24 
BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 
solved during bleaching or broken up into small particles, which are 
removed in the washing operations. The partial removal of the min- 
eral or ash-forming constituents from the pulp may also occasion some 
loss. On the other hand, the ash in bleached pulp sometimes tends 
to increase over that for the unbleached pulp (due to an accumulation 
of lime compounds and other residues from the bleaching solution), 
and hence may offset the loss due to other causes. 
RELATION BETWEEN PROPERTIES AND YIELDS. 
Many of the curves expressing the effects of the varying cooking 
conditions on the properties of the unbleached pulps have bends or 
30 
20 
f 
TEST VARYING 
o AMOUNT OF CAUSTIC SODA 
ODURATION OF COOKING 
•PRESSURE OF COOKING 
^CONCENTRATION OF CAUSTIC SODA 
©PRELIMINARY TEST 
] 
| 
/ 
/ 
o 
1/ 
JLx 
^ m 

9 
9 

• 
< 
> 
! 18 
o 
UJ 
ce 
I 16 
UJ 
i » 
UJ 
a ft 
10 
6 
6 
44 46 48 50 52 54 56 58 
YIELD-TOTAL CRUDE PULP -PER CENT 
Fig. 11.— Relation between yields and ease of bleaching. 
" breaks" at or near the values for the cooking conditions which 
resulted in the highest yields of screened pulp. So general is this 
that, with decreasing severity of cooking, the occurrence of sudden 
changes of direction for curves expressing properties affords a reliable 
indication that the yield of screened unbleached pulp is near its maxi- 
mum. This is especially evident in the curves for ease of bleaching. 
That properties of pulps are directly dependent upon yields is well 
illustrated when amounts of bleach required are platted against yields 
of total crude pulp, as in figure 11. Values for all of the cooks made 
in these experiments have been platted, irrespective of the testing 
