54 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



METHODS FOR AUXILIARY TESTS. 



In determining bone-dry weights, properties of pulps, and concentrations of soda 

 liquors, the following methods were employed: 



BONE-DRY WEIGHTS. 



In practically all determinations involving exact quantities of wood, pulp, or 

 screenings, either actual or calculated bone-dry weights were used. The actual 

 bone-dry weight is the weight of the material after having been dried to constant 

 weight in an oven with good circulation of pure air at a temperature of 104-106° C. 1 

 Usually instead of drying the entire quantity of material, its "bone-dry factor," or 

 the ratio of the bone-dry weight to the weight before drying, was determined by 

 means of a small sample. The calculated bone-dry weight is the weight obtained 

 by use of this factor. The errors in calculated bone-dry weights were found by actual 

 test to be less than 0.3 per cent. 



PROPERTIES OF UNBLEACHED PULP. 



Color. — The color of a pulp was determined by visual observation and also by 

 means of an Ives new construction tint photometer. The standard for comparison 

 was a block of magnesium carbonate, which affords photometer readings of 100 each 

 for the red, green, and blue color screens used. The sum of the three readings for 

 a pulp measures its "whiteness," and this sum subtracted from 300 2 (the sum of the 

 three readings for a surface as white as the standard) measures the "parts black" rat- 

 ing of the pulp. The higher the "parts black" value the darker is the pulp. This 

 method of expressing relative "darkness" of different pulps is reliable only when 

 the pulps are of approximately the same hue, as in the case of these experiments. 



Skives. — Shives in pulp are the small bundles of wood fibers which were not reduced 

 by the cooking and subsequent operations, and which were not removed by the pulp 

 screens. For the determination, a three-tenths-gram portion of pulp, the bone-dry 

 factor of which was known, was thoroughly broken up in a small Erlenmeyer flask 

 and deposited on a 70-mesh sieve in an even deposit or sheet covering 9.66 square 

 inches. This sheet was "couched" on a silk cloth and then transferred to a glass 

 plate and dried in an oven. When the plate with the deposit was placed in front of 

 an incandescent lamp the shives could easily be counted with the eye. In cases 

 where the number was large, a glass plate divided into quarter-inch squares was 

 placed on top of the pulp and a small area was examined instead of the whole. Know- 

 ing the area examined and the bone-dry weight of the pulp sheet, the number of 

 shives per gram of bone-dry pulp could be calculated. 



Ash. — The ash was determined by burning a bone-dry sample of unbleached pulp 

 of known weight in a platinum or porcelain dish over a Bunsen flame until the ash 

 produced was free from carbon and of a white or grayish-white color. The percentage 

 of ash is based on the bone-dry weight of the pulp. 



Strength. — The strength of the pulp sheets made on the paper machine was deter- 

 mined by a Mullen paper tester and by a Schopper breaking-length testing instrument. 

 The pulp was tested in the ordinary air-dry state for the conditions that prevailed 

 in the laboratory. The Mullen test, or "pop test" as it is sometimes called, was 

 made by clamping a single sheet, accurately measured for thickness, between a rubber 

 diaphragm and a polished metal ring, and then, by means of liquid under pressure, 

 forcing the diaphragm against the pulp sheet until it burst through the aperture. 

 The pressure on the liquid in pounds per square inch, or "points," is read from a 



1 The weight was considered constant when the decrease was not more than 0.1 per cent during an addi- 

 tional hour's drying at this temperature. 



2 At the time of these experiments the shutter of the instrument used had been injured and could not 

 be opened more than 64.7 points. The other aperture was then reduced to this size and the value 64. 7 

 was used in place of 100 for a wide-open aperture, and 194 (3 t^mes 64.7) was used in place of 300. The results 

 obtained for the various pulps were sufficiently accurate for comparison with each other. 



