PROTEINS. 635 



Analytical reactions of tyrosine. 



1. Place a few crystals of tyrosine on a slide, and warm gently ; 

 they do not melt. (Crystals of fatty acids found in pus resemble 

 tyrosine in general appearance, but melt when heated, and are insolu- 

 ble in hydrochloric acid.) 



2. To a very small quantity of tyrosine add water and a few drops 

 of Millon's reagent. On boiling, the mixture turns rose red ; and 

 on standing a deeper red color develops. (All phenols and their 

 derivatives show this reaction.) 



3. Peria's reaction. Place a small quantity of tyrosine upon a 

 watch-glass, add a few drops of concentrated sulphuric acid, and 

 heat for half an hour over a boiling water-bath. Allow it to cool and 

 pour into 15 c.c. of water contained in a porcelain evaporating dish. 

 Warm, neutralize with powdered barium carbonate, filter while hot, 

 evaporate the filtrate to a few cubic centimeters, and add a very 

 dilute ferric chloride solution : a violet color appears. 



Leucine, C 5 H 10 .NH 2 .CO 2 H (Amino-caproie acid). This is a con- 

 stant product of the cleavage of proteins. It is easily soluble in 

 hot water, less so in cold water, soluble in alcohol, insoluble in ether. 

 It is easily soluble in acids and alkalies, forming crystalline com- 

 pounds with mineral acids. When impure, leucine crystallizes in 

 rounded lumps which often show radiating striations (Fig. 80). 

 AVhen pure it forms white, glittering, flat crystals. 



Analytical reactions of leucine. 



1. Heat slowly in a dry test-tube a very small portion of leucine ; 

 it sublimes in the form of woolly flakes. If heated above its melting- 

 point, 170 C. (338 F.), it decomposes into carbon dioxide and 

 amylamine, the latter substance having a characteristic odor. The 



reaction is this : 



C 6 H 13 N0 2 = C0 2 + C B H u NH a . 



2. Heat a little leucine in a dry test-tube, add a piece of caustic 

 soda and a few drops of water. Heat until the caustic soda melts, 

 when ammonia is given off. Allow to cool, dissolve in a little water, 

 and acidulate with dilute sulphuric acid : the odor of valeric acid is 

 noticeable. (Leucine, by this treatment, takes up oxygen and de- 

 composes into valeric acid, ammonia, and carbon dioxide.) 



3. Dissolve a little leucine in water, decolorize if necessary with 

 animal charcoal, filter, render alkaline with caustic soda, and add 

 2 drops of cupric sulphate solution. The cupric hydroxide which is 



