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 
slightly 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 quality 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 : 1 5 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. 
