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 
i 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 times 64.7) was used in place of 300. The results 
obtained for the various pulps were sufficiently accurate for comparison with each other. 
