2 BULLETIN 102, U. S. DEPARTMENT OF AGRICULTURE. 



meyer flask, then add 50 c. c. of 80 per cent alcohol, specific gravity 

 0.86, and stop the flask tight with a cork or rubber stopper. In 

 order that the meal may be thoroughly and equally subjected to the 

 action of the alcohol, carefully shake the flask with a whirling motion, 

 avoiding a distribution of the meal on the sides of the flask. After 

 shaking, let the meal digest in the alcohol over night (approximately 

 16 to 18 hours). After digestion filter through a dry filter paper. 

 Place 25 c. c. of the clear filtrate in a 250 c. c. beaker and add 75 

 c. c. of distilled water and 1 c. c. of phenolphthalein solution and 

 titrate with a one-hundredth normal alkali solution. The proteids 

 dissolved in the alcohol are thrown out of solution when water is 

 added, leaving a white precipitate, which makes it difficult to deter- 

 mine just what constitutes an end point in the titration. The end 

 point that has been adopted is perhaps a slight degree over the point 

 of neutrality, but it is necessary to carry the titration to a distinct 

 color in order to get comparable results. This titration, as will be 

 readily seen when making the determination, is different from most 

 titrations, owing to the cloudy white precipitate formed on the addi- 

 tion of water to the alcoholic extract, which in a measure obscures 

 the color. It will, however, be necessary to analyze corn ranging in 

 color from pure white to deep yellow, where in each case the color of 

 the extract is slightly different. One also has to deal with mixtures 

 of white and yellow corn, where again another colored extract results, 

 depending upon the relative quantity of white and yellow corn pres- 

 ent in the sample. Plate I will help persons who perform this analysis 

 for the first time to get the correct color. The colors shown repre- 

 sent titrations of yellow, mixed, and white corn, and it will be seen 

 that the color of the liquid obtained at the end point is slightly 

 different in each of the three cases. It is not expected that persons 

 making this test shall match these colors exactly, but they are 

 intended to give one as clear an idea of the color as can be shown on 

 paper. 



To correct the reading of the burette for the acid contained in the 

 alcohol and phenolphthalein, make a blank by taking 25 c. c. of 

 alcohol, 75 c. c. of distilled water, and 1 c. c. of phenolphthalein 

 solution and titrate in the same manner as the corn extract. Sub- 

 tract the reading thus obtained from the reading obtained by titrating 

 the corn extract, and the result will represent the true acidity in 5 

 grams of corn. Multiply this result by 2, and it will represent the 

 number of cubic centimeters of one-hundredth normal alkali required 

 to neutralize the acid in 10 grams of corn, or the number of cubic 

 centimeters of normal alkali required to neutralize the acid in 1,000 

 grams of corn. This result is termed the "degree of acidity" of the 

 corn. 



