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432 THE LIVER.
from bilirubin by oxidation under special conditions (Kuster). A green
coloring-matter similar in appearance is formed by the action of other
reagents such as CI, Br, and I. According to Jolles,1
,
biliverdin is
produced by the use of Hubl’s iodine solution, while according to others
(Thudichum, Malt 2
) substitution products of bilirubin are formed.
Gmelin’s Reaction for Bile-pigments. If one carefully pours nitric
acid, containing some nitrous acid, under an aqueous solution of alkali
bilirubin, there is obtained a series of colored layers at the juncture of the
two liquids in the following order from above downward: Green, blue,
violet, red, and reddish-yellow. This color reaction, Gmelin’s test,
is very delicate, and serves to detect the presence of one part bilirubin
in 80,000 parts liquid. The green ring must never be absent; and also the
reddish-violet must be present at the same time, otherwise the reaction
may be confused with that for lutein, which gives a blue or greenish ring.
The nitric acid must not contain too much nitrous acid, for then the reac-
tion takes place too quickly and it does not become typical. Alcohol
must not be present in the liquid, because, as is well known, it gives a
play of colors, in green or blue, with the acid.
Hammarsten’s Reaction. An acid is first prepared consisting of 1
vol. nitric acid and 19 vols, hydrochloric acid (each acid being about
25 per cent). One volume of this acid mixture, which can be kept for
at least a year, is, when it has become yellow by standing, mixed with
4 vols, alcohol. If a drop of bilirubin solution is added to a few cubic
centimeters of this colorless mixture a permanent beautiful green color
is obtained immediately. On the further addition of the acid mixture
to the green liquid all the colors of Gmelin’s scale, as far as choletelin,
can be produced consecutively.
Huppert’s Reaction. If a solution of alkali bilirubin is treated with
milk of lime or with calcium chloride and ammonia, a precipitate is
produced consisting of calcium bilirubin. If this moist precipitate, which
has been washed with water, is placed in a test-tube and the tube half
filled with alcohol which has been acidified with hydrochloric acid, and
heated to boiling for some time, the liquid becomes emerald-green or
bluish-green in color.
In regard to the modifications of Gmelin’s test and certain other
reactions for bile-pigments, see Chapter XIV (Urine).
That the characteristic play of colors in Gmelin’s test is the result
of an oxidation is generally admitted. The first oxidation step is the
1
Kuster, Ber. d. d. chem. Gesellsch., 35 and 59; Jolles, Journ. f .prakt. Chem. (N.F.),
59, and Pfluger’s Arch., 75.
2
Thudichum, Journ. of Chem. Soc. (2),’ 13, and Journ. f. prakt. Chem. (N.F.),
53; Maly, Wien. Sitzungsber., 72.
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