XV] CEREAL FOODS 191 



keeping the temperature of the liquid in the flask at 40°C. and shaking at 10 minute 

 intervals. Finally filter on a dry, nitrite-free, folded filter. Return the first run- 

 nings 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 2 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 loos- 

 ened 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 fun- 

 nel covered with a watch glass to prevent evaporation. In order to secure a clear 

 filtrate, a certain quantit}^ of the flour should be allowed to pass over onto the paper 

 and the first portion of the filtrate passed through a second time. It will be found 

 convenient to fit the filter paper to the funnel by means of water and dry thoroughly 

 either by standing overnight in a well-ventilated place or by heating. 



Determine the color value of the clear gasoline solution in a Schreiner or similar 

 colorimeter, using for comparison a 0.005% potassium chromate solution. This solu- 

 tion corresponds to a gasoline number of 1.0 and is conveniently prepared by dilu- 

 ting 10 cc. of a 0.5% solution to 1 liter. The colorimeter tube, containing the 

 gasoline solution, should first be adjusted so as to read 50 mm., then the tube 

 containing the standard chromate solution raised or lowered until the shades of yellow 

 in both tubes match. The reading of the chromate solution, divided by the reading 

 of the gasoline solution, gives the gasoline color value. The color value may be deter- 

 mined also in Nessler tubes, using for comparison potassium chromate solutions 

 of various dilutions prepared from a 0.5% solution and filling the tubes in all cases 

 to the height of 50 mm. 



BIBLIOGRAPHY. 



» U. S. Bur. Chem. Bull. 152, p. 104. 

 * Ibid., 81, p. 124. 

 » Ibid., 122, p. 54. 



