22 BULLETIN 620, U. S. DEPARTMENT OF AGRICULTURE. 
METHODS OF ANALYSIS AND OTHER TESTS. 
BONE-DRY WEIGHT. 
The bone-dry weight was determined by taking a sample of the 
wood, pulp, or screenings and drying to constant weight in an oven 
at 104° ©. The ratio of the weight after drying to that before drying 
then became the factor by which the bone-dry weight of the entire 
amount was calculated. All yields and similar calculations are made 
on the basis of bone-dry weight. 
COLOR. 
The color of the pulp was determined by means of the Ives tint 
photometer. By means of this apparatus the color of the paper is 
reduced into parts of the three primary colors, red, green, and blue. 
When these three add up to 300, as in the case of the magnesia 
standard used for comparison, then pure white is obtained. The 
sum of the three primary colors subtracted from 300 gives the 
‘“‘narts black” of the paper in question and is a measure of its color, 
the higher the parts black, the darker the pulp. 
BLEACH REQUIRED. 
The bleaching solution was made by mixing bleaching powder 
with water, allowing the sediment to settle and drawing off the clear 
solution. Its strength was determined by titrating 10 cc with aes 
solution of sodium arsenite using starch iodide paper as an outside 
indicator. The number of cubic centimeters necessary to complete 
the titration gives the gram per liter of 35 per cent bleach. Twenty- 
five grams (bone-dry) of the pulp were put in enameled jars with 
2,000 cc of water and thoroughly mixed. The calculated amount 
of bleach liquor was then added and jars placed in a water bath 
heated with an electric coil which kept it a temperature of 110° F. 
The contents of the jar were kept in motion by means of a stirring 
apparatus until all the bleach was exhausted. The pulp was then 
thoroughly washed, made into hand sheets, and its color compared 
with a standard to which the addition of more bleach would not 
make it any whiter. The per cent of bleach necessary to give a 
standard white is expressed in per cent of the bone-dry weight of the 
owe ANALYSIS OF COOKING LIQUOR.— 
PREPARATION OF |x IODINE. 
The iodine solution is made by diluting from a concentrated solu- 
tion. This was made by dissolving 156.7 grams of iodine and 217 
grams of potassium iodide in about 250 cc of water and diluting to 1 
