SUITABILITY OF LONGLEAF PINE FOR PAPER PULP. 



21 



was determined by actual test. The digester pressures, therefore, 

 correspond to the temperatures of saturated steam; and values of 

 each may be converted into the other by means of standard steam 

 tables. 



Table 8 shows the effect on yield of variations of pressure from 40 

 to 140 pounds per square inch. As the pressures increased, the 

 yields decreased. Cook 45, with a pressure of 40 pounds per square 

 inch, resulted in a product so much undercooked that no pulp could 

 be prepared from it. The yield, of course, was very high. Cook 46, 

 using a pressure of 140 pounds per square inch, resulted in 50 per 

 cent yield. For intermediate pressures the yields were correspond- 

 ingly higher. 



TABLE 8. Effect of varying pressures on the yield of pulp. 



Weight of chips charged (bone-dry basis) pounds. . . 1. 000 to 1. 005 



Water in chips, per cent. . 10. 4 to 11. 



Causticity ofliquorcharge do 53.5 



Sulphidity of liquor charge do 27. 4 



Initial volume of digester liquors per pound of chips (bone-dry basis) gallons. . . 0. 667 to 0. 680 



Duration of cooking, total . . hours. . 3. 



Duration of cooking at zero gauge pressure do 0. 1 



Duration of cooking at maximum gauge pressure do 2.0 to 2.3 



Total duration of beater treatment (at light brush only) do or 1 



1 The same values apply to the 



(P. L. 138, S. L. 3 6.) 

 2 Wood not cooked; no pulp prepared. 



Pulps produced with the higher pressures were stronger and had 

 better wearing properties than those resulting from the lower pres- 

 sures. With lower pressures the pulps became more and more 

 brittle and gradually lost their soft, pliable, leather-like feel. The 

 pulps resulting from the lower pressures were the more brown in 

 color. 



The best pressure conditions for these tests seemed to be from 100 

 to 140 pounds per square, inch. If larger amounts of chemicals had 

 been employed, pulps of the same yield and properties would prob- 

 ably have resulted from pressures of 80 to 100 pounds per square 

 inch. 



