H. M. Jones 431 
filtering. The acid filtrate is then treated with a sufficient quan- 
tity of concentrated solution of NagCO; to render the solution 
distinctly alkaline to phenolphthalein, whereupon the mercuric 
histidine is reprecipitated as a clean, creamy flocculent mass. 
The latter is thoroughly washed two or three times by suspending 
in water and refiltering as before, in order to remove NasCOs 
and NaCl. 
Finally, it should be suspended in about 600 cc. of water, and 
H2S allowed to bubble slowly through the thick suspension, until 
the mass becomes coal-black. The filtrate from this mass of 
HgS is then allowed to evaporate at room temperature, where- 
upon large yellowish crystals of histidine hydrochloride will sepa- 
rate out from the brown, syrupy mother liquor. The yield should 
be about 15 gm. The crystals are then freed from the brown 
adhering film of mother liquor, and dried between filters. It 
should be identified by its melting point (256°), by its crystalline 
structure, and 1s freedom from inorganic salts, proved by in- 
cinerating a small portion on platinum foil. 
