20 
BULLETIN -80, U. S. DEPARTMENT OF AGRICULTURE. 
from this wood in some of the tests is probably due to the presence 
of cooking chemicals 1 which were not completely removed during the 
washing treatments. Increasing amounts of ash as the cooking 
conditions become more severe may be due to a difference in the 
physical character of the cellulose produced under such conditions 
and the resultant increased difficulty of leaching out and washing 
away any residual and absorbed mineral matters. No tests were 
made to determine the char- 
acter of the ash from any of the 
25 
Q. 1.0 
0=5 
■ 
\ 
S, 
^* ? 
6, 
_5/ 
fc "*4 
pulps. 
STRENGTH. 
. 1 
.20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 
2,0 
1.0 
1.0 
0,5 
^_ _J^^ 
2 4 6 8 10 12 
DURATION AT MAX. PRESSURE- HOURS 
70 80 30 100 110 120 
MAX. PRESSURE PDS. PER SO. IN. 
The strength of a pulp de- 
pends chiefly upon three fac- 
tors — (1) the strength of the 
individual fibers; (2) the felting 
or matting quality of the fibers ; 
and (3) the presence of gelatin- 
ized fibers and other matters 
which act as cementing ma- 
terials. 
Severity of cooking is at- 
tended by a weakening of the 
cell walls and may result in a 
decrease in the strength of the 
pulp . This decrease of strength 
was strongly marked in the tests 
in which the more severe cook- 
ing conditions were produced 
by increasing the amount of 
caustic soda. It was most rapid 
up to the point where the fibers 
were completely separated (indicated by the absence of shives), be- 
yond which it was less pronounced. For increasing durations of 
cooking the general trend 2 of the effect was the same as for 
increasing amounts of chemical; but the total decrease in strength 
was not quite so great in amount for the range of cooking conditions 
investigated. 
1 Special precautions were taken to eliminate the influence of dirt. Further it does not seem reason- 
able that the cooking action which removed the lignin and other organic matters should have produced in 
the fibrous residue or pulp a concentration of the mineral constituents which go to form the wood ash. 
2 The data are not sufficient for expressing the effect in detail. The true curve would be expected to 
have a bend coinciding with the point of maximum yield of screened pulp or the point where the shives 
are reduced to zero. 
o- 1.0 
0.5 
^^-—. 3, a. s< 
40 50 60 70 80 90 100 110 
CONCENTRATION NaOH -GRAMS PER LITER 
Fig. 7.— Effects of cooking conditions on the ash 
content of pulp. 
