G. Williams 187 



obtained. The yellow precipitate of histidine mercury sulphate was 

 allowed to stand for twenty-four hours, filtered off, washed with 5 per 

 cent, sulphuric acid, suspended in water and decomposed with hydrogen 

 sulphide. The mercury sulphide was filtered ofi, washed, and the 

 sulphuric acid removed quantitatively from the filtrate and washings 

 by baryta. The liquid was then made up to 250 c.c, and two Kjeldahl 

 nitrogen determinations made. 



25 c.c. gave NHg equal to 15 c.c. N/10 acid. 

 25 c.c. gave NHg equal to 15 c.c. N/10 acid, 



= 0-021 grm. N. 

 250 c.c. contain 0*21 grm. N 



= 0-775 grm. histidine. 

 Allowing for portions removed for analysis, this weight becomes 

 0-833 grm. histidine. 



(6) The filtrate from the histidine mercury sulphate was freed from 

 mercury by hydrogen sulphide and from sulphuric acid by neutralising 

 to litmus with baryta, and adding barium nitrate as long as a precipi- 

 tate was formed. Both precipitates were filtered ofi and washed. The 

 solution was then concentrated to 300 c.c, acidified with nitric acid, 

 and treated with silver nitrate, as before, till a test drop gave a yellow 

 colour with baryta. The solution was nearly neutralised to litmus 

 with baryta, and then a suspension of barium carbonate was added, 

 and the mixture warmed on the water bath^, and finally brought to the 

 boil on a sand bath. Upon cooling, the precipitate of histidine silver 

 was filtered off, washed with dilute baryta water (10 drops saturated 

 cold solution per 100 c.c). The precipitate was then decomposed in 

 the usual way, and the solution made up to 250 c.c. 



25 c.c. gave NHg equal to 4-65 c.c. N/10 acid 



- 0-00651 grm. N. 

 250 c.c. contain 0-0651 grm. N. 



0-0651 grm. N = 0-2402 grm. histidine. 

 Increasing this so as to allow for losses due to analysis, it becomes 



0-2583 grm. 



Total weight of histidine obtained 0-833 grm. -\- 0-258 grm. 



= 1-091 grm. 



— 3-04 per cent, in the protein. 



The histidine was then isolated as the hydrochloride. 



1 Vide Steudel, Handb. der Biochem. Arbeit, ii, 498, 1910. 

 Journ. of Agric. Sci. viii 13 



