14 BULLETIN 343, U. S. DEPARTMENT OF AGRICULTURE. 
rapidly with increased pressure due to the dissolving action of the 
water and the transformation of portions of the wood into water 
soluble material which is washed out in the grinding process. 
Variation of the period of cook also has a marked influence upon the 
horsepower consumption per ton of pulp. When wood is ground 
under the same conditions of grinder pressure, speed, temperature, etc., 
it is found that after a period of four to six hours of cooking the 
maximum value of power consumption is obtained. For a greater 
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25 
[POINTS PER POUND) 
STRENGTH FACTOR 
rt) 
°o 
HOURS oF STEAMING 
Fic. 6.—Effect of duration of steaming upon the strength of the pulp. (Spruce runs 199-209, inclusive.) 
«405 
or lesser length of time of cooking the horsepower consumption per 
ton decreases (fig. 8). 
OTHER FACTORS. i 
The variation of the yield of pulp from 100 cubic feet of solid wood 
with the duration of cook and temperature of cooking has been pointed 
out. It would seem that most of the loss would occur in the cooking” 
process itself, but determinations of the amount of bone-dry wood 
charged to the cooker and the amount of bone-dry material taken 
from it after steaming shows that the loss in cooking as volatile 
materials and water-soluble substances which leach out when the 
wood is in the 2-foot lengths is remarkably low, being from 5 to 8 per | 
cent. It appears that the great loss which takes place in the produc- 
