22 
BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. 
EFFECTS OF VARYING THE DURATIONS OF COOKING. 
Since the time from the start of a cook until maximum pressure was 
obtained in the autoclave was practically constant (varying from 
0.5 to 0.7 hour), only the total duration of cooking will be considered* 
Table 9 shows how the yields were affected for total durations varying 
from one to nine hours in three series of tests, using high, medium, 
and low amounts of chemicals. In the case of the first series, em- 
ploying very high amounts of chemicals, 55.9 per cent of the wood 
(giving a yield of 44.1 per cent) was dissolved during two hours of 
cooking, while by cooking for seven hours longer an additional loss 
of only 12.8 per cent occurred. Cook 124, with a total duration of 
but one hour, afforded the best pulp and the highest yield for this 
series. This pulp came from the autoclave in the form of soft chips, 
and the resultant paper made from the beaten pulp was firm and 
strong, with good resistance to wear. The other pulps were soft 
and fuzzy, due to overcooking. As the duration increased, the 
color of the pulps changed from brown (cook 124) to light gray 
(cook 78). 
Table 9. — Effect of varying durations of cooking on the yield of pulp. 
Weight of chips charged (bone-dry basis), pounds. . 0. 964 to 1. 034 
Water in chips per cent . . 16. to 24. 4 
Causticity of liquor charge do 51.6 to 53. 3 
Sulphidity of liquor charge do 26. 5 to 27. 4 
Initial volume of digester liquors per pound of chips (bone-dry basis) gallons. . 0. 667 to 0. 680 
Duration of cooking at zero gauge pressure hours. . 0. 1 
Maximum gauge pressure per square inch pounds. . 90 
Total duration of beater treatment (at light brush only) hours.. 1.5 or 2 
FIRST SERIES. 
Cook 
No. 
Liquor charge, initial concen- 
trations. 
NaOH. 
NasS. 
All 
sodium 
com- 
pounds 
as Na 2 0. 
Chemicals charged per 100 
pounds of chips (bone-dry 
basis). 
NaOH. 
Xa 2 5. 1 
AU 
sodium 
com- 
pounds 
as Na«0. 
Duration of cooking. 
Total. 
I Yield of 
crude 
pulp 
At maxi- (bone-dry 
mum I basis), 
gauge 
pressure. 
124 
125 
80 
78 
Grams 
per liter. 
71.9 
71.9 
72.0 
72.0 
Grams 
per liter. 
36.0 
36.0 
36.0 
36.0 
Grams 
per liter. 
104.7 
104.7 
104.7 
10S.1 
Pounds. 
40.0 
40.0 
40.0 
40.0 
Pounds. 
20.0 
20.0 
20.0 
20.0 
Pounds. 
5S.3 
58.3 
58.2 
60.1 
Hours. 
1.0 
2.0 
5.0 
9.0 
Hours. 
0.5 
1.5 
4.3 
8.3 
Per cent. 
57.4 
44.1 
37.8 
31.3 
SECOND SERIE 
s. 
123 
44.9 
22.5 
65.4 
25.0 12.5 
36.4 
1.0 
0.5 
68.6 
126 
44.9 
22.5 
65.4 
25.0 12.5 
36.4 
2.0 
1.5 
48. 5 
84 
45.0 
22.7 
65.6 
25.0 12.6 
36.5 
5.0 
4.3 
45.0 
S3 
45.0 
22.7 
65.6 
25.0 12.6 
36.5 
9.0 
8.3 
3^.2 
THIRD SERIES 
86 
21.6 
10.8 
31.4 
12.0 
6.0 
17.4 
1.0 
0.3 
SO. 9 
127 
21.6 
10.8 
31.6 
12.0 
6.0 
17.6 
2.0 
1.5 
66-7 
88 
21.2 
10.6 
30.8 
12.0 
6.0 
17.4 
5.0 
4.3 
59.0 
S7 
21.6 
10.8 
31.4 
12.0 
6.0 
17.4 
9.0 
S.3 
57.0 
The same values apply to the NajS0 4 used. 
(P. L.— 138, S. L.— 176.) 
