TESTS FOR PEPTONES 165 



carbonate and warming on the water-bath. In the latter case the 

 sulphate is precipitated as barium sulphate, and the ammonia may 

 be driven off by heat, leaving the proteoses in solution. The 

 proteose may be precipitated from the concentrated solution by 

 filtering it directly into alcohol, from which it may be separated 

 by filtration. It may be dried as in the preparation of the other 

 proteids. Make the following tests upon the proteids in solution : 



1. The biuret test gives a rose- red coloration. 



2. Try the following precipitants and notice that the precipi- 

 tate disappears on heating and reappears on cooling in every 

 case. 



(a) Picric acid. 



(b) Potassio-mercuric-iodide, and hydrochloric acid. 



(c) Trichloracetic acid. 



(d) Acetic acid and saturation with sodium chloride. 



232. Tests for Peptones. The filtrate obtained in the separation 

 of the proteoses should be extracted once or twice with one-fifth 

 volume of 95 per-cent. alcohol, and the alcoholic solutions after 

 filtration and concentration should be treated with barium carbo- 

 nate for the purpose of removing the sulphate still in the solution. 

 When this has been done the fluid should be evaporated to a 

 small bulk and filtered into absolute alcohol. The peptones are 

 precipitated by this process and may be removed in the same 

 manner as proteose. 



Perform the following tests for peptones in solution : 



1 . Precipitate by tannic acid, phospho-molybdic acid, phospho- 

 tungstic acid, and absolute alcohol. 



2. Diffusion. Place some of the solution in a parchment shell 

 and suspend in a beaker of water. After several hours test the 

 water for proteid by the biuret reaction. This test gives a rose- 

 red color with the peptones. 



3. Acidulate strongly with acetic acid and then add potassium 

 ferrocyanide. No precipitate. 



233. Determination of Proteids Soluble in Alcohol. Certain pro- 

 teids are not removed from tissues by the saline solution, but after 



