16 
BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 
YIELDS. 
The effects on yields of pulp and screenings are expressed by the 
curves in figure 4, in which the yields are plotted against the amount 
of caustic soda, the duration of cooking, the pressure of cooking, and 
the initial concentration of caustic soda. 
AMOUNT OF CAUSTIC SODA. 
With increases in the amount of caustic soda per pound of woo 1 
the yield of total crude pulp decreased at the rate of about 1 per 
cent for each 2 per cent of caustic (0.02 pound NaOH per pound of 
so 
Ss 
9 r 
^n 
/ 
7 
S 
40 
/ 
4 
60 
i 
bn. . 
50 
b 
L 
f 
to 
i 
ji 
.10 .20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 
2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 
■ 
3 20 
111 
r 
* 
\ 
K 
i 
9 
\ 
s 
s 

\ 
1 
« 
5 
4 
s 
15 
4 
t 
J 
? 
! 
8 
.10 .20 .30 .40 
POUND NaOH PER POlWffl OF WOOD 
2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 
3 60 
Ul 
~2Z 
20 
>- 
5 50 
2'.' 
a 
17" 
3 60 
50 
40 
26* 
25 
23* 
60 70 80 SO 100 110 120 
MAX. PRESSURE-PDS. PER SO. IN. 
O -TOTAL CRUOS PULP 
40 50 60 70 80 90 100 110 
CONCENTRATION NaOH-GRAMS PER LITER 
Fig. 4.— Effects of cooking conditions on yields of total crude pulp, screened unbleached pulp, and 
screenings. 
wood). The yield at zero caustic soda would probably fall between 
80 and 90 per cent, being influenced only by the cooking effect 1 of 
the water condensed from the steam used in cooking. For high 
amounts of caustic soda the curve tends to approach parallelism 
with the horizontal axis. The yield would not be expected to become 
zero unless exceedingly large amounts of caustic were used. 2 
For amounts of caustic soda above what may be considered the 
minimum for successful cooking under the conditions used, the yield 
i See Tauss's experiments, Table 1. 
2 Tauss used for a single boiling as high as 7 pounds of caustic soda per pound of wood, and the yield 
or imdissolved material after three hours at 58.8 pounds per square inch steam pressure amounted to 8.52 
per cent for beech and 2.87 per cent for pine. With 4 pounds caustic soda per pound of wood in each of 
three successive three-hour treatments under a steam pressure of 132.3 pounds per square inch, the yields 
for the two woods were 20.61 per cent and 18.20 per cent, respectively. This latter proportion of caustic 
soda was ten or more times as great as is ordinarily employed in commercial practice. Also the other 
cooking conditions were proportionately more severe. 
