38 PHYSIOLOGICAL CHEMISTRY. 



neither tyrosin nor indol, in which it deviates from e albumins. 

 Still the aromatic group is not absent in gelatine, and it acts like 

 the oxidized albumin, the oxyprotsulphonic acid giving benzoic 

 acid (MALY). On treating gelatine with hydrochloric acid and 

 alcohol and then acting on this with a nitrite, BUCHNER and CUR- 

 TIUS obtained an ester of a diazo-fatty acid, probably diazo-oxyacry- 

 lic acid ester, and it is therefore also possible that the nucleus of 

 the gelatine is formed of amido-acrolein. 



Collagen is insoluble in water, salt solutions, dilute acids, and 

 ulkalies, but it swells up in dilute acids. By continuous boiling 

 with water it is converted into gelatine. It is dissolved by the 

 gastric juice and also by the pancreatic juice (trypsin solution) 

 when it has previously been treated with acid or heated with 

 water above -f- 70 C. By the action of ferrous sulphate, corrosive 

 sublimate, or tannic acid, collagen shrinks. Collagen treated by 

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

 great importance in the preparation of leather. 



Gelatine or glue 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. The solution is laevogyrate; a] at 

 -j- 30 C. = 130. Acetic acid and alkalies diminish the specific 

 rotary power. Gelatine solutions on boiling are not precipitated 

 either by mineral acids, acetic acid, alum, lead acetate, or mineral 

 salts in general. A gelatine solution acidified with acetic acid may 

 be precipitated by potassium ferrocyanide on carefully adding the 

 reagent, but on the addition of too much potassium ferrocyanide 

 the liquid remains clear. Gelatine 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 ; phosphomolybdic acid in the presence of acid ; and lastly by 

 alcohol, especially when neutral salts are present. Gelatine solu- 

 tions do not diffuse. Gelatine gives the biuret reaction, but not 

 ADAMKIEWICZ'S. It gives MILLON'S reaction and the xanthoproteic 

 acid reaction so faintly that it probably occurs from an impurity 

 consisting of albumin. By continuous boiling with water, espe- 

 cially in the presence of dilute acid, also by digesting with gastric 



