PRODUCING SODA PULP FROM ASPEN, 
57 
AUTOCLAVE TESTS ON ASPEN. 
A few autoclave tests on aspen (Populus tremuloides Michx.) were made in 1909. l 
The ordinary soda process was employed, but the digester used was a horizontal, rotary 
autoclave, made of 6-inch steel pipe, with a capacity of about 2 gallons. As the heat 
was furnished by Bunsen burners, there was no condensation or loss of liquid through 
overflow to modify the cooking conditions. Cooks were not blown, but the digester 
was quickly cooled to room temperature and then dumped. The pulps were thor- 
oughly washed with cold water and screened on a small diaphragm screen through 
slots of 0.006 inch width. The test material was cut from fairly young growth near 
Ridgeway, Colo. Portions of the logs tested, especially the centers and around knots, 
were discolored a dull reddish-brown, probably due to incipient fungous attack; other- 
wise the wood seemed to be sound. Chips were prej^ared in the manner described on 
page 15. Their sizes were five-eighths inch (with the grain) by three-sixteenths to 
one-fourth inch by one-half inch to 6 inches (both across the grain). 
The data resulting from the tests are shown in Table 15. The column headings 
have the same significance as those in Tables 10 to 14, except as otherwise indicated. 
However, in the bleaching tests the standard color matched was that of bleached 
sulphite pulp, and, as soda poplar pulp in commercial operations is never bleached 
to so white a color, the test data should be reduced somewhat in estimating the com- 
mercial value for bleach required. The values for loss on bleaching also are probably 
a little greater on this account. 
The tests fall naturally into two groups. One of these consists of cooks 1, 2, and 4, 
in which the concentration of caustic soda in the cooking liquors was varied. The 
other consists of cooks 3 and 5, in which the duration at maximum pressure was the 
chief variable. Increases either of concentration or of duration resulted in decreases 
in the yield of pulp, loss on bleaching, and bleach required, except possibly in the 
case of one cook. All of the pulps produced were thoroughly cooked. The yields, as 
compared with those secured in the more recent tests (see Table 11), were uniformly 
very low and the losses on bleaching very high. The difference may be due to the 
methods and apparatus used or to deterioration of the wood from fungous attack, or to 
both. If the wood had been perfectly sound, it does not seem probable that the lower 
yields would have been accompanied by the higher amounts of bleach required and 
the larger losses on bleaching, even though these effects were slightly augmented by 
the higher standard of bleaching. 
Table 15. — Cooking conditions and results of autoclave tests on aspen. 
Liquor charge. 
Initial 
volume of 
Chemicals charged per 
- 100 pounds of chips 
(bone-dry basis). 
Cook 
No 
Date of 
cook. 
Weight 
of chips 
charged 
(bone-dry 
Water 
in 
chips. 
Initial concentrations. 2 
Caus- 
digester 
liquors 2 
per 
pound of 
basis). . 
NaOH. 
Na 2 C0 3 . 
Total 
Na 2 0. 
ticity. 
chips 
(bone-dry 
basis). ' 
NaOH. 
Na 2 C0 3 . 
Total 
Na 2 0. 
Gravis 
Grams 
Grams 
1909. 
Lbs. 
P. ct. 
per liter. 
per liter. 
per liter. 
P.ct. 
Galls. 
Lbs. 
Lbs. 
Lbs. 
1 
May 25 
1.652 
33.5 
80 
7.4 
66.3 
93.5 
0.375 
25.0 
2.3 
20.7 
2 
May 27 
1.652 
33.5 
50 1.8 
39.8 
97.5 
.599 
25.0 
.9 
19.9 
3 
June 2 
1.652 
33.5 
90 
4.3 
72.3 
96.5 
.386 
29.0 
1.4 
23.3 
4 
June 8 
1.304 
18.3 
30 
1.4 
24.1 
96.5 
1.000 
25.0 
1.2 
20.1 
5 
July 3 
1.920 
15.0 
90 
4.3 
72.3 
96.5 
.390 
29.3 
1.4 
23.5 
i These tests were made by Mr. Edwin Sutermeister, formerly in charge of the pulp-testing laboratory 
of the Forest Service at Washington, D. C. 
2 The water in the chips when charged is not taken into consideration. 
