PRODUCTION OF SULPHITE PULP FROM SPRUCE. 13 
is used for every cook. What is ordinarily known as the lime test 
was also tried. In this test some of the cooking liquor from the diges- 
ter was put m a test tube containing a slight excess of ammonia, 
and if the ime came down in a dark floculent condition it was time 
to blow the cook. While this method gave promise, the results ob- 
tamed with it were very erratic and it was finally abandoned. An 
attempt to judge the degree to which the chips in the digester had 
been cooked by blowing some out into a canvas bag and shaking in 
a cylinder was also unsuccessful because of the great irregularity in 
the samples. Sometimes a sample would show more uncooked shives 
than the one taken half an hour before. Judging the condition of 
the stock by dyeing with a basic color, such as diamond green, also 
showed no regularity. Nor did the depth to which a 13 per cent 
solution of nitric acid would color the pulp indicate the end point 
accurately. 
It is common practice in pulp mills to judge when a cook is finished 
by the color, smell, and analysis of the liquor; but with the wide 
variety of conditions under which the cooks in this study were made 
it was at first thought that these methods would not be applicable. 
However, it was decided to give the color method a trial. The liquor 
in. the digester near the end of the cook has a light caramel color 
which darkens rapidly on standing. 
To finish a series of cooks to the same degree of cooking it is neces- 
sary to have some fixed color as a standard for comparison. Most 
solutions of organic dyes change in color rapidly when exposed to 
the light and no combination of mineral dyes could be made that 
would match the color wanted close enough. The color desired 
strongly resembles the color of coffee extract, and it was decided to 
see if this could not be made permanent enough to run a series of 
cooks. Two solutions, which had been clarified with the white of 
an ege, were made, one light and one dark, and the shade desired 
was matched up as closely as possible by mixing the two. Formal- 
dehyde solution was then added to stop fermentation and no change 
- in color of the coffee extract was perceptible, even after it had been 
in use for several months. The results obtained by using this stand- 
ard were satisfactory from the first. All that is necessary to duplicate 
a certain. cook is to match the color of the liquor at time of finishing 
with coffee extract to be used as a standard. This ought to find 
application commercially, as the man in charge will not have to 
depend on his memory when he wishes to duplicate a certain cook. 
During the progress of the cook, samples of the liqour were with- 
drawn. from time to time in a test tube and the color compared with 
the standard. When the color matched, the steam to the coil was 
turned off, the pressure in the digester relieved to 70 pounds in five 
minutes, and the cook blown into the blow pit. 
