18 BULLETIN 620, U. S. DEPARTMENT OF AGRICULTURE. 



EFFECT OF VARYING TOTAL SULPHUR DIOXIDE. 



Cooks were made varying the amount of total S0 2 from 3.02 to 6.98 

 per cent, but in each case the ratio of free to combined S0 2 was kept 

 at 4 to 1 and the temperature at 135° C. Figure 9 gives the curves 



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PARTS BLACK 



DURATION Of COOK - HOURS 



YIELD Or UNSCREENED 

 PULP - PERCENT 



42 44 46 48 SO 



YIELD OF SCREENED PULP - PERCENT 



I 2 3 4 5 



SCREENINGS-PERCENT 



10 20 

 BLEACH - 



30 40 

 PERCENT 



Fig. 9.— Effect of varying the amount of total S0 2 in the cooking liquor. 



showing the effect on the different factors studied, parts black, dura- 

 tion of cook, yields, and bleach consumed. While these cooks were 

 made with the ratio of free to combined S0 2 of 4 to 1, the actual 

 amount of combined sulphur dioxide in the cooking liquor decreased 

 with the total, as shown in Table 3„ 



