22 BULLETIN 620, IT. 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° C. 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 

 ''parts 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 



0.987N 

 solution. Its strength was determined by titrating 10 cc with — ttj — 



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 



pulp. 



ANALYSIS OF COOKING LIQUOR. 



PREPARATION OF jg 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 



