138 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



II. CONDUCT OF GELATIN (GLUTIN). 



Use a solution of commercial gelatin (the best white gel- 

 atin) for the following experiments. 



About 5 g. of gelatin are covered with water in an evapo- 

 rating-dish and allowed to stand. On the next day or after 

 several hours it will appear much swollen, but not dissolved. 

 The supernatant fluid is poured off, 40 cc. of water added, the 

 mixture heated on the water-bath until the gelatin is dis- 

 solved, and then cooled: very soon a tolerably firm jelly will 

 be obtained. To this add 190 cc. more of water and warm 

 again. The solution thus obtained, about 2 per cent., is to 

 be used for the following reactions after it has cooled some- 

 what: 



1. Portions of the solution are treated in test-tubes 

 with (a) tannin solution, and also with (6) hydrochloric and 

 phosphotungstic acids: voluminous precipitates. General 

 conduct of all proteids, their immediate derivatives (albu- 

 moses and peptones), and also of the albuminoids. 



2. Boiling the solution produces no precipitate even when 

 acetic acid is added. 



3. The addition of acetic acid v and potassium ferrocyanide 

 produces no precipitate (distinction from albumin and albu- 

 moses) ; under certain conditions, however, a precipitate may 

 be formed (Morner). 1 



4. The addition of mercuric chloride gives no precipitate 

 (distinction from albumoses and peptone). 



5. Boiling after the addition of one-third of its volume of 

 nitric acid produces only a very faint yellow color; gelatin 

 yields only extremely little so-called xanthoproteic acid, as 

 the aromatic group is almost entirely lacking in the molecule, 

 and the phenol or tyrosine group especially is absent. 



6. The addition of sodium hydroxide and some copper 



1 Zeitschr. f . physiol. Chem. 28, 489. 



