26 
BULLETIN 
TJ. 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. 
100 
20 
SO 
70 
.20 .30 ,40 
POUNDS NaOH PER POUND OF WOOD 
too 
so 
80 
70 
*^~ 
B 
% 
4 
' # 14 
Y 
ui 
100 
2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 
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- 
sults from the combination of 
the sodium (Na) of the alkali 
with the acid products derived 
from the hydrolysis of the 
lignined 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. 
1 See De Cew's discussion, p. 6. 
2 It is a well-known chemical law that in order to carry a reaction to a given degree of 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. 
90 
80 
™ 70 
I 
»!1— A— 
1 17 
L ! ' 
1 
^ A 
> 2 > 
'20 
60 
70 80 90 100 IX) 120 
MAX. PRESSURE- PD3. PER Sa. IN. 
^j 
50 
80 
2S 
- -. 
( 
ST-- 
24 
1 
2L. 
40 
50 SO 70 8C 
CONCENTRATION NaOH- 
90 100 HO 
GRAMS PER LITER 
Fig. 12.— Effects of cooking conditions on the effi- 
ciency in the use of caustic soda. 
