26 



BULLETIN 80, IT. S. DEPARTMENT OF AGRICULTURE. 



consideration are freedom from dirt and strives and low percentage of 

 bleach required, with the attendant low loss on bleaching. Both 

 undercooked and overcooked pulps are to be avoided. 



CONSUMPTION OF CAUSTIC SODA. 



By consumption of caustic soda is meant the neutralization of the 

 free or active caustic soda (NaOH) existing as such in the digesting 



liquors. The neutralization re- 



WOr^: 



90 



80 



70 



K)0 



90 



80 



70 



100 



90 



80 



? 



















1 



1 ^ 



1 



16 

























.20 .30 .40 



POUNDS NaOH PER POUND OF WOOD 









^£- 



k 



% 









/i 5 



' *I4 













Y 

















2 4 6 8 10 12 

 DURATION AT MAX. PRESSURE-HOURS 



suits from the combination of 

 the sodium (Na) of the alkali 

 with the acid products derived 

 from, the hydrolysis of the 

 lignified fibers during cooking. 1 

 The black liquors at the end 

 of the cooking treatments con- 

 tain in dissolved form these 

 nonalkaline, sodium com- 

 pounds, together with the re- 

 maining free caustic soda. 



The effects of varying the 

 cooking conditions on the con- 

 sumption of caustic soda, ex- 

 pressed in per cent of the 

 amount charged or the effi- 

 ciency in its use, are shown in 

 figure 12. The actual con- 

 sumption in pounds per 100 

 pounds of wood is shown in 

 figure 13. 



As would naturally be ex- 

 pected, the greatest compara- 

 tive efficiency for the cooks 

 made with varying quantities 

 of caustic soda resulted from 

 the use of the smaller amounts. 

 However, when very small 

 amounts were employed, the 

 cooking reactions were not sufficiently complete, 2 as indicated by the 

 curves for yields and properties of the pulps. In this group of tests 

 well-cooked pulps were first obtained with about 0.2 pound of NaOH 

 per pound of wood. The efficiency in the use of the caustic at this 

 point was about 85 per cent. 



i See De Cew's discussion, p. 0. 



2 It is a well-known chemical law that in order to carry a reaction to a given degreeof completion for one 

 of the reacting substances it is necessary to have available a certain excess of the other chemical or chemicals 

 which take part in the reaction. This means that the efficiency in the use of the chemical can not be 100 

 per cent. The speed of the reaction is proportional to the amount of the excess. 



^ 70 











( 



!3-— i 



17 











/^l 



>» 









< 



Pa 



,21 



'20 











60 



70 80 90 100 110 120 

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



100 



90 



80 





28 



















« 



sr— 





24 



1 



23 



■— — - 



40 



SO 60 70 80 90 100 110 

 CONCENTRATION NaOH -GRAMS PER LITER 



Fig 



12. — Effects of cooking conditions or 

 ciency in the use of caustic soda. 



the efli- 



