8 
BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. 
treatments are necessary than if the pulps are to be used in natural- 
color wrapping papers. The present experiments apply more espe- 
cially to the latter, for which the important properties are strength, 
toughness, and resistance to wear. The terms mild, medium, and 
severe cooking, and undercooked, well-cooked, and overcooked pulps 
used in the following discussion are significant only with respect to 
the object of the tests. 
MILD COOKING TREATMENTS. 
The less severe the cooking of a wood the larger will be the yield 
of crude pulp. However, there is a point at which the pulp will begin 
to lose its valuable properties for making wrapping papers. For cook 
71 the digesting conditions were outlined to give a much undercooked 
pulp (see Table 1), but the treatment given the wood was even less 
severe than is indicated by the recorded data, since a portion of the 
digester liquor was lost through leakage soon after the cook had been 
started. The crude unbeaten pulp from this cook was full of soft 
chips, which, while hard enough to resist the action of a stream of 
water under pressure, could easily be picked apart with the fingers. 
The paper made from the beaten pulp had a strength factor of 0.50, 
was moderately tough, and had fair wearing properties. As a wrap- 
ping paper it would be considered of medium grade. The yield, 61.2 
per cent, or 2,172 pounds per solid cord, was very high, considering 
the quality of pulp obtained. Pulps produced under less severe 
cooking conditions had higher yields (see autoclave tests, pp. 14-24), 
but the quality was not so good, as evidenced by brittleness, lack of 
strength, and poor wearing properties. 
Table 1. — Record of semicommercial tests using the sulphate process. 
Li quo 
r charge. 
Initial 
volume 
of di- 
Weight 
Initial concentrations. 
gester 
otchips 
charged 
Water 
liquors 
Cook 
per 
No. 
(hone- 
dry 
chips. 
SO> 
All 
Caus- 
Sul- 
phid- 
ity. 
pound 
of 
basis.) 
NaOH. 
Na 2 C0 3 . 
Na 2 S. 
com- 
pounds 
Na 2 S0 4 . 
sodium 
com- 
ticity. 
chips 
(bone- 
as 
pounds 
dry 
Na 2 S0 3 . 
as Na 2 0. 
basis). 
Grams 
Grams 
Grams 
Grams 
Grams 
Grams 
Pounds. 
Per ct. 
per liter. 
per liter. 
per liter. 
per liter. 
per liter 
per liter. 
Per ct. 
Per ct. 
Gallons. 
171 
38.62 
34.6 
26.5 
1.4 
13.2 
1.8 
13.2 
38.5 
53.3 
27. 3 
0.679 
77 
38.61 
34.7 
44.6 
2.7 
22.3 
2.9 
22.1 
64.9 
53.2 
27.3 
.538 
81 
23.97 
22.7 
60.4 
3.2 
30.0 
4.0 
30.0 
87.6 
53.4 
27.2 
.300 
85 
23.97 
22.7 
36.0 
1.9 
18.0 
2.4 
18.0 
52.3 
53.3 
27.3 
.500 
92 
23. 97 
22.6 
48.0 
2.4 
30.0 
4.0 
30.0 
77.5 
48.0 
30.8 
.300 
98 
23.97 
22.6 
28.8 
1.4 
14.4 
1.9 
14.4 
41.8 
53.3 
27.4 
.500 
113 
25.38 
18.2 
34.2 
1.9 
17.1 
2.2 
18.5 
50.4 
52.6 
27.0 
.700 
138 
25.38 
18.2 
59.9 
3.0 
30.0 
3.9 
30.0 
87.0 
53.4 
27.4 
.400 
141 
25.38 
18.2 
60.0 
3.3 
15.0 
2.1 
30.0 
74.4 
62.4 
16.0 
.400 
146 
25.38 
18.2 
26.5 
1.4 
13.2 
1.8 
13.2 
38.5 
53.3 
27.3 
.680 
147 
26.67 
12.5 
26.5 
1.2 
13.2 
1.8 
13.2 
38.4 
53.4 
27.4 
.680 
148 
26.67 
12.5 
26.5 
1.2 
13.2 
1.8 
13.2 
38.4 
53.4 
27.4 
.680 
A portion of the digester liquor was lost, due to leaks during the early stages of cooking. 
