Official methods of analysis of the Association of Official Analytical Chemists Volume 1 - Tapa blanda

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ...to the flour being minimized by the white background. The solutions should be allowed to subside and should not be shaken during comparison; or, (2) Weigh 20 grams of the flour into a 500 cc. Erienmeyer flask, add 200 cc. of nitritefree water, previously warmed to 40C, and close the flask with a rubber stopper. Shake vigorously for 5 minutes and digest for an hour in a water bath, keeping the temperature of the liquid in the flask at 40C. and shaking at 10 minute intervals. Finally filter on a dry, nitrite-free, folded filter. Return the first runnings to the filter until a clear filtrate is obtained. Pipette 50 cc. of the filtrate and 50 cc. of the standard nitrite solution into small flasks; add to each, 50 cc. of water, 2 cc. each of the sulphanilic acid and alpha-naphthylamin hydrochlorid solutions, shake and allow to stand an hour to bring out the color. Compare the two solutions in a colorimeter. Divide the height of the column of the standard solution by that of the solution of the sample, to obtain the parts of nitrogen as nitrous acid (free and combined) per million of flour. 21 GASOLINE COLOR VALUE.--TENTATIVE. Place 20 grams of the flour in a wide-mouthed, glass-stoppered 120 cc. bottle and add 100 cc. of colorless gasoline. Stopper tightly and shake vigorously for 5 minutes. After standing 16 hours, shake again for a few seconds until the flour has been loosened from the bottom of the bottle and thoroughly mixed with the gasoline, then filter immediately on a dry 11 cm. paper into an Erlenmeyer flask, keeping the funnel covered with a watch glass to prevent evaporation. In order to secure a clear filtrate, a certain quantity of the flour should be allowed to pass over onto the paper and the first portion of the filtrate passed through a second t...