252 AMIDES. [CH. X 



Peptones and Albumoses. 



Remove excess of copper from the filtrate by HgS — 

 warm to expel excess of H3S 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 off alcohol from filtrate and 

 remove excess of mercury from solution by H^S. After 

 warming to remove H2S, 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 



