CH. IV.] LEUCINE. 97 



(v.) Neutralise to litmus paper with ammonia, and allow to 

 stand. Filter off the crystals of tyrosine, wash with cold 

 water, and dry in a warm oven. 



Properties of tyrosine. It crystallises from water in 

 white needles which are characteristically arranged in 

 sheaves. It is only very slightly soluble in cold water (i 

 part in 2490 parts of water at 17 C.), but more soluble in 

 hot water (i part in 150 parts). It is insoluble in ether, 

 acetone and absolute alcohol. It is readily soluble in 

 dilute alkalies and dilute mineral acids, but it is only very 

 slightly soluble in dilute acetic acid, and practically insoluble 

 in glacial acetic acid. Its melting point is rather indefinite, 

 but on rapid heating is 3 14 to 3 1 8. It is laevorotatory in 

 aqueous acid and alkaline solutions. 



On being heated in a tube it loses CO 2 , and is converted 

 to ^-oxyphenylethylamine. It is not precipitated by 

 phosphotungstic acid. It is precipitated by mercuric 

 sulphate, the precipitate being soluble in dilute sulphuric 

 acid. 



91. Morner's reaction. To a few cc. of Morner's reagent add 

 a trace of tyrosine and boil. A green colouration is produced. 



NOTE. The reagent is prepared by mixing i cc. of formalin with 45 cc. 

 of water and cautiously adding 55 cc. of strong sulphuric acid. 



92. Millon's reaction. To a trace of tyrosine add a few cc. 

 of water and a drop of dilute sulphuric acid and boil. Cool the 

 solution and add a few drops of Millon's reagent. A precipitate is 

 not obtained. Heat. A red colouration is obtained. 



NOTE. For the preparation of Millon's reagent, see Ex. 22. In the 

 presence of 5 per cent, sulphuric acid the red colour is produced in the cold. 



NH 2 



Leucine. 



a-amino-caproic acid (a-amino-iso-butyl-acetic acid). 



Leucine can be obtained by fractional crystallisation from a 

 protein digest, being separated by concentration of the 

 mother liquors left after the isolation of tyrosine. The 



