20 



BULLETIN 



U. S. DEPARTMENT OP AGRICULTURE. 



from this wood in some of the tests is probably due to the presence 

 of cooking chemicals * which were not completely removed during the 

 washing treatments. Increasing amounts of ash as the cooking 

 conditions become more severe may be due to a difference in the 

 physical character of the cellulose produced under such conditions 

 and the resultant mcreased difficulty of leaching out and washing 

 away any residual and absorbed mineral matters. No tests were 

 2JD made to determine the char- 

 acter of the ash from any of the 



1.5 



a. 1.0 



0.5 





19 

































e' 



1^7 



^ 



^Sj 



1 4 







pulps. 



STRENGTH. 



.10 



.20 .30 .40 



POUNDS HaOH PER POUND OF WOOD 



2.0 



° 1.0 



1.0 



0.5 



1.0 













,0 . 







tf s 







13 













^K 



14 





• 

 12 









2 4 6 8 10 12 

 DURATION AT MAX. PRESSURE- HOURS 



0.5 



2? 



2I< 



'—is 



L-j^ 











18 



17 







60 



The strength of a pulp de- 

 pends chiefly upon three fac- 

 tors — (1) the strength of the 

 individual fibers ; (2) the felting 

 or matting quality of the fibers ; 

 and (3) the presence of gelatin- 

 ized fibers and other matters 

 which act as cementing ma- 

 terials. 



Severity of cooking is at- 

 tended by a weakening of the 

 cell walls and may result in a 

 decrease in the strength of the 

 pulp. This decrease of strength 

 was strongly marked in the tests 

 in which the more severe cook- 

 ing conditions were produced 

 by increasing the amount of 

 caustic soda. It was most rapid 

 up to the point where the fibers 

 were completely separated (indicated by the absence of shives), be- 

 yond which it was less pronounced. For increasing durations of 

 cooking the general trend 2 of the effect was the same as for 

 increasing amounts of chemical, but the total decrease in strength 

 was not quite so great in amount for the range of cooking conditions 

 investigated. 



70 80 90 100 110 120 

 MAX. PRESSURE PDS. PER SQ.IN. 



2?' 





25 





« 

















23 



ft- 1.0 



o.s 



40 50 60 70 80 90 100 110 

 CONCENTRATION NaOH -GRAMS PER LITER 



Fig. 7.— Effects of cooking conditions on the ash 

 content of pulp. 



1 Special precautions were taken, to eliminato the influence of dirt. Further it does not seem reason- 

 able that the cooking action which removed the lignin and other organic matters should have produced in 

 the fibrous residue or pulp a concentration of the mineral constituents which go to form the wood ash. 



2 The data are not sufficient for expressing the effect in detail. The true curve would be expected to 

 have a bend coinciding with the point of maximum yield of screened pulp or the point where the shives 

 are reduced to zero. 



