PRODUCTION OF SULPHITE PULP FROM SPRUCE. 5 
and smell of the liquor, and how accurately it is attained depends in 
most mills wholly on the experience and judgment of the man in 
charge of the cook, When the cook is finished, a large valve is opened 
at the bottom of the digester and the contents blown through a pipe 
into a blow pit, where they are thoroughly washed. 
In the slow cook process the digester is heated by lead coils placed 
in the bottom. Because of the caking of calcium monosulphite on 
them, however, these are rapidly going out of use and the heating is 
being done by direct steam. A somewhat weaker acid is used than 
for the short cook, and the pressure is held at from 60 to 65 pounds. 
A cook lasts from 20 to 30 hours, but the digesters are much larger 
than in the quick-cook process and the pulp is much stronger and 
the fibers longer. Otherwise the process of cooking is the same. 
PLAN OF TESTS. 
In the experiments recorded in this bulletin, the following factors 
were studied for the effect of variations in them on duration of 
cooking, yield of pulp, yield of screenings, bleach consumed, color of 
pulp produced, and strength. 
1. Ratio of free to combined sulphur dioxide, or the amount of 
lime in the cooking liquor. 
2. Total sulphur dioxide. 
3. Temperature of cooking. 
While one factor was studied the other two were kept as constant 
as possible. For instance, when the effect of temperature was being 
studied, cooks were made with definite variations in temperatures, 
but the consumption of the cooking liquor remained the same. Of 
course, the following factors were kept constant for all the cooks: 
Amount of chips, 74.2 pounds bone dry; moisture condition of chips, 
air dry; amount of acid, 63 gallons; time to reach 100° C., 2 hours; 
time to reach maximum temperature, 3 hours. 
APPARATUS. 
A plan of the apparatus used in cooking is shown in figure 2. The 
digester was lined with a half and half mixture of special cement and 
quartz sand. This lning was about 14 inches thick, and on top of 
it was put a layer of pure cement 1 inch thick. 
The equipment used for making the pulp into paper consisted of a. 
pulp shredder, 15-pound Emerson beater, 6-plate diaphragm screen 
with 0.009-inch slots, and a 15-inch Fourdrinier paper machine. A 
50-pound Marx beater was used on the last six cooks. 
The wood used in these experiments was white spruce (Picea 
canadensis) cut in the State of Wisconsin. ‘This wood was cut into 
five-eighths-inch chips in a small chipper of the usual design and the 
chips screened, after which they were ready for the digester. 
