REACTIONS OF ALBUMINOUS SUBSTANCES 7 



nitro-derivatives, and Salkowski 1 that the reaction indicates the presence 

 of aromatic radicals in the substance under investigation. Rohde 2 

 points out that a very intense reaction is obtained with tryptophane. 

 In addition to albumins this reaction is also obtained with many other 

 substances, such as the humins. (See p. 89.) 



3. The Reaction of Millon 



On boiling mercury with strong nitric acid until a portion of the 

 liquid no longer gives a precipitate with common salt ; adding strong 

 nitric acid to the concentrated solution of mercuric nitrate, Hg(N0 3 ) 2 ; 

 separating off the crystalline magma consisting of 2 Hg(N0 3 ) 2 + H 2 O, 

 there remains a thick mother liquor having the constant composition 

 Hg(N0 3 ) 2 + 2H 2 0. This solution possesses the power, first noticed 

 by Libavius, of colouring the skin a dark-red tint. Mercurous nitrate, 

 Hg(N0 3 ), is formed by the action of dilute nitric acid, in the cold, on 

 mercury. It is readily soluble in dilute nitric acid, and this solution 

 brought on to the skin colours it, first purple and then of a black tint. 



Millon's reagent is a solution of mercurous nitrate in nitric acid. 3 

 If it be added either to a watery solution of an albumin or to a suspen- 

 sion of solid albumin in water, or be poured, for example, over a piece 

 of bread, there is obtained either in the cold (as with bread), or after 

 boiling, a pink coloration of the fluid or a pink to blackish -red 

 coloration of the precipitated albumin. The reaction is given by all 

 oenzene derivatives in which one hydrogen atom has been replaced by 

 the hydroxyl group OH ; 4 and as tyrosin is the only oxyphenyl com- 

 pound in the proteid, 5 the reaction shows the presence of tyrosin. 

 The latter is contained in all albumins with the exception of gelatine 

 and certain albumoses and peptones. Inorganic salts in higher con- 

 centrations prevent the reaction. See also under tyrosin, p. 50. 

 This reaction has been very fully investigated by Vaubel 6 and by 

 Nasse, 7 whose papers are abstracted in the author's Physiological 

 Histology, pp. 321-323. 



' ' E. Salkowski, Zeitschr. f. physiol. Ghem. 12. 215 (1887). 

 2 E. Kohde, ibid. 44. 161 (1905). 

 1 Millon, Compt. Rend. 28. 40 (1849). 



4 A much fuller account, including the exact researches of Vaubel and Nasse, is given 

 in Mann's Physiological Histology, 1902, pp. 321-323 (Clarendon Press). 



5 E. Salkowski, Zeitschr. f. physiol. Ghem. 12. 215 (1887) ; 0. Nasse, Pftuger's 

 *Arch.f. d. ges. Physiol. 83. 361 (1901). 



6 Vaubel, Zeit. f. angeiv. Ghem. (1900), p. 1125. 

 17 Nasse, Pjtilger's Arch. 83. 361 (1901). 



