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GLYCOCHOLIC ACID. 419
This extremely delicate test fails, however, when the solution is
heated too high, or if an improper quantity—generally too much—of
the sugar is added. In the last-mentioned case the sugar easily car-
bonizes and the test becomes brown or dark brown. The reaction fails
if the sulphuric acid contains sulphurous acid or the lower oxides of
nitrogen. Many other substances, such as proteins, oleic acid, amyl
alcohol, and morphine, give a similar reaction, and therefore in doubt-
ful cases the spectroscopic examination of the red solution must not be
forgotten. ’<
Pettenkofer’s test for the bile-acids depends essentially on the
fact that furfurol is formed from the sugar by the sulphuric acid (Mylius).
According to Mylius and v. Udranszky ’ a 1 p. m. solution of furfurol
should be used. Dissolve the bile, which must first be decolorized by
animal charcoal, in alcohol. To each cubic centimeter of alcoholic
solution of bile in a test-tube add 1 drop of the furfurol solution and
1 cc. concentrated sulphuric acid, and cool when necessary, so that the
test does not become too warm. This reaction, when performed as
described, will detect -fa to fa milligram cholic acid (v. Udranszky).
Other modifications of Pettenkofer’s test have been proposed.
The reaction with furfurol is not identical with that obtained with
cane-sugar, according to Ville and Derrien, and the absorption-bands
do not occur in the same place in the two cases. The reaction with cane-
sugar does not depend, according to these investigators, upon a furfurol
formation from the sugar. The acid hydrolyzes the sugar, and from the
fructose produced, 4-methyl-2-oxyfurfurol is formed by the further action
of the acid, and this gives the color reaction with the cholic acid. Instead
of furfurol other aldehydes such as vanillin and anisaldehyde can be
used according to Ville and Derrien.2
Glycocholic Acid. The constitution of the glycocholic acid occurring
in human and ox-bile, and which has been most studied, is represented
by the formula C26H43NO6. Glycocholic acid is absent, or nearly so,
in the bile of carnivora. On boiling with acids or alkalies this acid,
which is analogous to hippuric acid, is converted into cholic acid and
glycocoll.
By the action of hydrazine hydrate upon the ethyl ester of cholic acid
Bondi and Muller 3 prepared first cholic-acid hydrazide, and then, by
the action of nitrous acid upon this, they obtained the cholic-acid azide,
C23H39O3CO.N3, and finally from this last in alkaline solution with glyco-
1
Mylius, Zeitschr. f. physiol. Chem., 11; v. Udranszky, ibid., 12.
2
Ville and Derrien, Chem. Centralbl. 1909, 2, 1699 and Compt. rend, eoc, biol. 64
and 66.
3
Zeitschr. f. physiol. Chem., 47.
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