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GLUCOSE. 213
(levulose), in honey, sweet fruits, seeds, roots, etc. It occurs in the
human and animal intestinal tract during digestion, also in small quan-
tities in the blood and lymph, and as traces in other animal fluids and
tissues. It occurs only as traces in urine under normal conditions,
while in diabetes the quantity is very large. It is formed in the hydro-
lytic cleavage of starch, dextrin, and other compound carbohydrates,
as also in the splitting of glucosides. The question whether glucose
can be formed in the body from proteins or from fats is disputed and will
be discussed in a following chapter (VII).
Properties of Glucose. Glucose crystallizes sometimes with 1 mole-
cule of water of crystallization in warty masses consisting of small leaves
or plates, and sometimes when free from water in fine needles or prisms.
The sugar containing water of crystallization melts even below 100° C.
and loses its water of crystallization at 110° C. The anhydrous sugar
melts at 146° C, and is converted into glucosan, CeHioOs, at 170° C.
with the elimination of water. On strongly heating it is converted into
caramel and then decomposes.
Glucose is readily soluble in water. This solution, which is not as
sweet as a cane-sugar solution of the same strength, is dextrogyrate and
shows strong birotation. The specific rotation is dependent upon the
concentration of the solution, as it increases with an increase in the con-
centration. A 10 per cent solution of anhydrous glucose can be taken as
+52.5° at 20° C.1
Glucose dissolves sparingly in cold, but more freely
in boiling alcohol. One hundred parts alcohol of sp. gr. 0.837 dissolves
1.95 parts anhydrous glucose at 17.5° C. and 27.7 parts at the boiling
temperature (Anthon2
). Glucose is insoluble in ether.
If an alcoholic caustic-potash solution is added to an alcoholic solu-
tion of glucose, an amorphous precipitate of insoluble sugar-potash
compound is formed. On warming this compound it decomposes easily
with the formation of a yellow or brownish color, which is the basis of
Moore’s test. Glucose also forms compounds with lime and baryta.
Moore’s Test. If a glucose solution is treated with about one
quarter of its volume of caustic potash or soda and warmed, the solution
becomes first yellow, then orange, yellowish-brown, and lastly dark
brown. It has at the same time a faint odor of caramel, and this odor
is more pronounced on acidifiying.3
Glucose forms several crystallizable combinations with NaCl of
which the easiest to obtain is (CeHioOG^-NaCl-fH^O, which forms
1
For further information see Tollens’ Handbuch der Kohlehydrate, 2. AuflL, 44.
2
Cited from Tollens’ Handbuch.
3
In regard to the products formed in this reaction, see Framm, Pfluger’s Arch., 64;
Neff, Annal. d. Chem. u. Pharm., 357; Buchner and Meisenheimer, Ber. d. d. chem.
Gesellsch., 39; Meisenheimer, ibid., 41.
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