22 



BULLETIN 



U. S. DEPARTMENT OF AGRICULTURE. 



bleach required was very rapid up to the point where shives were 

 eliminated; beyond this point the effect was less marked. It must 

 not be assumed, however, that the shives alone necessitated the larger 

 amounts of bleach. The presence of shives indicates an incomplete 

 cooking reaction and implies that considerable ligneous matter may 

 remain in the other (completely separated) fibers. 



The effect of severity of the 

 cooking conditions is especially 

 noticeable in the curves for the 

 tests varying the amount of 

 caustic soda and the duration 

 of cooking, since certain of the 

 pulps produced in these tests 

 were less thoroughly cooked 

 than any of those from the 

 other groups. 



30 



20 



10 



s 



.20 .30 .40 



POUNDS NaOH PER POUND OF WOOD 



30 



a: 20 



10 



Vis 



















V is 



«^»* 



13 



12 



















10 







LOSS ON BLEACHING. 



2 4 6 8 10 12 



DURATION AT MAX. PRESSURE-HOURS 



se 20 





[22 



21 



20 



















19 ' 



1 ' 







60 



70 80 90 100 110 120 

 MAX. PRESSURE-PDS. PER SO.. IN. 



to 



The curves showing the 

 losses on bleaching as affected 

 by the varying cooking condi- 

 tions are given in figure 10. 

 As would be expected, the loss 

 decreased with thoroughness 

 of cooking. In the tests vary- 

 ing the amounts of chemical 

 and the durations of cooking 

 the rate of decrease in bleach- 

 ing loss with greater severity 

 of cooking was fairly constant, 

 but it is probable that if the 

 cooking conditions were ex- 

 tended for higher values than 

 those used the curves would 

 approach parallelism "with the horizontal axis. Such an effect was 

 obtained for the tests in which the cooking pressures were varied. 

 It is not reasonable to believe that more severe cooking would result 

 in pulps which would suffer no loss whatever on bleaching. 



The platted points for the tests in which the initial concentrations 

 were varied are so few in number and so irregular in location that 

 they give little indication of the influence of this factor. However, 

 additional information is obtained from some earlier tests of the Forest 

 Service, summarized in Table 4. 



o 



40 





26 





















>-5 ' 





'ST" 



1 



23 



50 60 70 80 90 100 110 

 CONCENTRATION NaQH-GRAMS PER LITER 



Fig. 9. — Effects of cooking conditions on the ease of 

 bleaching. 



