Jan. 6. 19X9 Determination of Acidity and Nitrogen in Wheat 3 



PERIODS OF TIME AND TEMPERATURES USED 



After some preliminary work the following periods were chosen: 5, 30, 

 and 60 minutes, 2, 4, 8, 16, and 24 hours. Extractions were made at the 

 following temperatures: 5°, 20°, 40°, and 50° C. Other temperatures 

 and periods were tried in the preliminary work, but the results obtained 

 were found of no added value. 



METHOD OF DETERMINING THE HYDROGEN-ION CONCENTRATION 



One hundred cc. of the solution prepared as above — namely, the extract 

 of 10 gm. of ground wheat — were pipetted into the hydrogen-ion cell. 

 This is closed with a rubber stopper through which the electrodes, as well 

 as the tip of the burette, are inserted. In this way the carbon dioxid 

 from the air is excluded. The hydrogen gas is bubbled through until 

 equilibrium is reached. The reading of the voltmeter gives the figure 

 for calculating the actual hydrogen-ion concentration of the solution. 

 To facilitate this calculation, we have made a table giving the hydrogen- 

 ion concentration corresponding to the volt readings from 0.281 to 1.090. 

 It takes about an hour to obtain equilibrium, but this can be shortened 

 by previously saturating the electrode with hydrogen. 



Barium hydroxid {N/20) was then added till the solution showed a volt 

 reading of 0.686, indicating a hydrogen-ion concentration of Pg 7. This 

 represents the absolute neutral point. The alkali was again added till 

 the volt reading was 0.760, indicating a ?□ value of 8.3. This corresponds 

 to the acidity as commonly determined by the use of phenolphthaiein as 

 indicator. In several trials this indicator was added at this point, and 

 gave the usual color change. The alkali was again added until the volt 

 reading was 0.820, indicating a Pq value of 9.3. This is the point of color 

 change of thymolphthalein, and this was actually determined by the 

 use of the indicator. At this point 25 cc. of formaldehyde solution were 

 added. This was made by mixing one part of 40 per cent formaldehyde 

 with two parts of carbon-dioxid-free water and neutralizing to the hydro- 

 gen-ion value Ph 9-3 before using. The hydrogen gas was bubbled 

 through until equilibrium was reached, and the Pg value noted. Barium 

 hydroxid {N/20) was then added until a Pg value of 9.3 was again reached. 



HYDROGEN-ION CONCENTRATION OF WHEAT EXTRACT 



The results obtained by these methods at temperatures varying from 

 5° to 50° C, and for periods varying from 5 minutes to 24 hours are given 

 in Table I. 



