THE PROTEINS 367 



Proteins, precipitated by alcohol and washed with ether, give a blue colour 

 when heated with concentrated hydrochloric acid. (Liebermann's reaction.) 

 A reddish-violet colour, which ultimately becomes brown, is produced on 

 heating proteins with concentrated hydrochloric acid. 



These reactions, according to Cole, are due to the presence of trypto- 

 phan : in the first, glyoxylic acid is derived from the alcohol and ether : in 

 the second, furfural is formed from carbohydrate in the protein and reacts 

 with the tryptophan. 



The green to blue colour produced when proteins are heated with ben- 

 zaldehyde, a drop of ferric chloride and concentrated hydrochloric acid 

 (Reichl's reaction) is also due to the presence of tryptophan. 



(6) Molisch's. 



A few drops of a-naphthol solution are added to the protein solu- 

 tion and mixed thoroughly. Concentrated sulphuric acid is run under 

 the solution. At the junction of the two liquids a purple-red ring is 

 formed. 



This reaction is due to the formation of furfural from the carbo- 

 hydrate radicle in the protein and to its combination with a-naphthol. 



