14 BULLETIN 620, U. S. DEPARTMENT OP AGRICULTURE. 



METHOD OF HANDLING PULP. 



The blow pit was fitted up with a false bottom made of perforated 

 tile. The pulp was washed five or six times with water and allowed 

 to drain each time. When it had been sufficiently washed, it was 

 shoveled out into a canvas bag, placed in a perforated iron cylinder, 

 and then pressed in a 70-ton knuckle joint power press until it was 

 about 30 per cent dry. It was then shredded, so that the bone-dry 

 weight determination could be made accurately, weighed, and sam- 

 pled for moisture determination. The" pressing operation caused the 

 pulp to ball or stick together, so that it had to be opened up in the 

 beater before it could be screened. This was done with the roll well 

 up, after which it was pumped to a stock tank and diluted with water. 

 From here it ran upon a six-plate diaphragm screen with slots 0.009 

 of an inch in width. After being screened it ran through a stock 

 thickener, where most of the water was removed. The screenings 

 were carefully collected, pressed, weighed, and sampled for moisture 

 determination. Some of the screened pulp was saved for bleach and 

 other determinations, after which it was put into a 15-pound Emerson 

 beater, mixed with water and beaten, with the roll off the bed plate, 

 for one-half hour. The stock was then run into paper over a 15-inch 

 Fourdrinier machine and samples of the uncalendered sheets taken 

 for strength tests. 



The methods of making the bleach, yield, and strength determina- 

 tions are given on page 22 . 



EFFECT "OF VARYING THE RATIO OF FREE TO COMBINED S0 2 OR THE 

 AMOUNT OF LIME IN THE COOKING LIQUOR. 



In order to determine the effect of varying the ratio of free to 

 combined S0 2 , cooks were made using a liquor with a total sulphur 

 dioxide content of 5 per cent and a maximum temperature of cooking 

 of 135° C, the amount of S0 2 combined with lime being varied from 

 0.30 to 2.09 per cent. The curves in figure 8 show how variations 

 in the combined S0 2 affected the color rating, duration of cook, 

 yield of screened and unscreened pulp, yield of screenings, and bleach 

 consumption. 



A decrease in the combined S0 2 , other conditions being constant, 

 has a tendency to shorten the duration of the cooking time. In- 

 creasing the amount of combined S0 2 to 1 per cent has a tendency to 

 make the pulp fighter, but the color remains constant when the 

 combined S0 2 is increased over 1 per cent. The color determinations 

 for the machine-made sheets were made by means of a tint photometer 

 (p. 22). The higher the parts black, the darker the sheet. 



The yield of screenings and unscreened pulp remains constant 

 when the combined S0 2 is decreased to 1 per cent, but any decrease 

 below this shows a sharp increase in both of these factors. The 



