12 BULLETIN 620, U. S. DEPARTMENT OF AGRICULTURE. 
curve 4 shows the steam pressures corresponding to the tempera- 
tures. Curve 2 shows the gauge pressure, and curve 3 shows the 
gas pressure, which is the difference between the gauge pressure and 
the steam pressure at any given pomt. Endeavor was made to keep 
the temperature curve a straight line, but sometimes the tempera- 
ture would drop and then to reach the desired temperature the observer 
would turn on full pressure of steam, which caused a rapid increase 
in the gauge pressure and accounts for some of the bulges in the gas and 
gauge pressure curves. Every 15 minutes readings were taken of the 
temperature and pressure. Owing to the peculiar type of construc- 
tion of the digesters and the position of the thermometer well, it was 
necessary at the end of about two and one-half hours of cooking to 
inject steam into the digester to make up for the liquor taken up by 
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Fic. 7.—Cooking curves for cooks 97 and 100. 1, temperature; 2, gauge pressure; 3, gas pressure; 4, steam 
pressure. 
the chips, or the liquor level would smk below the thermometer well 
and not give the correct reading. This was done as uniformly as 
possible for every cook. 
METHOD OF FINISHING COOK. 
With the composition of liquor and temperature changing each 
time, a great deal of difficulty was experienced at first in knowing 
when to finish cooks so that each one would be pulped to the same 
degree. The digester was equipped so that cold liquor for sampling 
could be obtained by passing it through a condenser. 
An attempt to finish cooks to the same sulphur dioxide content 
was made, but some would be overcooked while others would be 
almost raw, as a result of using liquor containing different amounts 
of SO,. This method can only be used when the same kind of liquor 
