Chemistry of pulp and paper making . nzellstoff, Berlin, 1913. io6 THE SODA PROCESS A study of the effect of steam pressure in semi-coimnercialcooks (400 lbs. chips) in a vertical, stationary digester gaveresxilts follovnng very closely the form of curve of the small-scale cooks. The yields were, however, 8 to 9 per cent we wo 80 60 a 6 40 •33 35 .37 Per ceut yield Fig. II. 39 a 43 greater, which appears to be a characteristic difference betweenthe vertical digester and the smaU rotary heated by a gasflame. The influence of the initial concentration of caustic soda inthe cooking liquor is show
Chemistry of pulp and paper making . nzellstoff, Berlin, 1913. io6 THE SODA PROCESS A study of the effect of steam pressure in semi-coimnercialcooks (400 lbs. chips) in a vertical, stationary digester gaveresxilts follovnng very closely the form of curve of the small-scale cooks. The yields were, however, 8 to 9 per cent we wo 80 60 a 6 40 •33 35 .37 Per ceut yield Fig. II. 39 a 43 greater, which appears to be a characteristic difference betweenthe vertical digester and the smaU rotary heated by a gasflame. The influence of the initial concentration of caustic soda inthe cooking liquor is shown in Fig. 11. Decreasing the con-centration increases the yield sUghtly but this factor is evidenflyof less importance than the steam pressure since increasing SODA ADDED 107 from 80 to 100 grams per liter reduces the yield only per cent. Fig. 12 shows the variation in yield and bleach required withchanges in the per cent of caustic soda added. With 22 per centof caustic the yield was high but the fibre was unsatisfactory. 24 28 32 36 40 Per cent Tield11 15 19 Per cent Bleach Fig. 12. 44 48 23 27 31 in that it was commercially unbleachable. Increasing the caus-tic to 28 per cent decreased the yield very greatly but producedeasy bleaching fibre. When the caustic is brought up to 40 to50 per cent of the weight of wood the form of curve suggeststhat its maximum cooking effect is nearly reached. This curveshows why 25 per cent of caustic soda is the most satisfactoryfor commercial work since if more is used the yield is too greatlyreduced while if much less is employed the bleach required io8 THE SODA PROCESS increases to an excessive amount. Evidently the percentage ofcaustic soda is one of the most important points to watch inthe control of the soda process. The influence of time under pressure is shown in Fig. 13,where cooks ranging from three to nine hours are recorded. Therate of decrease in yield is not the same for equal intervals of Per cent Bleacfi5 6 7 8 9 1 \
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