234 AMIDES. [CH. X 



Peptones and Albumoses. 



Remove excess of copper from the filtrate by HjS — 

 warm to expel excess of HjS and concentrate the liquid if 

 necessary. 



Test portions of this solution for peptones and albu- 

 moses by : — 



(1) Biuret test [an equal volume of strong soda 

 (NaOH) solution and adding one or two drops only of 

 dilute copper sulphate solution]. 



Peptones and albumoses give a characteristic colour of 

 a redder tint than biuret. 



(2) Sodium phosphotungstate and dilute sulphuric 

 acid. 



Peptones and albumoses give a white precipitate. 



(3) Saturated alcoholic solution of mercuric chloride. 

 Peptones and albumoses give a white precipitate in- 

 soluble in water when once thrown down. 



Amides. 



If peptones and albumoses are present remove by adding 

 alcoholic mercuric chloride as long as it causes a precipitate 

 — filter — evaporate oif alcohol from filtrate and remove 

 excess of mercury from solution by HaS. After warming 

 to remove HjS exactly neutralize solution with dilute soda 

 and test portions for amides by 



(1) Addition of freshly precipitated and well washed 

 cupric hydroxide. 



Amides form a deep blue liquid with solution of the 

 hydroxide — if this liquid is carefully evaporated and al- 



