30 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



effects. 1 While various gradations resulted, 2 the experimental pulps 

 may be classified in the following three groups: 



Overcooked pulps. — Severe digestion treatments resulted in "over- 

 cooked" pulps, examples of which are seen in Plates II and III. 

 The walls of the fibers show a considerable degree of weakness, 

 as indicated by their thin transparent appearance and by tbeir 

 much twisted and fractured condition. The relative number of 

 vessels present in the pulp is low as compared with the normal 

 number present in the wood, and the pits and other markings on 

 them are only dimly visible. Many of the vessels remaining are 



COOK MO. 



| J 



» i 



6 5 4 



A 

















B 



1 



^ 



^ 

















f i 



r — 



C 





N 



<v 











D 



















' 1 



^« — i 













E 

















1 — i 



A 



i 1 



*— — 1 



1 1 



1 1 



» ^ 







B ' 















1 



C ' 



s 



1 — 1 



1 H 



> 1 



>— 1 



1— — 



I 



— i 

 



1 J 



*— — 1 



1 1 



1 1 



» « 



I 





E 

















jO 4 20 .30 .40 

 * POUNDS NaOH PER POUND OF WOOD 



60 70 80 90 100 110 120 

 MAX. PRESSURE- PDS. PER SO. IN. 



A 





























B 





























C 



















D 































1 



>— 



E 



— ( 



> 



1 



> 1 











2 4 6 8 10 12 



DURATION AT MAX. PRESSURE- HOURS 



40 50 SO 70 80 90 100 110 

 CONCENTRATION NaOH- GRAMS PER LITER 



Fig. 15.— Effects of cooking conditions on pulp fibers. A, abundance of wood vessels; B, ray cells; 

 C, fiber bundles, or shives; D, prominence of vessel markings; and E, apparent strength of fiber 

 walls. 



ragged and partly disintegrated; and the pulp, for the most part, 

 is also characterized by an absence of the comparatively thin-walled, 

 delicate ray cells. Fiber bundles abo are absent, since these are 

 made up of fibers bound together by groups of the brick-shaped ray 

 or parenchyma cell. The indistinctness of the vessels and fibers is 

 due chiefly to the removal of the ligneous infiltrations of the cell 

 walls, in consequence of which the elements developed very little 

 color from the particular stain used in making the microscopic 

 mounts. 



Well-cooked pulps. — Pulps produced under less severe conditions 

 are made up of stronger fibers, such as shown in Plates IV and V. 



1 The remarks following the title of each plate and the discussion in the text are not based on the fields 

 shown in the photomicrographs alone. 



2 The photomicrographs, in the order of their sequence, show gradations of severity of cooking. 



