PRODUCING SODA PULP PROM ASPEN. 



57 



AUTOCLAVE TESTS ON ASPEN. 



A few autoclave tests on aspen (Populus tremuloides Michx.) were made in 1909. : 

 The ordinary soda process was employed, but the digester used was a horizontal, rotary 

 autoclave, made of 6-inch steel pipe, with a capacity of about 2 gallons. As the heat 

 was furnished by Bunsen burners, there was no condensation or loss of liquid through 

 overflow to modify the cooking conditions. Cooks were not blown, but the digester 

 was quickly cooled to room temperature and then dumped. The pulps were thor- 

 oughly washed with cold water and screened on a small diaphragm screen through 

 slots of 0.006 inch width. The test material was cut from fairly young growth near 

 Ridgeway, Colo. Portions of the logs tested, especially the centers and around knots, 

 were discolored a dull reddish-brown, probably due to incipient fungous attack; other- 

 wise the wood seemed to be sound. Chips were prepared in the manner described on 

 page 15. Their sizes were five-eighths inch (with the grain) by three-sixteenths to 

 one-fourth inch by one-half in^h to 6 inches (both across the grain). 



The data resulting from the tests are shown in Table 15. The column headings 

 have the same significance as those in Tables 10 to 14, except as otherwise indicated. 

 However, in the bleaching tests the standard color matched was that of bleached 

 sulphite pulp, and, as soda poplar pulp in commercial operations is never bleached 

 to so white a color, the test data should be reduced somewhat in estimating the com- 

 mercial value for bleach required. The values for loss on bleaching also are probably 

 a little greater on this account. 



The tests fall naturally into two groups. One of these consists of cooks 1, 2, and 4, 

 in which the concentration of caustic soda in the cooking liquors was varied. The 

 other consists of cooks 3 and 5, in which the duration at maximum pressure was the 

 chief variable. Increases either of concentration or of duration resulted in decreases 

 in the yield of pulp, loss on bleaching, and bleach required, except possibly in the 

 case of one cook. All of the pulps produced were thoroughly cooked. The yields, as 

 compared with those secured in the more recent tests (see Table 11), were uniformly 

 very low and the losses on bleaching very high. The difference may be due to the 

 methods and apparatus used or to deterioration of the wood from fungous attack, or to 

 both. If the wood had been perfectly sound, it does not seem probable that the lower 

 yields would have been accompanied by the higher amounts of bleach required and 

 the larger losses on bleaching, even though these effects were slightly augmented by 

 the higher standard of bleaching. 



Table 15. — -Cooking conditions and results of autoclave tests on aspen? 





Date of 

 cook. 



Weight 



of chips 



charged 



(bone-dry 



Water 



in 

 chips. 



Liquor charge. 



Initial 



volume of 



digester 



liquors 2 



per 

 pound of 



Chemicals charged per 

 100 pounds of chips 

 (bone-dry basis). 



Cook 

 No. 



Initial concentrations. 2 



Caus- 





















basis). 





NaOH. 



Na 2 C0 3 . 



Total 

 Na 2 0. 



ticity. 



chips 



(bone-dry 



basis).' 



NaOH. 



Na 2 C0 3 . 



Total 

 Na 2 0. 











Grams 



Grams 



Grams 















1909. 



Lbs. 



P.ct. 



per liter. 



per liter. 



per liter. 



P.ct. 



Galls. 



Lbs. 



Lbs. 



Lbs. 



1 



May 25 



1.652 



33.5 



80 



7.4 



66.3 



93.5 



0.375 



25.0 



2.3 



20.7 



2 



May 27 



1.652 



33.5 



50 



1.8 



39.8 



97.5 



.599 



25.0 



.9 



19.9 



3 



June 2 



1.652 



33.5 



90 



4.3 



72.3 



96.5 



.386 



29.0 



1.4 



23.3 



4 



June 8 



1.304 



18.3 



SO 



1.4 



24.1 



96.5 



1.000 



25.0 



1.2 



20.1 



5 



July 3 



1.920 



15.0 



90 



4.3 



72.3 



96.5 



.390 



29.3 



1.4 



23.5 



i These tests were made by Mr. Edwin Sutermeister, formerly in charge of the pulp-testing laboratory 

 of the Forest Service at Washington, D. C. 

 2 The water in the chips when charged is not taken into consideration. 



