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 with 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 1 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 deuter o-gelatose, besides a true peptone. The 

 elementary composition of these gelatoses does not essentially differ from that of 

 the gelatin. 



PAAL 4 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 Kriiger, Maly's Jahresber., 19, p. 29. In regard to the rotation of 

 /3-glutin. see Framm, Pfliiger's Arch., 68; Trunkel, 1. c. 



3 Hofmeister, 1. c.; Chittenden and Solley, 1. c. 



4 Ber. d. deutsch. chem. Gesellsch., 25. 



