FEEDS

163

judged by the color of the solution, remove about 1 cc of the liquid and
filter rapidly into a small porcelain crucible or on a test plate; acidify with
10-per cent acetic acid and test for copper with a 5-per cent, potassium
ferrocyanide solution. After the end point has been reached calculate the
invert sugar equivalent of the cupric sulphate solution.

Determine the reducing sugars of the solution containing the extract from
the feed by adding it to the Fehling's solution in the manner described for
the standard invert sugar solution. In this case the approximate sugar
content is not known and the first trial may show that too much was added.
If so, make another trial, modifying the volume of sugar solution to be added.

Calculate the weight of reducing sugar as dextrose which, of course, has

the same equivalent weight as does invert sugar. Multiply by----—

( = 0.964 X 2QQ X -—j, where v — volume of sugar solution used, and

calculate the per cent in the original 12 gm of sample.

Determination of Sucrose.—Pipette 25 cc of the clarified sugar solution
from the feed sample (page 159) into a 100-cc volumetric flask, add a few
drops of methyl orange, neutralize with dilute hydrochloric acid and then
add 5 cc of concentrated hydrochloric acid and allow the inversion to
proceed at 20° for 24 hours. Neutralize with sodium carbonate, then
dilute to the mark with water, filter if necessary and determine reducing
sugars in 50 cc of the solution by any of the methods described for reducing

sugars. Multiply by 9.64 (=0.964 X 200 X ^ Xljo") to obtain the

weight of sugar in the original 12 gm of sample. Calculate the per cent.
Subtract the per cent of reducing sugars before inversion from the percent

of total reducing sugar after inversion, both being calculated as invert sugar,

.. -~, — _ .

= 0.95 I to obtain

360

(C H O
o/S" TJ22 rT^
JOeH^Oe

the per cent of sucrose.

Starch: Diastase Hydrolysis.—When starch is gelatinized
by boiling with water it is possible to convert it to maltose and
dextrin by treating it with either ptyalin or malt diastase, these
enzymes accelerating the hydrolysis:

(CeHioOs)^ + ^EUO —-> — Ci2H220n.

(Taka-diastase,1 if available, is more convenient to use, no
blank determination being required with malt extract.) The
enzymes thus introduced have no action on other carbohydrates
present. Starches from the different grains are not acted upon
with equal vigor by diastase so it is necessary to test with iodine
solution to determine whether the conversion has been completed.
iJ.Agr. Sci., 11, 9 (1921).

I