194 THE PRODUCTS OF ALL I'M ISO US UK1ESTION. 



according to some observers the entire amount of sulphur is split 

 off from the albuminous molecule in the form of the chromogen, 

 others maintain that the sulphur of the proteinoehromes is referable 

 t<> contamination with other substances. 



With bromine three pigments at least may be obtained, viz., a 

 bluish-violet subetance, which contains about 35 per cent, of bro- 

 mine ; a red body, with 27 percent.; and a brown pigment, with the 

 same amount of bromine. The violet pigment, moreover, is said to 

 contain a considerable amount of iron, but it is noteworthy that 

 albumins which are free from iron also give rise to the formation 

 of proteinoehromes. 



Breitler has isolated a chloroproteinochrorne, to which he gives 

 the formula C % H 119 N 21 O 3 S. This does not coincide with any one of 

 the three bodies that have been just referred to, but it is quite pos- 

 sible that still other chromogens exist. 



According to Nencki, a certain similarity exists in the percentage 

 composition of the red pigment with hsemoporphyrin, viz., bilirubin, 

 and of the brown pigment with the so-called melanins. The tryp- 

 tophan, moreover, like hsematin and haematoporphyrin, yields pyrrol, 

 hydrogen sulphide, methyl-mercaptan, and skatol on fusing with 

 caustic alkali. 



Test. The test for tryptophan and the isolation of the three 

 known pigments are conducted as follows : the digestive mixture 

 is acidified with acetic acid and treated with two and one-half times 

 its volume of saturated bromine-water. A beautiful reddish-violet 

 precipitate is thus formed, which increases on standing. After 

 twenty-four hours this is filtered off. On the further addition of 

 bromine-water the brown pigment separates out on standing. The 

 red pigment will be found in the violet precipitate, and can be iso- 

 lated as follows : the precipitate is first washed with water and then 

 extracted with dilute ammonia ; this extract is precipitated with 

 acetic acid. The precipitate is separated from the brown filtrate, 

 redissolved in very dilute ammonia, again precipitated with acetic 

 acid, and washed with water. It is then extracted with amyl 

 alcohol ; this dissolves the red body. The alcohol is evaporated 

 off at 40 C., the residue dried at 106 C., and finally washed with 

 ether. The violet pigment is obtained on further extraction of the 

 violet precipitate with a little stronger solution of ammonia than in 

 the first instance. The substance is precipitated with acetic acid, 

 well washed with water, and extracted with 95 per cent, alcohol. 

 The alcoholic extract is evaporated to dryness at 40 C., the residue 

 dried at 106 C. and washed with petroleum ether. 



To isolate the brown pigment, finally, the second bromine pre- 

 cipitate is filtered off, washed with water, dissolved in very dilute 

 ammonia, reprecipitated with acetic acid and washed with water, 

 and briefly with 95 per cent, alcohol, both of which dissolve a por- 

 tion of the pigment. It is then dried and washed with ether. The 

 resulting product is almost black. 



