136

QUANTITATIVE AGRICULTURAL ANALYSIS

& N •/

•' I

•tl

,$

1 Sii

Iii these formulas the symbols have the significance expressed
in the Clerget formula.

Beet Products. — The interference of raffinose in the calcula-
tion of sucrose from direct and invert polarizations has already
been noted. If the direct polarization reads more than 1° I.
higher than the sucrose calculated as already described, the
presence of raffinose is indicated. In this case sucrose and
raffinose are calculated by the formula of Herzfeld:

S =

R =

0.839
P -S
1.852'

(7)
(8)

R indicating the per cent of raffinose and the other symbols
having their former significance.

Commercial Glucose.—This substance contains dextrin and
maltose in variable quantities, in addition to the essential
dextrose. The specific rotation of the various dextrines is
usually about +193 and that of maltose is about +138, that of
dextrose being only +53. On this account the specific rotation
of commercial glucose is somewhat variable but it is always
higher than that of dextrose. The investigations of Leach1
indicate that +175° I. is the average rotation for a solution con-
taining 26 gm of commercial glucose in 100 cc polarized in a 200-
mm tube. From this is deduced the formula:

100(a - S)

Cf =

175

(9)

a indicating the direct polarization in International degrees, S the
per cent of sucrose, determined as already directed, and G the per
cent of commercial glucose polarizing +175° I. If invert sugar
is present the formula is inapplicable. In this case use is made of
the fact that the left rotation of invert sugar decreases with
rising temperature, becoming zero at 87° C. At this tempera-
ture the mean rotation of commercial glucose has dropped
to +163° L, so that the calculation is made by the formula:

ao>

where / is the corrected invert reading at 87° C.
1 U. S. Dept. of Agr. Chem. Bull 65, 48.

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