PRODUCTION OF SULPHITE PULP FROM SPRUCE. 19 
The curve for parts black shows that after a total of 5 per cent is 
reached, any increase in the total SO, does not produce a lighter 
pulp, but below that point there is a rapid darkening. An increase in 
the total SO, causes a shortening in the cooking time, as would be 
expected. The yield of unscreened pulp and screenings shows a 
decrease as the total SO, is increased, which becomes only slight as a 
total SO, of 5 per cent is reached. The yield of screened pulp remains 
‘practically constant, because even if the amount of unscreened pulp 
is increased as the total SO, is decreased, the amount of screenings 
increases in almost the same amount. An increase in the total SO, 
causes a decrease in the amount of bleaching powder necessary to 
bleach the pulp-to a standard white. Below 4 per cent there is a 
rapid increase, while above that point there is a gradual decrease in 
the bleaching powder necessary. The strength tests in this series 
as in the previous one, were unfortunately very irregular and no con- 
clusions could be arrived at from them. 
A study of the curves shows that below 5 per cent total SO, there 
is a decided effect on some of the factors studied. At 5 per cent total 
SO, the liquor had a combined SO, of 1.01 per cent; and at the 4 and 5 
per cent total SO,, a combined SO, of 0.80 and 0.61 per cent, showing 
again that as we go below 1 per cent in combined sulphur dioxide, the 
parts black, the amount of screenings, and the bleach consumed 
rapidly increase, for the reason that there is less cooking action. 
Photomicrographs of the pulps obtained in cooks 81, 86, 87, and 89 
are shown on Plates V, VI, VII, and VIII. Cook 81, which was made 
with a high total SO,, is more thoroughly cooked than cook 89, which 
was made with a low total. The latter contains much lgnified fiber, 
the result of having the low percentage of lime in the liquor. 
EFFECT OF VARYING THE TEMPERATURE OF COOKING. 
To study the effect of variations in temperature, cooks were made 
using an acid of the same composition in each case, but varying the 
temperature from 110° to 146° C. Figure 10 shows the effect on 
parts black or color of the pulp, on duration of cook, on yields of 
pulp and screenings, and on amount of bleaching powder necessary 
to bleach the pulp to a standard white. 
Varying the temperature has little or no effect on the color of pulp 
produced. The duration of cooking rapidly increases as the temper- 
ature is lowered, and apparently there would be very little cooking 
action under 110°C. At146°C. the cook finished im a little over 5 
hours, while at 110° it took almost 25 hours. The yields of screended 
and unscreened pulp both increase as the temperature is lowered, 
especially between 120° and 110°, where there is an increase of almost 
3 per cent. In the other 10-degree periods the increase amounts to 
