18 
BULLETIN 1298, U. S. DEPARTMENT OF AGRICULTURE 
Table 4. — Soda cooks of sound and decayed woods 
[Yield percentages are based on oven-dry weights of wood and pulp] 
Sam- 
ple 
No. 
Cook 
No. 
Pulp 
No. 
Description 
Maxi- 
mum 
steam 
pres- 
sure 
Time 
at 
maxi- 
mum 
pres- 
sure 
Total 
time 
of 
cook 
NaOH 
per 100 
pounds 
oven- 
dry 
chips 
Liquor 
per 100 
pounds 
oven- 
dry 
chips 
Alkali 
con- 
sumed 
Yield 
of 
crude 
pulp 
Yield 
of 
screen- 
ings 
Yield of 
screened 
pulp 
~~256(T 
2541 
2542 
2552 
109 
6 
7 
228 
3 
4 
540 
2559 
2557 
40 
542D 
552D 
Sound spruce- - 
Decayed 
spruce. 
do 
Sound hem- 
lock. 
Decayed hem- 
lock. 
Decayed as- 
pen. 
Lbs. 
100 
100 
100 
105 
100 
102 
Hrs. 
i 
5 
5 
I 
5 
4| 
Hrs. 
2\ 
6 
6 
4f 
6 
Pounds 
20.3 
20.5 
20.5 
20.5 
20.5 
26.2 
Gallons 
27 .4 
31.6 
31.7 
27.2 
31.4 
30.3 
P.ct. 
75.9 
89.9 
95.9 
82.0 
95.3 
P.ct. 
50.2 
42.6 
48.8 
46.0 
45.5 
44.0 
P. ct. 
1.4 
16.8 
0.1 
4.9 
P. ct. 
48.8 
42.6 
32.0 
45.9 
45.5 
39.1 
In the soda process the yields of spruce pulps showed a wider range 
than those for sulphite, with the rejected spruce wood again giving an 
abnormally low yield. The aspen wood, No. 2552 (pulp No. 552 D), 
yielded only 39.1 per cent, notwithstanding the use of an exceptionally 
large proportion of chemical. Badly decayed wood is soluble to a high 
degree in caustic soda solution, so much so that during the early stages 
of cooking the concentration of the active alkali is reduced to such an 
extent that the pulping process can not be completed. The result is a 
large percentage of screenings and a low yield of screened pulp. For 
example, the badly decayed spruce wood, No. 2541, was soluble in 
caustic soda (see Table 7) to the extent of 62.3 per cent. It was 
found by repeated trials that the 20.5 pounds of alkali sufficient to 
pulp 100 pounds of sound wood was insufficient for this decayed 
spruce, the yield from which (pulp No. 2557) consisted of 16.8 per cent 
of screenings and only 32.0 per cent of screened pulp. 
Attention should be directed to the fact that these yields are ex- 
pressed on an oven-dry weight basis both for the wood and the pulp. 
If it had been possible to convert the yields to a pounds-per-cord basis, a 
distinct lowering of yield with increasing decay would doubtless have been 
evident even in the less extreme cases. Such a conversion involves two 
factors : The density of the wood, and the solid wood volume per cord. 
Both factors, even for sound wood, show wide variation, so that any 
figures given for the yield per cord would be practically meaningless. 
If solid volume, rather than the number of cords, be taken as the 
basis, then density becomes the chief factor to be considered ; and of 
two woods of different densities but yielding equal weights of pulp, 
that with the lower density will, obviously, show the lower yield per 
unit volume. 
Comparisons on that basis would be fairly exact but for the fact 
that data on the density of the woods used for the pulping tests are 
insufficient, and in some cases apparently conflicting; nevertheless 
they indicate, in general, that the progress of decay is accompanied by 
a decrease in density. This is certainly true in the advancecl stages of 
decay, and the decrease in average density is doubtless roughly pro- 
portional to the increase in decay. Further investigation of this 
point would be very desirable because of its direct and vital bearing 
upon mill operation. 
