PRODUCING SODA PULP FROM ASPEN. 25 
conditions under which they were secured. It is evident that cooks 
which resulted in decreased yields produced easier bleaching pulps. 
For the higher values slight differences in yields are accompanied by 
marked differences in the ease of bleaching, but the effect rapidly 
diminishes until a large decrease in the yields affords little difference 
in the amounts of bleach required. This would be expected in view 
of the nature of the cooking reactions. The effect is first to remove 
the intercellular substances and part of the ligneous matters from the 
wood, then the cellulose itself begins to be attacked, and finally, after 
the greater part of ligneous matters has been removed, the cellulose 
alone is affected. The ease of bleaching is a measure of the amount 
of noncellulose matters present in the pulp. 
Other properties of the pulps when similarly platted against yields 
show more or less definite relationships, but are apt to be modified 
according to the cooking condition varied. For instance, when vary- 
ing the amount of caustic soda or the duration of cooking, decreased 
yields were attended by decreased strength of pulp; when initial con- 
centrations or pressures were varied, the strength increased as the 
yields decreased. Natural color, shives, and screenings, however, 
were little affected for yields below 54 per cent, no matter how pro- 
duced; for higher yields the color, shives, and screenings increased 
rapidly with increasing yields. The losses on bleaching followed 
fairly closely the amounts of bleach required, and hence decreased as 
the yields decreased. 
SIGNIFICANCE OP PROPERTIES. 
There are at present no accepted standards of quality or market 
grades of soda pulps. What may be sufficiently good quality for one 
purpose or one mill may be poor or medium quality for another. 
Aside from bulkiness and opacity, which depend mainly on condi- 
tions not studied in these experiments, the desirable properties of a 
pulp are, in general, as follows : 
(1) Low percentage of bleach required. 
(2) Low loss on bleaching. 
(3) High strength. 
(4) Durability (resistance to wear and decomposition). 
(5) Low ash content. 
(6) Few shives. 
(7) Absence of dirt. 
(8) Light color for the unbleached pulp. 
(9) Whiteness of the bleached pulp with freedom from certain undesirable tints. 
It is not often that any one pulp has the advantage over another in 
all of these properties, and for many uses some of them are of no 
importance. For aspen (poplar) or other short-fibered pulps used in 
the manufacture of book papers the properties which are given most 
