PRODUCTION OF SULPHITE PULP PROM SPRUCE. 19 



The curve for parts black shows that after a total of 5 per cent is 

 reached, any increase in the total S0 2 does not produce a lighter 

 pulp, but below that point there is a rapid darkening. An increase in 

 the total S0 2 causes a shortening in the cooking time, as would be 

 expected. The yield of unscreened pulp and screenings shows a 

 decrease as the total S0 2 is increased, which becomes only slight as a 

 total S0 2 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 S0 2 is decreased, the amount of screenings 

 increases in almost the same amount. An increase in the total S0 2 

 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 S0 2 there 

 is a decided effect on some of the factors studied. At 5 per cent total 

 S0 2 the liquor had a combined S0 2 of 1.01 per cent; and at the 4 and 5 

 per cent total S0 2 , a combined S0 2 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 S0 2 , is more thoroughly cooked than cook 89, which 

 was made with a low total. The latter contains much lignified 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. At 146° C. the cook finished in 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 



