372 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



A. Colour Reactions. 



The colour reactions for proteins are generally positive. 



B. Coagulation Reactions. 



* (i) No coagulum is formed on boiling the solution after acidifying 

 with a drop of acetic acid. 



* (2) A white precipitate is formed on adding nitric acid, drop by 

 drop, especially in presence of salts. This precipitate dissolves on 

 heating, but reappears on cooling. 



(3) Alcohol precipitates the proteoses more or less entirely ; the 

 precipitate is not coagulated by standing in contact with alcohol and 

 redissolves on adding water. 



C. Precipitation Reactions. 

 (a) Heavy Metals. 



* The solution is precipitated by solutions of the heavy metals : 

 copper sulphate, lead acetate, mercuric chloride. 



(b) Alkaloidal Reagents. 



* (I) A white precipitate is formed on adding a drop of glacial 

 acetic acid and 2 or 3 drops of potassium ferrocyanide. This pre- 

 cipitate dissolves on heating but reappears on cooling. 



* (2) Tannic acid gives a white precipitate. 



* (3) Other alkaloidal reagents also produce precipitates. 



SEPARATION OF PROTEOSES AND PEPTONE. 



The mixture of derivatives obtained by the hydrolysis of a pro- 

 tein is separated by salting out from the solution. Saturation with 

 sodium chloride or magnesium sulphate produces the same effect as 

 half saturation with ammonium sulphate or zinc sulphate. Ammon- 

 ium sulphate is used almost exclusively. 



(i) Primary Proteoses. 



* A white precipitate of primary proteoses is formed when an ex- 

 actly equal volume of saturated ammonium sulphate solution is added 

 to a solution of Witte's peptone (20 or 25 c.c. should be used in testing). 

 If the mixture be well stirred with a glass rod covered at the end with a 

 piece of rubber tubing, the precipitate may gather upon the end of the 

 rod and can be almost completely removed in this way, otherwise it is 

 separated by filtering. 



The mass thus collected may be dissolved in warm water. The 

 cold solution will give the previous reactions for the mixture of pro- 

 teoses and peptone. 



This precipitate according to Haslam contains three substances ;-^ 



a-protoproteose. 

 /3-protoproteose* 

 Jieteroproteose. 



