22 



BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. 



EFFECTS OF VARYING THE DURATIONS OF COOKING. 



Since the tirne 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 varying 

 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 amounts of chemicals, 55.9 per cent of the wood 

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

 cooking, while 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. 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 



Total duration of beater treatment (at light brush only) hours.. 1.5 or 2 



FIRST SERIES. 



SECOND SERIES. 



THIRD SERIES. 



i The same values apply to the Na 2 SOrf used. 



(P. L. 138, S. L. 176.) 



