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120 THE PROTEIN SUBSTANCES.
solution; thus certain substances such as sulphates, citrates, acetates,
and glycerin may accelerate, while the chlorides, chlorates, bromides,
alcohol, and urea retard, this power.
Gelatin solutions are not precipitated on boiling, or by mineral
acids, acetic acid, alum, basic lead acetate, or metallic salts in general. A
gelatin solution acidified wjth acetic acid may be precipitated by potas-
sium ferrocyanide on carefully adding the reagent. Gelatin solutions
are precipitated by tannic acid in the presence of salt, and according to
Trunkel l
completely if the gelatin and tannic acid are in» the propor-
tion 1 : 0.7. According to him the precipitation is not due to a chemical
combination but to an adsorption phenomenon. Solutions of gelatin
in water are also precipitated by acetic acid and common salt in sub-
stance; mercuric chloride in the presence of HC1 and NaCl; by meta-
phosphoric acid and phosphomolybdic acid in the presence of acid;
and lastly also by alcohol, especially when neutral salts are present.
Gelatin solutions do not diffuse. Gelatin gives the biuret reaction,
but not Adamkiewicz-Hopkins reaction. It gives Millon’s reaction
and the xanthoproteic reaction so faintly that they probably occur from
impurities consisting of proteids. According to C. Morner, pure gelatin
gives a beautiful Millon’s reaction, if not too much reagent is added.
In the other case no reaction or only a faint one is obtained.
By continued boiling with water gelatin is converted into a non-
gelatinizing modification called /3-glutin by Nasse. According to Nasse
and Kruger the specific rotatory power is hereby reduced from — 167.5°
to about— 136°.2
According to Trunkel, who has especially studied
the rotation behavior of gelatin, the rotation of /3-glutin is less than the
ordinary a-glutin. On prolonged boiling with water, especially in the
presence of dilute acids, also in the gastric or tryptic digestion, the gelatin
is transformed into gelatin proteoses, so-called gelatoses and gelatin
peptones, which diffuse more or less readily.
According to Hofmeister two new substances, semiglutin and hemicollin,
are formed. The former is insoluble in alcohol of 70-80 per cent and is precipitated
by platinum chloride. The latter, which is not precipitated by platinum chloride,
is soluble in alcohol. Chittenden and Solley 3
have obtained in the peptic
and tryptic digestion a proto- and a deutero-gelatose, besides a true peptone. The
elementary composition of these gelatoses does not essentially differ from that of
the gelatin.
Paal * has prepared gelatin-peptone hydrochlorides from gelatin by the
action of dilute hydrochloric acid. These salts are partly soluble in ethyl and
1
Bioch. Zeitschr., 26.
2
Nasse and Krtiger, Mary’s Jahresber., 19, p. 29. In regard to the rotation of
/3-glutin. see Framm, Printer’s Arch., 68; Trunkel, 1. c.
3
Hofmeister, 1. c; Chittenden and Solley, 1. c.
1
Her. d. deutsch. chern. Gesellsch., 25.
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