PRODUCTION OF SULPHITE PULP FROM SPRUCE. 15 
yield of screened pulp increases as the combined SO, is increased to 
1 per cent, but beyond this remains constant. The amount of 
bleaching powder necessary to bring the pulp to a standard white 
decreases as the combined SO, is increased to about 1 per cent, but 
2.4 
ComBinen SOz — PERCENT 
re) Ee Lt 
80 120 160 260 0 10 20 30 44 46 &8 $8 
PARTS BLACK DURATION GF COOK—HOURS VIELD OF URSCREENED 
PULP — PERCENT 
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42 44 46 48 50 Q 1 2 3 4 $ 0 10 )6200—C— 30 Ds SN 
YIELD OF SCREENED PULP — PERCENT SCREENINGS-PERCENT BLEACH—PERCENT 
Fic. 8.—Effect of varying the amount of combined SO, in the cooking liquor. 
any increase beyond this point does not produce any further change 
in color. 
The amount of combined SO, does not seem to have much influence 
on the different factors studied, provided it is over 1 per cent, but 
any decrease below this caused marked changes in the character and 
