16 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



YIELDS. 



The effects on yields of pulp and screenings are expressed by the 

 curves in figure 4, in which the yields are plotted against the amount 

 of caustic soda, the duration of cooking, the pressure of cooking, and 

 the initial concentration of caustic soda. 



AMOUNT OF CAUSTIC SODA. 



With increases hi the amount of caustic soda per pound of wood 

 the yield of total crude pulp decreased at the rate of about 1 per 

 cent for each 2 per cent of caustic (0.02 pound NaOH per pound of 



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POUNDS NaOH PER POUND OF WOOD 



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0URATI0N AT MAX. PRESSURE-HOURS 



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DURATION AT MAX. PRESSURE-HOURS 



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60 70 80 90 100 110 120 

 MAX. PRESSURE-PDS. PER SO. IN. 



40 50 60 70 80 90 100 110 

 CONCENTRATION NaOH-GRAMS PER LITER 



O -TOTAL CRUDE PULP 



• -JCMHED1MUACHED PULP 



F IG- 4.— Effects of cooking conditions on yields of total crude pulp, screened unbleached pulp, and 



screenings. 



wood). The yield at zero caustic soda would probably fall between 

 80 and 90 per cent, being influenced only by the cooking effect 1 of 

 the water condensed from the steam used in cooking. For high 

 amounts of caustic soda the curve tends to approach parallelism 

 with the horizontal axis. The yield would not be expected to become 

 zero unless exceeding^ large amounts of caustic were used. 2 



For amounts of caustic soda above what may be considered the 

 minimum for successful cooking under the conditions used, the yield 



1 See Tauss's experiments, Table 1. 



' Tauss used for a single boiling as high as 7 pounds of caustic soda per pound of wood, and the yield 

 or undissolved material after three hours at 58.8 pounds per square inch steam pressure amounted to 8.52 

 per cent for beech and 2.87 per cent for pine. With 4 pounds caustic soda per pound of wood in each of 

 three successive three-hour treatments under a steam pressure of 132.3 pounds per square inch, the yields 

 for the two woods were 20-61 per cent and 18.20 per cent, respectively. This latter proportion of caustic 

 soda was ten or more times as great as is ordinarily employed in commercial practice. Also tho other 

 cooking conditions wcro proportionately more severe. 



