shows one type of apparatus. A lead-lined trough T, one longedge rolled, is placed just over the distributing roll D of a wetmachine. A strip of felt is laid over one edge of the trough,parallel to the roll D; one edge of the felt dips into the trough T,and the other hangs down 3 or 4 inches over the lip, touching §9 BLEACHING THE STOCK 29 the roll D. The trough T is filled with a 30% solution of sodiumbisulphite, whi
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaperma, bookyear1921
