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 OF 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 



