6 BULLETIN 72, U. S. DEPARTMENT OP AGRICULTURE. 



into the digester or autoclave, the amounts of each chemical per 

 pound of chips (bone-dry basis) was in the desired proportion, and 

 the concentration of chemicals in the digester liquor (including the 

 water in the chips) was of the desired degree. For soda cooks the 

 procedure was similar, except that caustic soda was the only chemical 

 to be taken into consideration. The general procedure in conducting 

 the tests was as follows : 



The chips to be used for a cook were sampled and weighed. By 

 means of the sample the amount of moisture in the chips and the 

 equivalent bone-dry weight of the charge were determined. The chips, 

 together with the cooking liquors, were then charged into the auto- 

 clave or digester, and the vessel closed. After a cook was completed 

 the crude pulp obtained was washed thoroughly, pressed to remove 

 water, shredded, weighed, and sampled for determining its equivalent 

 bone-dry weight. The pulp was then mixed with water and treated 

 in a Hollander-style beating engine 1 with the roll barely touching 

 the bedplate (light brush) until the soft chips in the pulp had 

 become disintegrated into fibers and the wet fibers had a smooth, 

 slippery feel. The beater roll was then pressed hard down on the 

 bedplate (stiff brush), and the beating operation continued until 

 the pulp was suitable for making wrapping paper, as determined by 

 its "feel." The beaten pulp was then screened through the slots 

 (0.012 inch width) of a diaphragm pulp screen. In all cases the 

 screenings obtained were so small in amount that they were dis- 

 regarded in the yield calculations. The semicommercial pulps were 

 run over a Pusey and Jones 15-inch Fourdrinier paper machine into 

 rolls of dry paper, while the autoclave pulps were made up into sheets 

 on a small hand mold. The papers thus produced contained the 

 experimental pulps alone, without the addition of any other materials. 



DETERMINATION OF YIELDS AND PROPERTIES. 



The yield of pulp (bone-dry basis) is usually expressed as a per- 

 centage of the bone-dry weight of the chip charge, both weights 

 being determined as explained above. When yields per cord are 

 given they are based on a "solid cord" containing 100 cubic feet of 

 clear wood (green volume) having a bone-dry weight of 35.5 pounds 

 per cubic foot; 2 or 3,550 pounds per cord. 



The strengths of the papers from the semicommercial pulps were 

 determined by means of a Mullen paper tester, five "pop tests" being 

 made on double thicknesses of each paper. The value is expressed 

 as a "strength ratio/' which is the average of the five test values in 

 pounds per square inch divided by the average sheet thicknesses 



1 A 25-pound Emerson beater was used for the semicommercial tests and a 1-pound Noble and Wood 

 beater for the autoclave tests. Both makes were equipped with steel fly bars and steel bedplate bars. 



2 This was the average bone-dry weight of the two butt logs of long leaf pine from Louisiana, the 

 material used in the tests for which yields per cord are given. 



