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224 THE CARBOHYDRATES.
hydrolytic cleavage of complex carbohydrates. Isomaltose is also obtained
from glucose by reversion (see page 225).
The disaccharides or hexobioses are to be considered as glucosides,
each of which is derived from two monosaccharides with the exit of 1
molecule of water. Corresponding to this, their general formula is
C12H22O11. On hydrolytic cleavage and the addition of water they
yield 2 molecules of hexoses, either 2 molecules of the same hexose or
one each of two different hexoses. Thus
Saccharose -j- H2O = glucose +fructose
;
Maltose -f- H2O = glucose +glucose
;
Lactose +H2O = glucose +galactose.
The configuration of the disaccharides has not been positively determined.
The fructose turns the polarized ray more to the left than the glucose
does to the right; hence the mixture of hexoses obtained on the cleavage
of saccharose has an opposite rotation to the saccharose itself. On
this account the mixture is called invert-sugar, and the hydrolytic
splitting is designated as inversion. This term, "inversion," is not only
used for the splitting of saccharose, but is also used for the hydrolytic
cleavage of compound sugars into monosaccharides. The reverse reaction,
whereby monosaccharides are condensed into complex carbohydrates, is
called reversion.
We subdivide the disaccharides into two groups, first, the group to
which saccharose belongs, where the members do not have the property
of reducing certain metallic oxides; and the second group, to which the
two maltoses and lactose belong, the members acting like monosaccharides
in regard to the ordinary reduction tests. The members of the latter
group have the character of aldehyde alcohols, and in milk-sugar the
aldehyde characteristics are connected with the glucose fraction.
Saccharose, or cane-sugar, occurs extensively distributed in the
plant kingdom. It occurs to the greatest extent in the stalk of the sugar-
millet and sugar-cane, the roots of the sugar-beet, the trunks of certain
varieties of palms and maples, in carrots, etc. Cane-sugar is of extraor-
dinary great importance as a food and condiment.
Saccharose forms large, colorless monoclinic crystals. On heating it
melts in the neighborhood of 160° C, and on heating more strongly it
turns brown, forming so-called caramel. It dissolves very readily in
water, and according to Herzfeld,1
100 parts of saturated saccharose
solution contain 67 parts of sugar at 20° C. It dissolves with difficulty
in strong alcohol. Cane-sugar is strongly dextrorotatory. The specific
rotation is only slightly modified by concentration, but is markedly
1
See Tollens’ Handbuch der Kohlehydrate, 2. Aufl. 1, 154.
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