12 
BULLETIN 1485, U. S. DEPARTMENT OF AGRICULTURE 
pressure and temperature were carefully regulated and observations 
recorded at 15-minute intervals. At the end of the cooking period 
samples of liquor were taken and, in the case of sulphite cooking, 
analysis was made and color observed. The digester contents 
were then discharged into the blow pit. There the pulp was washed 
free of cooking liquor and drained. In the case of impregnation 
cooks the digester was completely filled with chips and cooking 
Fig. 3.— Digester used for sulphite cooks since 1916 (end elevation) 
liquor and the cover bolted on. The pressure tank, I in Figure 3, 
was next filled, and, by forcing steam into the top of I and opening 
the connections therefrom to the digester, hydrostatic pressure was 
set up around the chips, forcing the liquor into them until at the end 
of from 15 to 30 minutes at a pressure of from 100 to 110 pounds 
to the square inch they were well penetrated. The digester was 
then inverted, the valves in the relief pipe L and pipe O (fig. 4) 
were opened, and the proper quantity of liquor was blown back 
