12 



BULLETIN 343, U. S. DEPARTMENT OF AGRICULTURE. 



to ascertain the influence on the quality and quantity of pulp pro- 

 duced by the variation of the grinding variables, such as surface of 

 the stone, pressure on the cylinders, speed, temperature, etc. 



The cooking of wood prior to grinding is attended with a number of 

 changes in the physical characteristics of the wood which greatly 

 influence the quality of the pulp manufactured from it. The cooking 

 condition must be chosen according to the use to which the pulp is to 

 be put. For the manufacture of news-print paper from pitchy woods 

 it is essential that the treatment be a very mild one, and that the 

 duration of boiling or steaming and the temperature at which it is 

 carried on be such as to allow of the fiber being as light in color as 

 possible. Either the pressure, or corresponding temperature, must 

 be low and the cook of long duration, or the pressure higher and the 











































































260 















































































































































240 

































































S2 



HO 



JR 



; 

































































e 



401 



sm 





220 







































































































































3 



HO 



JR 



i 



200 



g teo 



« 160 



1 

 140 







































































































































4 



HO 



JR 



t 

































J 



*" 





































































S 



f 





<** 



> 



























































S 



S 



^ 



V 



































































^ 



































2 



HOI 



JKS 

























































^ _ 

























































































120 















































































































































100 































































































































































































































































































so 









































































" 10 20 90 40 50 60 70 80 

 STEAMING PRESSURE- POUNDS 



Fig. 4. — Effect of steaming pressure on color of pulp (average values of several runs on spruce). 



cook of much shorter duration. It is generally claimed that cooking 

 the wood under pressure while immersed in water will yield a lighter 

 pulp than steaming at the same pressure and for the same length of 

 time, but this result has not been noted. 



Boiling wood has certain disadvantages which are not found when 

 the steaming process is used. There is a considerable loss of heat, 

 and it is necessary to draw off condensed liquors to maintain the 

 temperature at any desired value. This makes it necessary to pay 

 greater attention to the process. If the temperature and duration 

 of the cook are the same, the steamed or boiled wood should be prac- 

 tically the same in color and other physical characteristics. One 

 decided advantage of steaming is the possibility of draining off the 

 condensed liquors in a concentrated form. This is of great benefit 

 when by-products are to be recovered. 



