250 EEACTIONS OF TYROSINE. [BOOK II. 



in alcohol and ether. It is decomposed by evaporating its solutions. 

 It has the composition represented by the formula (C 9 H 10 NO 3 ) 2 Cu l . 

 In the detection of tyrosine the observer is much aided by the 

 study of the crystalline form, as well as of the solubility in various 

 agents. In addition, however, several reactions are available. 



Reinhoid Tyrosine forms several compounds with mercury ; 



Hoffmann's re- all these when heated with a solution containing 

 action 2 . nitrous acid are coloured red. Millon's reagent is 



employed in testing for tyrosine. When added to solutions of 

 this body it produces a precipitate and, on boiling, the liquid as- 

 sumes a red colour, which increases in depth as the boiling is con- 

 tinued. Millon's reaction for the detection of proteid bodies and 

 their derivatives depends upon the action exerted by mercuric salts, 

 in the presence of nitrous acid upon the tyrosine residue which they 

 contain. Nevertheless, no solution of a proteid, however concen- 

 trated, exhibits the progressively increasing colour commencing with 

 a pink shade and passing into a deep crimson which is seen when 

 solutions of tyrosine are boiled with Millon's reagent. Maly recom- 

 mends that the liquid to be tested for tyrosine be first treated with 

 a not too acid solution of mercuric nitrate, and then either with a 

 little nitric acid, containing nitrous acid, which is diluted before 

 being added, or with a nitrite. 



Piria's re- A small quantity of tyrosine is placed on a watch- 



glass together with one or two drops of concentrated 

 sulphuric acid and is heated on the water bath to 50 C. After half- 

 an-hour the solution is diluted with a little water and neutralised 

 by means of barium carbonate. On filtering and adding to the 

 nitrate a dilute solution of ferric chloride, free from acid, a violet 

 colour developes. An excess of ferric chloride decolourises the solu- 

 tion. When, besides tyrosine, large quantities of leucine are present, 

 Piria's reaction is interfered with. 



Piria's reaction depends upon the formation of compounds of tyrosine 

 and sulphuric acid. 



Scherer's When tyrosine is treated with a mixture of 1 part 



reaction. O f concentrated nitric acid and 1 part of water and the 



mixture is evaporated to dryness a deep yellow residue is obtained, 

 which on being moistened and warmed with sodium hydrate solution 

 assumes at first a yellow and afterwards a deep reddish-yellow colour. 

 Scherer's reaction depends upon the formation of nitrate of; nitro- 

 tyrosine C 9 H 10 (N0 2 )N0 3 . HNO 3 . 



1 Franz Hofmeister, c Zur Kenntniss der Amidosauren. ' Maly's Jahresbericht, 

 Vol. vn. (1878), pp. 79 and 80. The original paper appeared in the Sitzungsber. der 

 Wien. Akad. (1877), but the author has been unable to consult it. 



2 Reinh. Hofmann, 'Reaction auf Leucin und Tyrosin,' Ann. d. Chemie, &c. 

 Vol. LXXXVII., p. 123. 



