24 



BULLETIN" 80, U. S. DEPARTMENT OF AGRICULTURE. 



solved during bleaching or broken up into small particles, which are 

 removed in the washing operations. The partial removal of the min- 

 eral or ash-forming constituents from the pulp may also occasion some 

 loss. On the other hand, the ash in bleached pulp sometimes tends 

 to hicrease over that for the unbleached pulp (due to an accumulation 

 of lime compounds and other residues from the bleaching solution), 

 and hence may offset the loss due to other causes. 



RELATION BETWEEN PROPERTIES AND YIELDS. 



Many of the curves expressing the effects of the varying cookino- 

 conditions on the properties of the unbleached pulps have bends or 



30 































1 





TEST VARYING 



o AMOUNT OF CAUSTIC SODA 

 ODURATION OF COOKING 

 •PRESSURE OF COOKING 

 « CONCENTRATION OF CAUSTIC SODA 

 ©PRELIMINARY TEST 















































1 

















\ 





















































































o 

























































3?f 



^ • 





















a 



9 





09 















o 









a 



< 



) 

















































44 46 48 50 52 54 56 58 



YIELD-TOTAL CRUDE PULP -PER CENT 



Fig. 11. — Relation between yields and ease of bleaching. 



"breaks" at or near the values for the cooking conditions which 

 resulted in the highest yields of screened pulp. So general is this 

 that, with decreasing severity of cooking, the occurrence of sudden 

 changes of direction for curves expressing properties affords a reliable 

 indication that the yield of screened unbleached pulp is near its maxi- 

 mum. This is especially evident in the curves for ease of bleaching. 

 That properties of pulps are directly dependent upon yields is well 

 illustrated when amounts of bleach required are platted against yields 

 of total crude pulp, as in figure 11. Values for all of the cooks made 

 in these experiments have been platted, irrespective of the testing 



