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. 
0,04 0.2 04 06 08 
T T 
o) es ee 
tl wees a 
is 2 a at 
ee ee ee | 
= of [ett BSC CEP RNL 
vd i | a OM A 
= fia wee 
j a | | 
Ss | | r | | Nba | 
g 2° i I~ | Nez [ 
= oe ee ee 
a IS sae Bee Gee 
§ | | 
fe 
~— f | 
eZ i 
ee ee ee —$——4 
= T 
/ | / 
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 50 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 
STANDARDIZATION 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 
