16,6 Quisumbing : Determination of Glucose and Starch 587 
1. The selection of a concentration which would be least likely 
to oxidize soluble substances. 0.1 N potassium permanganate 
was chosen, in preference to either the 0.2 N or the 0.05 N, be- 
cause it was thought that this concentration would have less 
chance than would the 0.2 N to oxidize soluble substances other 
than glucose that might be present in the commercial product, 
and at the same time would give more accurate results; while, 
on the other hand, it would give a greater range of glucose 
concentration than the 0.05 N. 
2. The selection of a concentration of alkali which would give 
a wider range of concentration of glucose consistent with uni- 
Normality of alkali. 
0,Z OA- 06 0.8 
r 
5i 
i. 
1 
t::: 
s 
3 i 
7 
! 
p 
\ 
[7 
k 
>3 
\ 
V 
i 
i 
I 
1 
1 
1 
. — ( 
k 
1 
7 
Fig. 2. Effect of normality of alkali on the amount of potassium permanganate in cubic 
centimeters of 0.1 N solution reduced to glucose. Curves 1, 2, 3, 4, and 5 are for 10, 20, 
30, 40, and 60 milligrams, respectively. 
formity of results; 0.04 N, as shown by the uniform slope of 
its curve, fulfills this condition. 
B. DETERMINATION OF THE OPTIMUM TEMPERATURE AND TIME OF 
HEATING 
STANDAEDIZATION OF HEATING POWER 
Mechanical arrangement. — The solution is heated in a 400 
cubic centimeter Erlenmeyer flask, closed with a two-hole rub- 
ber stopper; one hole holds the thermometer, the other an exit 
tube for the steam. The flask is placed on an asbestos wire 
gauze over a tripod, and the flame so regulated that it will heat 
60 or 100 cubic centimeters of water from 29° to 95° C. in 
approximately two or four minutes, as the case may be. Draught 
171585 4 
