14 



BULLETIN 343, U. S. DEPARTMENT OF AGRICULTTJBE. 



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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HOURS OF STEAMINS 



Fig. 6.— Effect of duration of steaming upon the strength of the pulp. (Spruce runs 199-209, inclusive.) 



or lesser length of time of cooking the horsepower consumption per 

 ton decreases (fig. 8). 



OTHER FACTORS. 



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- 



