18 BULLETIN 72, U. S. DEPARTMENT OF AGRICULTUEE. 



the maximum gauge pressure was 100 pounds per square inch. The 

 product came from the autoclave in the form of hard, black chips 

 which were quite "raw" on the inside; the yield was not determined. 

 In comparison with this result, cook 40 (Table 6), using, per 100 

 pounds of wood, 10 pounds of caustic soda, 5 pounds of sodium sul- 

 phide, and 5 pounds of sodium sulphate (the latter being of no 

 assistance in cooking), also afforded a product in the cliip form. 

 These chips, however, were soft, and could easily be picked apart with 

 the fingers. Of the 3 hours' total duration for this cook, 2.3 hours 

 were at a maximum pressure of 90 pounds. The yield was 65.7 per 

 cent. Wliile it is hardly safe to base a general conclusion upon a single 

 trial, tliis test indicates that sodium carbonate, at least when present 

 in considerable quantity, retards or diminishes the effects of the 

 caustic soda and sodium sulphide. 



EFFECTS OF SODIUM SULPHATE. 



Sodium sulphate is present in the commercial cooking liquors, due 

 to incomplete reduction of the sulphate to sulphide during the smelt- 

 ing operations. Like sodium carbonate, it is of practically no assist- 

 ance in cooking. A cook of 3 hours' duration and 90 pounds maxi- 

 mum gauge pressure was made, using sodium sulphate in the propor- 

 tion of 50 pounds per 100 pounds of wood, which yielded 86.3 per cent, 

 while another cook of the sarne duration and pressure but without 

 any chemicals whatever (that is, using pure water alone) had a yield 

 of 89.1 per cent. Allowing for experimental errors, there was little 

 difference between the results of these two cooks, and in neither case 

 could the product be beaten into pulp. 



A cook was also made, using 40 pounds of sodium sulphate, 10 

 pounds of caustic soda, 5 pounds of sodium carbonate, and 5 pounds 

 of sodium sulphide per 100 pounds of wood; the duration was eight 

 hours and the maximum gauge pressure was 100 pounds per square 

 inch. Only hard black chips were obtained, of no value whatever 

 for pulp. As in the case of the sodium carbonate, there is an indica- 

 tion that sodium sulphate retards the action of the other chemicals. 

 To prove this further tests are necessary. 



EFFECTS OF VARYING ^LL CHEMICALS IN SAME PROPORTION. 



A series of tests was made varying the amounts of all sodium com- 

 pounds present in sulphate cooking liquors. The several constituents 

 were kept constant in regard to each other in the proportion of 50 

 parts caustic soda, 25 parts sodium sulphide, and 25 parts sodium 

 sulphate. For convenience the amounts of the different chemicals 

 have been computed to a common basis, and the combined values are 

 expressed as NajO (sodium oxide). 



