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LACTOSE. 655
Lactose responds to the reactions of glucose, such as Moore’s,1
Trommer’s and Rubner’s, and the bismuth test. It also reduces mer-
curic oxide in alkaline solutions. After warming with phenylhydrazine
acetate it gives on cooling a yellow crystalline precipitate of phenyl
lactosazone, C24H32N4O9. It differs from cane-sugar by giving positive
reactions with Moobe’s or Trommer’s and the bismuth test, and also in
that it does not darken when heated to 100° C with anhydrous oxalic-
acid. It differs from glucose and maltose by its solubility and crystalline
form, but especially, by its not fermenting with yeast, and by yielding
mucie acid with nitric acid.
The osazone obtained with phenylhydrazine acetate, which melts at
200° C, differs from the other osazones by being inactive when 0.2 gram
is dissolved in 4 cc. of pyridine and G cc. of absolute alcohol and viewed
through a layer 10 centimeters long (Xeuberg 2
).
For the preparation of milk-sugar we make use of the by-product
in the preparation of cheese, the sweet whey. The protein is removed
by coagulation with heat, and the filtrate evaporated to a syrup. The
crystals which separate after a certain time are recrystallized from water
after decolorizing with animal charcoal. A pure preparation may be
obtained from the commercial milk-sugar by repeated recrystallization.
The quantitative estimation of milk-sugar may be performed either by
the polaristrobometer or by means of titration with Fehling’s solution.
Ten cc. of Fehling’s solution are reduced by 0.0G7G gram of milk-sugar
in 0.5-1.5 per cent solution after boiling for six minutes. (In regard to
Fehling’s solution and the titration of sugar see larger hand-books.)
From the non-correspondence between the quantity of sugar in the
milk as determined by polarization and gravimetrically, when the polar-
ization results are always higher, Sebelien 3
has concluded that the
milk must contain a second reducing substance which polarizes stronger
than lactose. This substance is probably a pentose and occurs to a very
slight extent in ordinary milk, 0.25-0.3") p. m. (Sebelien and Sunde),
and more in colostrum, 0.5 p. m.
Ritthausen found another carbohydrate in milk which is soluble in water,
non-crystallizable, which has a faint reducing action, and which yields, on boiling
with an acid, a body having a greater reducing power. Becha.mp 4
considers
this as dextrin.
1
The well-known beautiful red color, which milk produces after the addition of
alkali, at the room temperature and to which attention has been called recently by
Gautier, Morel, and Monod (Compt. rend. soc. biol., 60 and C»2), and Kriiger (Zeitschr.
f. Physiol. Chem., 50) is a Moore’s reaction modified by the presence of protein and
perhaps also other milk constituents.
2
Ber. (1. d. Chem. Gesellsch., 32.
’Sebelien, Hammarsten’s Festschrift, 1906; with Sunde, Zeitschr. f. angew.
Chem., 21.
4
Ritthausen, Journ. f. prakt. Chem. (N. F.), 15; Beehamp, Bull. Soc. Chim. (3), 6.
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