14 BULLETIN 620, U. S. DEPARTMENT OF AGRICULTURE. 
METHOD OF HANDLING PULP. 
The blow pit was fitted up with a false bottom made of perforated 
tile. The puip was washed five or six times with water and allowed 
to drain each time. When it had been sufficiently washed, it was 
shoveled out into a canvas bag, placed in a perforated iron cylinder, 
and then pressed in a 70-ton knuckle joint power press until it was 
about 30 per cent dry. It was then shredded, so that the bone-dry 
weight determination could be made accurately, weighed, and sam- 
pled for moisture determination. The pressing operation caused the 
pulp to ball or stick together, so that it had to be opened up in the 
beater before it could be screened. This was done with the roll well 
up, after which it was pumped to a stock tank and diluted with water. 
From here it ran upon a six-plate diaphragm screen with slots 0.009 
of an inch in width. After being screened it ran through a stock 
thickener, where most of the water was removed. The screenings 
were carefully collected, pressed, weighed, and sampled for moisture 
determination. Some of the screened pulp was saved for bleach and 
other determinations, after which it was put into a 15-pound Emerson 
beater, mixed with water and beaten, with the roll off the bed plate, 
for one-half hour. The stock was then run into paper over a 15-inch 
Fourdrinier machine and samples of the uncalendered sheets taken 
for strength tests. 
The methods of making the bleach, yield, and strength determina- 
tions are given on page 22. 
EFFECT OF VARYING THE RATIO OF FREE TO COMBINED SO, OR THE 
AMOUNT OF LiME IN THE COOKING LIQUOR. 
In order to determine the effect of varying the ratio of free to 
combined SO,, cooks were made using a liquor with a total sulphur 
dioxide content of 5 per cent and a maximum temperature of cooking 
of 135° C., the amount of SO, combined with lime being varied from 
0.30 to 2.09 per cent. The curves in figure 8 show how variations 
in the combined SO, affected the color rating, duration of cook, 
yield of screened and unscreened pulp, yield of screenings, and bleach 
consumption. 
A decrease in the combined SO,, other conditions being constant, 
has a tendency to shorten the duration of the cooking time. In- 
creasing the amount of combined SO, to 1 per cent has a tendency to 
make the pulp lighter, but the color remains constant when the 
combined SO, is increased over 1 per cent. The color determinations 
for the machine-made sheets were made by means of a tint photometer 
(p. 22). The higher the parts black, the darker the sheet. 
The yield of screenings and unscreened pulp remams constant 
when the combined SO, is decreased to 1 per cent, but any decrease 
below this shows a sharp increase in both of these factors. The 
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