NA EE A Ta 
16,6 Quisumbing: Determination of Glucose and Starch 595 
sible amount of methyl alcohol and the solution thus obtained 
was treated with a few cubic centimeters of ether until crys- 
tals began to appear. The vessel was then placed in a desicca- 
tor over concentrated sulphuric acid and the alcohol allowed to 
evaporate slowly. The crystals were separated from the mother 
liquor by suction and washed with small amounts of methy! 
alcohol and ether, and then dried at 40° C. under vacuum in 
an apparatus similar to that described in Browne’s Handbook 
of Sugar Analysis, page 23. 
D. APPLICATION OF THE METHOD TO STARCH ANALYSIS 
DIRECT ACID HYDROLYSIS (MODIFIED TO SUIT CONDITIONS FOR OXIDATION WITH 
POTASSIUM PERMANGANATE), APPLICABLE TO GLUCOSE 
AND COMMERCIAL STARCH 
Stir a 2- to 3-gram sample of the dry material in a beaker 
with 50 cubic centimeters of cold water for an hour. Transfer 
to a filter and wash with 250 cubic centimeters of cold water. 
Heat the insoluble residue for from three to four hours with 
200 cubic centimeters of water and 15 cubic centimeters of sul- 
phuric acid (specific gravity, 1.84) in a flask provided with a 
reflux condenser. Cool and neutralize exactly with sodium hy- 
droxide solution. Complete the volume to 500 cubic centime- 
ters, filter, and determine the dextrose in an aliquot of the fil- 
trate as directed under the described method of procedure. 
The number of milligrams of dextrose, or its equivalent in starch 
in solution, corresponding to the number of cubic centimeters 
of 0.1 N potassium permanganate used by the samples, will be 
given by the corresponding values in Table 5, by interpolation 
if necessary. 
The factor 0.9 is the theoretical ratio between starch and 
glucose but, according to Noyes(11) and other investigators, the 
factor 0.93 more nearly approaches the actual value. The 
factor 0.93 is used in this work. 
THE SALIVA METHOD,(7) APPLICABLE TO ALL PRODUCTS CONTAINING STARCH 
The direct acid hydrolysis method just described cannot be 
applied to the analysis of flour or other plant products contain- 
ing substances other than starch, as will be seen in Table 6. 
If, however, the diastase or saliva method is used, results that 
are comparable with those by the Munson and Walker method 
are obtained. 
Saliva contains the ferment ptyalin, which possesses the 
power of bringing starch into solution by converting it into 
dextrin and finally into maltose. 
