294 PHYSIOLOGICAL CHEMISTRY 



tion mixture with, dilute hydrochloric acid. When nearly neutral, 

 exactly neutralize with 0.2% HC1 or with 0.2% sodium carbonate 

 to precipitate metaprotein. Filter, if necessary and concentrate 

 the nitrate, being careful to make the solution slightly acid with 

 acetic acid, as heating in alkaline solution will cause decomposi- 

 tion of the amino acids. The concentration may be carried on 

 over a free flame or wire gauze until the liquid becomes fairly 

 concentrated. The process then should be continued on a water 

 bath. To the resulting syrupy liquid, add alcohol as long as a 

 precipitate of proteoses and peptones forms. Remove as much 

 as possible of this sticky precipitate, warm slightly, and filter. 

 The alcoholic filtrate contains leucine and tyrosine. Concentrate 

 the alcoholic solution on the water bath and allow it to stand in 

 a cool place (over night if possible). Tyrosine, being the more 

 insoluble of the two amino acids, crystallizes first. Leucine comes 

 down more slowly. When a good crop of crystals has been 

 obtained, filter them off, add a small amount of water and warm 

 gently. Leucine goes into solution while tyrosine remains undis- 

 solved. Concentrate the leucin-filtrate and allow it to stand 

 (over night if necessary). 



(1) Tyrosine. 



88. Observe the crystal form with the microscope. Tyrosine 

 crystallizes in fine needles, which often group into rosettes or 

 sheaves. If the crystals are not well formed, add a drop of water, 

 warm, and allow to cool slowly. 



89. Observe that tyrosine is quite insoluble in cold water, 

 but much more soluble in hot. 



90. Perform Millon's test with a small amount of tyrosine. 



(2) Leucine. 



91. Observe the crystals under the microscope (broad plates). 



92. Record solubility of leucine in cold water and hot water. 



93. Salts of Amino Acids. The copper salts of the amino 

 acids are extremely serviceable in separating these compounds, 

 as their solubilities vary considerably. To a solution of either 

 tyrosine or leucine, preferably the former, in hot water, add a 

 few drops of diluted copper sulphate solution. Observe the blue 



