PULP AND PAPER 



(a) 



(c) 



Fig. 1. Pulps. Lower left : Soft wood sulphite pulp, phase contrast, 300X. Upper left : Hard wood pulp 

 beaten in hollander to 57° S. R., phase contrast, 300X. Lower right: Cotton rags beaten in hollander to 

 50° S. R., phase contrast, 200X. Upper right: Straw pulp beaten in hollander to 38° S. R., phase con- 

 trast, 350 X. 



When pulping is less thorough it is usually 

 possible to identify the constituent fibers. 

 In the case of rag fibers pulping causes in 

 the first place internal fibrillation often at- 

 tended by cross fracture. Despite this frac- 

 ture, however, the typical fiber characteris- 

 tics, such as the X-shaped displacements in 

 the case of flax, usually remain fairly \'isible. 

 This internal fibrillation is followed by exter- 

 nal fibrillation, whereby a network of fine 



fibrils ari.ses. Cell wall membranes are not 

 found. 



In the case of hard wood fiber, too, pulp- 

 ing causes considerable fibrillation. In the 

 first instance, similarly to rags, this is inter- 

 nal. Besides this there is greater damage 

 which loosens membranes, both from the 

 fibei's and the vessels, which lie as two-di- 

 mensional fibrils in the fiber suspension. 

 These membranes ai"e clearly visible only 



399 



