ISOLATION AND ESTIMATION OF TYROSINE 23 



l By acid hydrolysis. 



2 5 '2 after forty-eight hours. 



The bromination method thus does not decide whether the gravi- 

 metric value or the colorimetric value represents the tyrosine content 

 of protein the more accurately and consequently is of little value for 

 determining the tyrosine content of proteins. It may prove of use to 

 ascertain the amount of tyrosine in the impure tyrosine which is iso- 

 lated from proteins, if this impure tyrosine is shown to be free from 

 tryptophan. The gravimetric values may then be found to be higher 

 than those given by the various workers, who have usually only 

 weighed pure recrystallised tyrosine. 



