3 58307 6 66 9 97 1 5 0 35 0 31 65 49 3 94 7 24 576 71 3 77308 6 66 9 92 1 5 0 35 0 61 65 88 4 35 7 57 576 83 3 77309 6 66 9 88 1 5 0 35 1 19 65 08 3 52 7 63 576 35 3 8310 6 66 8 94 1 5 0 35 2 39 64 82 3 26 7 95 576 4311 6 66 10 05 1 5 0 35 0 61 65 57 4 32 7 21 577 06 3 55sulfuric acid mixed in bisulfite312 6 66 10 08 1 5 0 35 0 33 64 02 2 92 8 27 577 96 4 061 hydrosulfiteref 313 6 8 6 76 0 0 0 65 53 3 3 10 577 14 4 95__________________________________________________________________________ bleaching trials were carried out on samples of thermo ground wood tgw pulp from a hydrosulphite bleach tower at a pulp mill in germany experience has shown that because of inferior wood quality during the summer months the initial iso brightness of unbleached tgw pulp is 2 to 3 points lower than during the rest of the year the target brightness can thus not be achieved by hydrosulphite bleaching alone even if the addition rate of hydrosulphite powder is increased the brightness gain is still 2 to 3 points short of the target and therefore brighter and more expensive kaolin has to be added to the pulp more specifically post bleaching with 0 2 0 3 na 2 s 2 o 4 could achieve a brightness gain of 0 9 points but further increasing the addition rate shows no positive effect on the brightness.