20 



BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. 



chloride has an effect on the yield, as is evidenced by the data for 

 cooks 128 and 137. Both cooks employed 20 pounds of caustic soda 

 per 100 pounds of wood, but the former used 5 pounds of sodium 

 chloride in addition. The yields from the two cooks were identical. 

 The use of sodium chloride appeared to improve the qualities of the 

 pulps somewhat, but they were much inferior to sulphate pulps at 

 similar yields. The few advantages attending the use of sodium 

 chloride preclude the possibility of this modification of the soda 

 process being of commercial value. 



TABLE 7. Effect of sodium chloride (NaCl) used in conjunction with caustic soda (NaOH) 



on the yield of pulp. 



Weight of chips charged (bone-dry basis) pounds. . 0. 910 to 1. 043 



Water in chips per cent. . 15. 1 to 22. 



Causticity of liquor charge (disregarding NaCl) do 96. to 97. 2 



Duration of cooking at zero gauge pressure hours. . 0. 1 



Maximum gauge pressure per square inch pounds. . 90 



Total duration of beater treatment (at light brush only) hours . . 2 



(P. L. 138, S. L 176.) 

 i The values shown represent common table salt and not the pure chemical. 



EFFECTS OF SULPHUR. 



Cooks using "flowers of sulphur" and caustic soda as the cooking 

 chemicals produced pulps almost identical with those resulting from 

 the sulphate process. The addition of sulphur undoubtedly im- 

 parted to the pulps the resistance to wear and strength not obtainable 

 by the soda process alone. These cooks, however, were character- 

 ized by the same disagreeable odor as the sulphate cooks, and this 

 modification of the soda process seems to have no particular tech- 

 nical advantage over the sulphate process except in the matter of 

 control of the cooking liquors. 



EFFECTS OF VARYING THE PRESSURES OR TEMPERATURES OF COOKING. 



In the sulphate process, as in the soda process, the digester pres- 

 sures represent the pressure of saturated steam, since no other 

 gases are present in sufficient quantity to affect the pressure. This 



