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194 THE PROTEIN SUBSTANCES.
and Johnson l
have also prepared it synthetically. It is transformed
into uracil by the action of nitrous acid.
The free base is soluble with difficulty in water {129 parts) and crystal-
lizes in thin leaves with a mother-of-pearl luster. It is insoluble in ether
and soluble with difficulty in alcohol. The double compound with platinum
chloride, the crystalline picrate, the nitrate, and the picrolonate are
of importance in the detection of cytosine. This base is precipitated
by phosphotungstic acid and by silver nitrate in the presence of an
excess of barium hydroxide, which fact is of importance in the detection
of cytosine (Kutscher). The double bismuth-potassium iodide gives
a brick-red precipitate. Cytosine gives the murexid reaction with
chlorine-water and ammonia (see Chapter XIV), and also the reaction
described by Wheeler and Johnson under uracil. In regard to
preDaration see Kossel and Steudel 2
and also Kutscher.3
HN—CO
Uracil, C4H4N202, = OC CH (2, 6 - dioxypyrimidine) , was first
HN—CH
obtained by Ascoli and Kossel from yeast nucleic acid and later from
various complex nucleic acids, perhaps secondarily from the cytosine as a
cleavage product. The synthetical preparation was first accomplished by
E. Fischer and Roeder.4
Uracil crystallizes in needles which cluster in rosettes. On careful
heating it sublimes in part undecomposed, but develops red vapors and
decomposes in part. It is readily soluble in hot water, but less so in cold
water, and nearly insoluble in alcohol and in ether. Uracil is readily
soluble in ammonia. It is precipitated by mercuric nitrate, but not by
phosphotungstic acid. It is precipitated by silver nitrate only on the
careful addition of ammonia or baryta-water. Uracil gives the Weidel
reaction and the following reaction described by Wheeler and John-
son.5
The uracil solution is treated with bromine-water until it is per-
manently cloudy and then treated with baryta-water, when a purple or
violet-colored precipitate appears almost immediately. The coloration
1
Amer. chem. Journ., 29.
2
Zeitschr. f. physiol. Chem., 37 and 38.
* Ibid., 38. As it is not excluded, but rather probable according to Wheeler, that
besides thymine also other related pyrimidine bases such as isocytosine, 6-amino
pyrimidine and 6-oxpyrimidine can be formed in the hydrolytic cleavage of the nucleic
acids, Wheeler has prepared salts and compounds of these bodies and described them
as a matter of comparison, Journ. of biol. Chem., 3.
4
Ascoli, Zeitschr. f. physiol. Chem., 31; Kossel and Steudel, ibid., 37; Levene,
HA’L, 3S, 39; Levene and Mandel, ibid., 49; E. Fischer and Roeder, Ber. d. d. chem.
Gesellsel,., 34.
5
Journ. of biol. Chem., 3.
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