24 



BULLETIN 309, U. S. DEPARTMENT OF AGEICULTURE. 



liberated during the cooking, there is usually more pressure within 

 the digester than the pressure corresponding to the temperature of 

 the charge, and since this false pressure is usually unknown it seems 

 preferable to employ temperature as the control. 

 The results of the tests are shown in Table VII. 



Table VII. — Results of trials of four cooks of zacaton pulp. 





Fiber. 



Relation of 



bone-dry 



fiber. 



Causticity 

 of waste 

 solution. 



Caustic. 



Cook. 



Wet. 



Bone dry. 



Consumed 

 by grass. 



Relation of 

 excess. 



Relation of 

 consumed 

 to added. 





Per cent. 



Pounds. 



No. 11 .^. 



Pounds. 

 686 

 815 

 715 

 730 



22.8 

 20.0 

 20.1 

 19.8 



156 

 163 

 143 



144 



Per cent. 

 50.4 

 49.7 

 47.0 

 46.3 



Per cent: 



Per cent. 



Per cent. 



Per cent. 



No. 12 



No. 13 



No. 14 



35.3 

 38.2 



38.7 



12.0 

 11.5 

 11.4 



8.1 

 8.7 

 8.9 



59 

 56 

 56 



The average yield of fiber at 90 per cent bone dry is 43 per cent of 

 the air-dry grass, which would average 80 per cent bone dry. 



The excess caustic soda, 8.1 to 8.9 per cent of the bone-dry grass, 

 is doubtless higher than is necessary, and it would indicate that less 

 soda could have been employed in the cooking. 



Pulp charges from the four cooks were remarkably similar in 

 appearance and feeling; they drained and washed with great ease, a 

 property not shared by the pulp of many plants and a fact of great 

 importance in a commercial sense, because of the necessity of washing 

 out and recovering the spent soda. 



On screening the pulp charges through a No. 10 cut screen there 

 remained undercooked screenings to the extent of 2.05 per cent of 

 the bone-dry pulp, or 1 per cent of the bone-dry grass. The screened 

 stock bleached easily and to a satisfactory color with the equivalent 

 of 12.7 per cent of commercial bleaching powder. 



After washing free from bleach residues, the stock was given four 

 hours' medium brushing in a beating engine (fig. 13) and furnished with 

 24 per cent of clay, 1.8 per cent of resin size, and 2 per ceJit of alum. 



At the close of the beating operation the charge was whitened by 

 the addition of a small amount of blue or blue and red color, to offset 

 the residual yellow tint invariably present in all bleached stocks. 



The finished stock was run through a Jordan refiner and to a 

 30-inch Fourdrinier machine speeded to 85 feet per minute. Although 

 the stock was a little too ''free" to get the maximum felting of the 

 fiber it acted very well on the machine and gave a machine-finished 

 sheet of good appearance and quality. Physical tests of this sheet, 

 designated as No. 76, in connection with those of sheet No. 41 are 

 given in Table VIII. 



