PRODUCING SODA PULP FROM ASPEN. 



27 



40 



30 



20 





.10 



.20 .30 40 

 POUNDS NaOH PER POUND OF WOOD 



30 



u. 20 





IS 



14 



•' 3 



,« 



•" 















— •« 

















2 4 6 8 10 12 

 DURATION AT MAX. PRESSURE-HOURS 



With increasing durations of cooking the efficiency in the use of 

 caustic soda increased until it reached a constant maximum value. 

 An efficiency of 95 per cent was obtained by seven hours' cooking at 

 maximum pressure, and, since no greater efficiency was secured by 

 continuing the cooking four additional hours, it is apparent that this 

 represents the maximum efficiency attainable. That the cooking 

 reactions are not due entirely to the presence of active caustic soda 

 is indicated by the fact that after the 95 per cent efficiency had been 

 attained increased durations resulted in some further cooking effect 1 

 (see curves for yields and prop- 

 erties of pulps) with no increase 

 in the amount of chemical con- 

 sumed. Increasing the pres- 

 sure also resulted in greater 

 efficiency in the use of caustic 

 soda until a maximum of 95 

 per cent was obtained. 



In all groups of tests in which 

 a constant amount of caustic 

 soda was charged into the di- 

 gester for each cook, greater 

 percentage efficiency in its use 

 could mean only a greater 

 actual consumption of the 

 chemical. In the group of 

 tests varying the amounts of 

 caustic soda, the decrease in 

 percentage efficiency was ac- 

 companied also by increase in 

 the actual consumption. It is 

 thus apparent that the more 

 thorough cooking, whether 

 produced by increasing the 

 amount of chemical in the 

 charge or the duration or the 

 pressure of cooking, is, in large part at least, due to the greater com- 

 pleteness of the reaction between the chemical and the wood. 



The tests employing various initial concentrations of caustic soda 

 in the digester liquors (the amount of caustic soda charged remaining 

 the same) seemingly do not bear out this conclusion. In most 

 respects the determinations of yields and properties of the pulps in 

 these tests indicated that the more concentrated solutions resulted 

 in more thorough cooking, but no increase in the consumption of 

 chemical occurred; in fact, with increase of concentration, a decrease 



60 



70 80 90 UO 110 120 

 MAX. PRESSURE-POS. PER SOUIN. 



50 60 70 80 

 CONCENTRATION NaOH- 



90 100 HO 

 GRAMS PER LITER 



Fig. 13.- 



-Effects of cooking conditions on the amount 

 of caustic soda consumed. 



1 For the effect of water alone, see Tauss's experiments, Table 1. 



