16,6 Quisumbing: Determination of Glucose and Starch 597 
Weight of cuprous oxide. 
Samples. 
Grams. 
Blanks. 
Grams. 
0.1125 
0.1141 
0.1136 
0.1134 
0.0015 
0.0017 
0.0016 
0.4536 
Average, 0.1135 
0.0048 
0.0016 
Total weight of cuprous oxide from 10 cubic centimeters of glucose 
solution, 111.9 milligrams. ^ 
111.9 milligrams cuprous oxide, 48.6 milligrams glucose. 
Glucose found by analysis, 99.20 per cent. 
ANALYSIS OF PURE GLUCOSE, BY THE ALKALINE POTASSIUM PERMANGANATE 
METHOD 
Sample 1. — 0.100 gram of glucose was dissolved in 100 cubic centi- 
meters of distilled water, and 10 cubic centimeter portions were taken 
for analysis. 
Ten milligrams of glucose required 12.34 cubic centimeters of 0.1 N 
potassium permanganate solution. 
12.34 cubic centimeters of 0.1 N potassium permanganate according 
to values in Table 5 are equivalent to 10.02 milligrams of glucose. 
Glucose found by analysis, 100.2 per cent. 
Sample 2. — ^0.500 gram of glucose was dissolved in 100 cubic centi- 
meters of distilled water, and 5 cubic centimeter portions were taken for 
analysis. 
25 milligrams of glucose required 29.24 cubic centimeters 0.1 N potas- 
sium permanganate solution. 
29.24 cubic centimeters 0.1 K! potassium permanganate according to 
values in Table 5 are equivalent to 24.76 milligrams dextrose. 
Glucose found by analysis, 99.04 per cent. 
Table 6 shows that the alkaline potassium permanganate used 
with the direct acid hydrolysis method for the determination of 
starch in flour gives results that are about 10 per cent higher 
than those obtained with the Munson and Walker method. 
This is undoubtedly due to oxidation of soluble substances pres- 
ent in the flour. With commercial starch preparation, the 
results by the two methods differ by 0.65 per cent, although 
at times the difference may reach 1 per cent. The determina- 
tion of flour by hydrolosis with saliva gives results by the two 
methods which agree very closely. 
The extent to which glucose is oxidized by constant concentra- 
tion of potassium permanganate varies for the same concentra- 
tion of glucose with change in the concentration of alkali. In 
the case of a mixture of 25 cubic centimeters of 0.2 N potassium 
SUMMARY 
