22 



BULLETIN 72, U. S. DEPARTMENT OF AGEICULTUEE. 



EFFECTS OF VARYING THE DURATIONS OF COOKING. 



Since the time from the start of a cook until maximum pressure was 

 obtained in the autoclave was practically constant (varying from 

 0.5 to 0.7 hour), only the total duration of cooking will be considered. 

 Table 9 shows how the yields were affected for total durations varjdng 

 from one to nine hours in three series of tests, using high, medium, 

 and low amounts of chemicals. In the case of the first series, em- 

 ploying very high amoimts of chemicals, 55.9 per cent of the wood 

 (giving a yield of 44.1 per cent) was dissolved during two hours of 

 cooking, wliile by cooking for seven hours longer an additional loss 

 of only 12.8 per cent occurred. Cook 124, with a total duration of 

 but one hour, afforded the best pulp and the highest yield for this 

 series. This pulp came from the autoclave in the form of soft chips, 

 and the resultant paper made from the beaten pulp was firm and 

 strong, with good resistance to wear. The other pulps were soft 

 and fuzzy, due to overcooking. As the duration increased, the 

 color of the pulps changed from brown (cook 124) to light gray 

 (cook 78). 



Table 9. — Effect of varying durations of cooking on the yield of pulp. 



Weight of chips charged (bone-dry basis),. . . ^ pounds. . 0. 964 to 1. 034 



Water in chips per cent ..16.0 to 24. 4 



Causticity of liquor charge do 51.6 to 53. 3 



Sulphidity of liquor charge do 26. 5 to 27. 4 



Initial volume of digester liquors per pound of chips (bone-dry basis) gallons . . 0. 667 to 0. 680 



Duration of cooking at zero gauge pressure hours. . 0. 1 



Maximum gauge pressure per square inch pounds. . 90 



Totaldurationofbeatertreatment(dtlightbrushonly) hours.. 1.5 or 2 



FIRST SERIES. 





Liquor charge, initial concen- 

 trations. 



Chemicals charged per 100 

 pounds of chips (bone-dry 

 basis). 



Duration of cooking. 



Yield of 



crude 



pulp 



(bone-dry 



basis). 



Cook 



No. 







All 

 sodium 







All 

 sodium 





At maxi- 





NaOH.- 



Na2S.i 



com- 



NaOH. 



NaaS.i 



com- 



Total. 











pounds 







pounds 















as Na20. 







as Na20. 











Orams 



Grams 



Grams 

















per liter. 



per liter. 



per liter. 



Pounds. 



Pounds. 



Pounds. 



Hours. 



Hovrs. 



Per cent. 



124 



71.9 



36.0 



104.7 



40.0 



20.0 



58.3 



1.0 



0.5 



57.4 



125 



71.9 



36.0 



104.7 



40.0 



20.0 



58.3 



2.0 



1.5 



44.1 



80 



72.0 



36.0 



104.7 



40.0 



20.0 



58.2 



5.0 



4.3 



37.8 



78 



72.0 



36.0 



108.1 



40.0 



20.0 



60.1 



9.0 



8.3 



31.3 



SECOND SERIES. 



123 



44.9 



22.5 



65.4 



25.0 



12.5 



36.4 



1.0 



0.5 



68. 6 



126 



44.9 



22.5 



65.4 



25.0 



12.5 



36.4 



2.0 



1.5 



4S. 5 



84 



45.0 



22.7 



&5.6 



25.0 



12.6 



36.5 



5.0 



4.3 



45.0 



83 



45.0 



22.7 



65.6 



25.0 



12.6 



30.5 



9.0 



8.3 



38.2 



THIRD SERIES. 



86 



21.6 



10.8 



31.4 



12.0 



6.0 



17.4 



1.0 



0.3 



80.9 



127 



21.0 



10.8 



31.6 



12.0 



6.0 



17.6 



2.0 



1.5 



00.7 



88 



21.2 



10.6 



30.8 



12.0 



0.0 



17.4 



5.0 



4.3 



59.0 



87 



21.6 



10.8 



31.4 



12.0 



0.0 



17.4 



9.0 



8.3 



57.0 



1 The same values apply to the NajSOi used. 



(P. L.— 138, S. L.— 176.) 



