46 BULLETIN 1187, U. S. DEPARTMENT OF AGRICULTURE. 
tinted hydrochloric acid, and let stand overnight for inversion. 
(Standing 48 hours does not apparently affect the results.) Then pour 
the inverted solution into a 400 cubic centimeter beaker and neutralize 
with anhydrous sodium carbonate; return it to the 100 cubic centi- 
meter flask and make up to the mark. Filter, if necessary, and use 
50 cubic centimeters for the determination of total sugars as invert, 
as directed above. 
The amount of copper obtained in either the reducing or the total 
sugar determinations represents the sugar contained in 2 grams of 
the material. Therefore the weights of the invert sugar when divided 
by 2 and multiplied by 100 give the respective percentages of sugar 
as invert. Subtract the percentage of reducing sugars before inver- 
sion from the percentages of total sugar after inversion, both calculated 
as invert, and the difference multiplied by 0.95 gives the percentage 
of sucrose. Since the insoluble matter of the material to be analyzed 
occupies some space in the flask as originally made up, it is necessary 
to correct for this volume. Results of a large number of determina- 
tions on various materials have shown the average volume of 12 grams 
of material to be 9 cubic centimeters; therefore the correction factor 
for 12 grams in 300 cubic centimeters is 0.97 and the percentage 
figures for reducing sugar and sucrose are to be multiplied by this 
factor to obtain the true amounts. 21 
The number of milligrams of copper reduced by a given amount of 
reducing sugar differs when sucrose is present and when it is absent. 
In the tables the absence of sucrose is assumed, except in the two 
columns under invert sugar, where one for mixtures of invert sugar 
and sucrose containing 0.4 gram of total sugar in 50 cubic centimeters 
of solution, and one for invert sugar and sucrose when the 50 cubic 
centimeters of solution contains 2 grams of total sugar are given, in 
addition to the column for invert sugar alone. 
STARCH-DIASTASE METHOD WITH SUBSEQUENT ACID HYDROLYSIS. 22 
Reagents. — Malt Extract. — Digest 10 grams of fresh, finely ground malt with 200 
cubic centimeters of water for 2 or 3 hours at ordinary temperature and filter. Deter- 
mine the amount of dextrose in a given quantity of the filtrate after boiling with acid, 
etc., as in the starch determination, and make the proper correction in the subsequent 
determination. 
Determination. — Extract 5 grams of the substance (ground to 
an impalpable powder and representing 4 or 5 grams of the dry 
material) on a hardened filter with 5 successive portions of 10 cubic 
centimeters of ether; wash with 150 cubic centimeters of 50 per cent 
alcohol (10 per cent alcohol has not been found satisfactory, because 
it will extract some soluble starch). Place the residue in a beaker 
with 50 cubic centimeters of water, immerse the beaker in boiling 
water, and stir constantly for 15 minutes or until all the starch is 
gelatinized; cool to 55° C, add 20 cubic centimeters of malt extract 
and heat gradually for an hour, raising the temperature to 72° C. in 
this time. Heat again to boiling for a few minutes, cool to 55° C, 
add 20 cubic centimeters of malt extract and maintain at this tem- 
perature for an hour or until the residue treated with iodin shows no 
blue color upon microscopic examination. Cool, make up directly to 
21 U. S. Department of Agriculture, Bureau of Chemistry Circular 71, Extraction of Grains and Cattle 
Foods for the Determination of Sugars, by A. H. Bryan, A. Given, and M. N. Straughn, p. 3, 1911. 
22 Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists. Re- 
vised to November 1, 1919, p. 95, par. 60 and 61. 
