PRODUCING SODA PULP FROM ASPEN. 
27 
40 
30 
20 
.10 
.20 .30 40 
POUNDS NaOH PER POUND OF WOOD 
30 
u. 20 
is „-W-- — ® — ~~ * ®~ 
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 
70 80 90 100 110 120 
MAX. PRESSURE-PDS. PER SO. IN. 
50 60 70 80 90 100 110 
CONCENTRATION KaOH- 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. 
