PRODUCTION OF SULPHITE PULP FROM SPEUCE. 21 



decrease in the amount of bleach consumed, as indicated by the curve. 

 This is rather surprising when one considers that the yield of screened 

 pulp increased almost 5 per cent, while the bleach decreased from 22 to 

 1 1 per cent. This must be due to the more uniform cooking occurring 

 at the lower temperatures so that broken up, uncooked shives did not 

 consume bleach. The values for strength are fairly regular (Table 3), 

 probably as a result of the use of an improved style of beater in this 

 series. As would be expected, they show an increase in strength 

 with decrease in temperature. 



Photomicrographs of the pulps produced in cooks 90, 92, 97, and 

 100 are shown on Plates IX, X, XI, and XII. Cook 90, which was 

 made with a high temperature, contains much lignified fiber and is 

 not very uniform; while cook 100, which was made at a low tempera- 

 ture, seems to be well cooked and has fibers nearly all of the same 



length. 



SUMMARY OF RESULTS. 



1. These experiments have demonstrated that a standard color 

 can be used with which to match the color of the liquor in the digester 

 to determine when a cook is finished. A cook can be duplicated at 

 any time by comparison with this standard. 



2. The limit to which the combined S0 2 can be decreased to obtain 

 good cooking seems to be about 1 per cent. Below this there is a 

 rapid darkening of the pulp produced, and an increase in the screen- 

 ings and bleach consumed. 



3. When the temperature and total S0 2 are kept constant, the yield 

 of screened pulp increases somewhat with increase in the combined 

 S0 2 , because of the more thorough cooking. Consequently, less 

 screenings are obtained. 



4. When the temperature and total S0 2 are kept constant, a de- 

 crease in the amount of combined S0 2 causes quicker cooking action, 

 so that a cook can be finished in less time. 



5. An increase in the total S0 2 causes a decrease in the cooking 

 period, other factors remaining constant. 



6. The screenings and color of the pulp remain constant as the 

 total S0 2 is decreased to about 5 per cent, after which there is a rapid 

 increase in both of these factors. 



7. The higher the total S0 2 , the easier it is to bleach the pulp, 

 other factors being the same. 



8. The amount of screenings decreases as the temperature is lowered, 

 because of the more even cooking obtained at the lower tempera- 

 tures. 



9. The bleach is reduced as the temperature is decreased, while the 

 yield of pulp increases. 



