SUITABILITY OF LONGLEAF PINE FOR PAPER PULP. 23 



In the second series, when medium amounts of chemicals were 

 used, prolonging the durations of cooking likewise resulted in 

 decreasing the yields. The yield for cook 123, with a total duration 

 of one hour, was 68.6 per cent; and cook 83, with a total duration of 

 9 hours, had a yield of 38.2 per cent. With a 2-hours' duration the 

 amount of the wood dissolved was 51.5 per cent (48.5 per cent yield), 

 while with a 7-hours' longer cooking period the loss was only 10.3 per 

 cent additional. The best kraft pulps were obtained from cooks 126 

 and 84, with total durations of 2 and 5 hours, respectively. The 

 resultant papers were firm and strong, and resistant to wear. Cook 

 123, using a duration of 1 hour, resulted in a weak, brittle, and under- 

 cooked pulp, while the pulp from cook 83, which had a duration of 9 

 hours, was soft, fluffy, and evidently overcooked. 



The same general effects resulted from varying the durations in the 

 third series of tests in which comparatively low amounts of chemicals 

 were employed. In this case, however, the best pulps were produced 

 with the longer durations, 5 hours for cook 88 and 9 hours for cook 87. 

 The tests employing shorter durations resulted in weak and 

 brittle pulps, due to undercooking. The pulp from cook 88 was 

 shghtly inferior to that from cook 87, but both would be considered 

 of fair quality for making kraft wrapping paper. 



The results from the three series of tests indicate that cooks 

 employing high amounts of chemicals and very short durations will 

 afford pulps of a quahty and yield similar to those obtained when 

 using medium amounts of chemicals and medium durations and to 

 those resulting from the use of low amounts of chemicals and com- 

 paratively long durations. It is evident, however, that much more 

 careful control of the operations must be exercised in order to obtain 

 consistent results when high amounts of chemicals are employed. 



EFFECTS OF VARYING THE INITIAL CONCENTRATIONS. 



In each of two series of tests varying the initial concentrations of 

 chemicals in the liquor charge the amounts of chemicals per 100 

 pounds of wood were held constant as follows: 15 pounds of caustic 

 soda, 7.5 pounds of sodium sulphide, and 7.5 pounds of sodium 

 sulphate for the first series, and 12 pounds of caustic soda, 6 pounds 

 of sodium sulphide, and 6 pounds of sodium sulphate, for the second 

 series. Since the amounts of chemicals were held constant, and the 

 concentrations varied, the initial volumes of digestor liquors per pound 

 of chips also varied accordingly. Table 10 shows the effect of the 

 varying concentrations on the yield of pulp. 



