GELATIN. 119 



or heated with^ water above 70 C. 1 By the action of ferrous sulphate, 

 corrosive sublimate, or tannic acid, collagen shrinks greatly. Collagen 

 treated by these bodies does not putrefy, and tannic acid is therefore of 

 great importance in the preparation of leather. 



Gelatin or glutin is colorless, amorphous, and transparent in thin 

 layers. It swells in cold water without dissolving. It dissolves in warm 

 water, forming a sticky liquid, which solidifies on cooling when sufficiently 

 concentrated. As PAULI and RoNA 2 have shown, various bodies may 

 have a different influence upon the gelatinization-point of a gelatin 

 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; by acetic acid and 

 common salt in substance ; mercuric chloride in the presence of HC1 and 

 NaCl ; by metaphosphoric 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'S. 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 /?-glutin by NASSE. According to NASSE 

 and KRUGER the specific rotatory power is hereby reduced from 167.5 

 to about 136 . 3 On prolonged boiling with water, especially in the 

 presence of dilute acids, also in the gastric or tryptic digestion, thfe 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 hemi- 

 collin, are formed. The former is insoluble in alcohol of 70-80 per cent 

 and is precipitated by platinum chloride. The latter, which is not pre- 

 cipitated by platinum chloride, is soluble in alcohol. CHITTENDEN and 

 SOLLEY 4 have obtained in the peptic and tryptic digestion a proto- and 



1 Kiihne and Ewald, Verb. d. Naturhist. Med. Vereins in Heidelberg, 1877, 1. 



2 Hofmeister's Beitrage, 2. 



3 Nasse and Kriiger, Maly's Jahresber., 19, p. 29. In regard to the rotation of 

 /?-glutin, see Framm, Pfliiger's Arch., 68. 



4 Hofraeister, 1. c.; Chittenden and Solley, 1. c. 



