PROTEINS. 83 



cine (the tyrosine will be practically insoluble) and filter. Concen- 

 trate the filtrate and allow it to stand in a cool place over night for 

 the crude leucine to crystallize. Filter off the crystals and use them 

 in the tests for leucine given on page 84. The crystals of tyrosine 

 remaining on the paper from the first filtration may be used in the 

 tests for tyrosine as given below. If desired, the tyrosine and leucine 

 may be purified by recrystallizing in the usual manner. Habermann 

 has suggested a method of separating leucine and tyrosine by means 

 of glacial acetic acid. 





EXPERIMENTS ON TYROSINE. 



Make the following tests with the tyrosine crystals already pre- 

 pared or upon some pure tyrosine furnished by the instructor. 



1. Microscopical Examination. Place a minute crystal of ty- 

 rosine on a slide, add a drop of water, cover with a cover glass, and 

 examine microscopically. Now run more water under the cover 

 glass and warm in a bunsen flame until the tyrosine has dissolved. 

 Allow the solution to cool slowly then examine again microscopically 

 and compare the crystals with those shown in Fig. 23, page 72. 



2. Solubility. Try the solubility of very small amounts of tyro- 

 sine in cold and hot water, cold and hot 95 per cent alcohol, dilute 

 NH 4 OH, dilute KOH and dilute HC1. 



3. Sublimation. Place a little tyrosine in a dry test-tube, heat 

 gently and notice that the material does not sublime. How does this 

 compare with the result of Experiment 3 under Leucine? 



4. Hoffman's Reaction. This is the name given to Millon's 

 reaction when employed to detect tyrosine. Add about 3 c.c. of 

 water and a few drops of Millon's reagent to a little tyrosine in a 

 test-tube. Upon dissolving the tyrosine by heat the solution gradu- 

 ally darkens and may assume a dark red color. What group does 

 this test show to be present in tyrosine? 



5. Piria's Test. Warm a little tyrosine on a watch glass on a 

 boiling water-bath for 20 minutes with 3-5 drops of cone. H 2 SO 4 . 

 Tyrosine sulphuric acid is formed in the process. Cool the solution 

 and wash it into a small beaker with water. Now add CaCO 3 in 

 substance slowly with stirring, until the reaction of the solution is 

 no longer acid. Filter, concentrate the filtrate and add to it a few 

 drops (avoid an excess) of very dilute neutral ferric chloride. A 

 purple or violet color, due to the formation of the ferric salt of 

 tyrosine-sulphuric acid, is produced. This is one of the most satis- 

 factory tests for the identification of tyrosine. 



