10 



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



The tests fall naturally into four groups; in each group all the condi- 

 tions were held as nearly constant as possible except the factor under 

 investigation, which was varied in successive tests or "cooks" accord- 

 ing to a definite plan. The plan of the tests is shown in Table 3. In 

 addition to the factors mentioned in this table all other factors under 

 control were so far as possible held constant. Those for which values 

 were specified are the following: 



Amount of chips for each charge, 40 pounds bone-dry weight. 



Dryness of chips, air dry. 



Causticity of cooking liquors, 95-98 per cent. 



Temperature of charging cooking liquor, 22° C. (72° F.) 



Temperature of digester room, 22° C. (72° F.) 



Duration of cooking before maximum pressure is reached, 1 hour. 



Duration of cooling and relieving digester before blowing, 5-10 minutes. 



Blowing pressure, 30 pounds per square inch. 



Table 3. — Plan of cooking experiments. 





Num- 

 ber of 

 tests. 



Cooking conditions under investigation. 



Test 

 group. 



Initial concentration 

 of caustic soda in 

 digester liquors. 1 



Amount of caustic 

 soda per 100 

 pounds of wood. 1 



Maximum cooking 

 temperature 

 (equivalent steam 

 pressure). 



Duration of cooking 

 at maximum pres- 

 sure or tempera- 

 ture. 



I. 



II. 



III. 



6 

 6 



6 



4 



Constant — SO grams 

 per liter. 



Same as Group I 



do 



Variable — from 15 

 to 40 pounds in 

 steps of 5 pounds 

 each. 



Constant— 25 pounds 

 (value selected 

 from Group I tests 

 as most satisfac- 

 tory for later tests). 



Same as Group II . . . 



do 



Constant — 100 

 pounds per square 

 inch. 



Same as Group I 



Variable— from 70 to 

 120 pounds per 

 square inch in 

 steps of 10 pounds 

 each. 



Con stan t—1 

 pounds per square 

 inch (value se- 

 lected from Group 

 III tests as most 

 satisfactory for 

 later tests). 



Constant— 6 hours. 



Variable — from 1 to 

 11 hours in steps 

 of 2 hours each. 



IV. 



Variable— from 110 



to 50 grams per 

 liter in steps of 20 

 grams each. 



(value selected 

 from Group II tests 

 as most satisfac- 

 tory for later tests). 

 Same as Group III. 







iln commercial practice it is customary to vary the amount of chemical used and its initial concentra- 

 tion both at the same time when attempting to change the severity of the cooking due to these factors. 

 This results in the volume of the cooking liquors being kept approximately the same, which is a desirable 

 feature. In these tests, however, it was the intention to find out the effects of each factor separately. 



TESTING PROCEDURE. 



The apparatus employed in cooking is shown in figure 1. Figure 

 2 shows diagrammatically the course of the material through the 

 various stages of treatment and testing, and in this way the relation 

 of one part of the procedure to another is made clear. 



After the amount of moisture in the chips had been ascertained 

 by means of sample A, the charge was weighed out and put into the 

 digester. Caustic soda solution, of the desired concentration and 

 volume, had been prepared by diluting the necessary Quantity of 

 analyzed stock solution (sample B) with water. It was then heated 



