10 



BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. 



rubbed or crumpled for a long time without becoming fuzzy, tearing, 

 or showing signs of wear at the place of friction. The papers had also 

 a soft, smooth, greasy, leather-like feel, and were light brown in color, 

 like the imported kraft papers. The yields were rather low for 

 sulphate kraft pulps. For cook 77 the yield was 45.3 per cent, or 

 1,609 pounds per solid cord, and for cook 141, 44.2 per cent, or 1,569 

 pounds per solid cord. Under still more severe cooking treatments 

 longleaf pine pulps become very soft and gradually lose their strength 

 and wearing properties. (See autoclave tests, p. 14-24.) 



MEDIUM COOKING TREATMENTS. 



The above-mentioned cooks show approximately the higher and 

 lower limits of yield in the production of pulps and papers of good 

 quality. However, the better quality of wrapping papers resulted 

 from pulps having the lower yields, and in attempting to secure this 

 better quality, but with higher yields than were obtained for cooks 77 

 and 141, cooks 85, 98, and 146 were made. For cook 85 the amounts 

 of chemicals and the initial concentrations were decreased from the 

 corresponding conditions for cook 77, while the duration of cooking 

 and the pressure remained practically the same; for cook 98 a further 

 decrease was made in the amounts of chemicals and in the concen- 

 trations, but the duration of cooking was increased; for cook 146 the 

 amounts of chemicals and the duration were practically the same as 

 for cook 85, but the concentrations were decreased while the pressure 

 was increased. The cooking conditions, given in full in Table 1, are 

 briefly summarized in Table 2. The resultant papers were in each 

 case of good quality, being tough and resistant to wear, but they were 

 in general not so strong as those from pulps produced under more 

 severe cooking treatments. The strength factors for cooks 85, 98, 

 and 146 were 0.87, 0.56, and 0.68, respectively. There is little doubt, 

 however, that these values could be increased considerably by 

 employing beating and other refining treatments better adapted for 

 these particular pulps than the treatments given them. The yields 

 obtained were quite high, cook 85 yielding 52 per cent, or 1,846 

 pounds per solid cord; cook 98, 51.8 per cent, or 1,839 pounds per 

 solid cord; and cook 146, 54.9 per cent, or 1,949 pounds per solid cord. 



TABLE 2. Condensed summary of cooking conditions for cooks 77, 85, 98, and 146. 



