OH. Vlll.j TfcYPTlC DIGESTION. 217 



boiling water bath to about half its bulk. This is distributed into 

 small beakers (labelled B) and allowed to stand in a cool place for 

 24 hours for the tyrosine to separate out. The remaining portion 

 is distributed into test-tubes (labelled A) and allowed to stand for 

 24 hours. 



(i.) Bromine reaction for free tryptophane. If necessary filter A 

 from a crystalline precipitate of tyrosine. Acidify about 5 cc. with 

 a couple of drops of strong acetic acid and add bromine water, drop 

 by drop ; a pink colour gradually develops, which deepens and then 

 disappears as more bromine water is added. When the colour is 

 no longer intensified by the addition of bromine, add 2 or 3 cc. of 

 amyl or butyl alcohol and shake. On standing, the alcohol rises 

 to the surface coloured a fine red or violet. (See p. 93.) 



(ii.) Treat another 5 cc. of the filtrate with I cc. of 25 per cent, 

 sulphuric acid and 10 cc. of a 10 per cent, solution of mercuric 

 sulphate in 5 per cent. H 2 SO 4 . Shake the tube and leave it for 10 

 minutes. Note the yellow precipitate of a mercury compound of 

 tryptophane. Filter this off and label the filtrate C. Wash the 

 precipitate through a hole in the paper into a clean tube, fill with 

 water, shake and filter again, neglecting the filtrate. Wash the 

 precipitate on the paper once more with water and then let it drain. 

 Scrape a portion off the paper, transfer it to a tube, add 2 cc. of 

 " glyoxylic reagent " and then 2 cc. of concentrated sulphuric acid. 

 A purple colour is produced, showing that tryptophane is responsible 

 for the glyoxylic reaction. (See Ex. 23.) 



Treat another portion of the precipitate with Millon's reagent 

 and boil. A yellow colour is produced, not the characteristic red of 

 Millon's reaction. 



To another portion of the precipitate apply the xanthoproteic 

 test. A well-marked reaction is obtained. (See Notes to Ex. 21.) 



To portions of filtrate C apply the glyoxylic, Millon's and the 

 xanthoproteic reactions. Only the latter two are obtained, the 

 trytophane, but not the tyrosine, having been removed by the 

 mercury reagent employed. It will be noted that the solution 

 becomes bright pink as soon as the Millon's reagent is added. This is 

 due to the influence of the sulphuric acid. On heating the colour 

 may be discharged if an excess of the reagent be used, 



