Oct. 1, 1919 Method for Measuring Acidity of Cereal Products 



43 



employed only the ice-water method, and not the alcohol method, when 

 first examining these com meals. From the figures obtained by Mr. 

 Mastin it is also clear that by extracting samples 53 to 55 with alcohol 

 in the manner prescribed by Besley and Baston, it was not possible to 

 bring into solution all of the acid-reacting constituents of these meals. 



FURTHER STUDY OF THE ICE-WATER EXTRACTION METHOD 



The following experiments were carried out by me for the purpose of 

 studying more closely the conditions and limitations of the ice-water 

 extraction method. 



It was thought that a brief boiling might possibly give some indication 

 of the character of the free acids present in ice-water extractions of oats 

 and corn. Equal aliquots of filtered ice-water extracts were therefore 

 pipetted into Erlenmeyer flasks and the one sample heated to boiling on 

 an asbestos screen, while the other was titrated directly. The boiling 

 was continued for 30 seconds, whereupon the flask was removed from the 

 screen, cooled under the tap, and at once titrated. 



Table III. — Effect of heating upon the acidity of ice-water extractions of oats and corn ^ 



Sample No. 



Titrated after 

 boiling ]/i 

 minute. 



Unsulphured oats: 



58 



59 



Sulphured oats: 

 58s 



^ 59s 



Com meals: 



60 



61 



' Expressed in cubic centimeters of normal alkali required to neutralize the extract from i.ooo gm. of 

 material. 



It is seen from the foregoing table that the short heating had no appre- 

 ciable influence on the titration values of these samples. The boiled 

 liquids, moreover, showed no precipitate or other visible changes. Upon 

 standing in the cold-storage room over night both the boiled and the un- 

 boiled extracts had turned acid again. It may be mentioned that I have 

 regularly observed that ice- water extractions of oats or corn when filtered 

 and kept at a temperature of 1° to 2° C. for over a day without being 

 neutralized show no change in acidity. However, if such extracts are 

 neutralized they form fresh acid upon standing and continue to do so 

 after renewed neutralization. The presence of chloroform does not afi"ect 

 this acid formation. Apparently, therefore, the acidity found in each of 

 these extracts represents a chemical equilibrium, which tends to become 

 reestablished if disturbed by the process of neutralization. 



