CHEMICAL BASIS OF THE ANIMAL BODY. 191 



The crystals are very sparingly soluble in cold water (1 in 2000 at 

 20), much more soluble in boiling water (1 in 1 50) ; they are almost 



FIG. 32. TYROSIN CRYSTALS. (Krukenberg.) 



insoluble in strong alcohol (1 in 13500) and quite insoluble in ether. 

 They are readily soluble in acids and particularly so in ammonia and 

 other alkalis and in solutions of alkaline salts. 



Preparation (i). The products of a prolonged pancreatic digestion 

 of proteids are neutralised and filtered ; the filtrate when concentrated 

 usually yields crusts of tyrosin crystals, which may be readily purified 

 by solution in a little boiling water from which they separate out on 

 cooling after concentration if necessary, (ii) Horn shavings are 

 boiled for 24 hours with sulphuric acid (5 of acid to 13 of water). 

 The sulphuric acid is then separated by the addition of lime, and 

 the filtrate from the calcium sulphate yields as before crusts of tyrosin 

 crystals on concentration and cooling. These are then purified by 

 recrystallisation from boiling water 1 . Any leucin at first present 

 in the crystalline crusts remains in the mother-liquors from which 

 the tyrosin has been separated. 



Apart from its crystalline form and characteristic solubilities tyrosin 

 may be readily recognised by several well-marked reactions. 



Hoffmann's reaction. When heated with Millon's reagent, solutions 

 of tyrosin yield a brilliant crimson or pink colouration which, if much 

 tyrosin is present, is accompanied finally by a similarly coloured preci- 



1 These methods suffice for the preparation of small amounts of tyrosin for 

 purposes of study. For full details of its preparation and most productive 

 separation from leucin see Hlasiwetz and Habermann, quoted sub leucin. See 

 also E. Schulze, Zt. f. pliysiol. Chem. Bd. ix. 1885, Sn. 63, 253, on the separation 

 of amido-acids. 



