6 CHEMISTRY OF THE PROTEIDS CHAP. 



Rose 1 in 1833 was the first to observe this reaction with albumin. 

 It was discovered quite independently and investigated more fully by 

 Piotrowski 2 in 1857. Wiedemann 3 had previously, in 1849, found 

 biuret to give a rose-red reaction, and since his time this reaction has 

 been known as 'the biuret -reaction.' Gnezda 4 in 1889 showed 

 albuminous substances to give yellow and orange reactions if nickel 

 was substituted for copper; and Pickering 5 in 1893 found cobalt 'to be 

 an even more delicate test than copper, while no definite reactions were 

 obtained with the salts of iron, manganese, and zinc. The first 

 explanation of Rose's reaction we owe to Schiff, as is more fully 

 explained on p. 141. 



The biuret-reaction is of special interest because it differs from all 

 other reactions in not being obtainable with any but the albuminous 

 dissociation-products of ' proteids.' It is therefore generally used if we 

 wish to distinguish between albumins and their simpler or secondary 

 decomposition-products. A sharp line of demarcation between these 

 compounds cannot, however, always be drawn. (See pp. 118, 144, 149.) 



Stokvis 6 and Salkowski 7 draw attention to the fact that urobilin 

 produces with sodium hydrate and copper sulphate a colour which is 

 undistinguishable from that of the biuret-reaction. 



\/ 



2. The Xanthoproteic-Reaction of Fourcroy and Vauquelin 



On adding a strong solution of nitric acid to a watery solution of 

 an albumin or to a solid albumin, as contained, for example, in a piece of 

 bread, there is produced either in the cold, as in the case of bread, but 

 usually only after heating, a deep yellow coloration, which on the 

 addition of soda solution becomes reddish brown, while with ammonia 

 it turns a vivid orange colour. 



This reaction was first noticed by Fourcroy and Vauquelin, 8 who 

 called the product ' the yellow acid ' ; they also noted its very bitter 

 taste. Fiirth 9 has shown the reaction to depend on the formation of 



1 F. Rose, Poggendor/'s Ann. 28. 132 (1833). 



2 G. v. Piotrowski, Sitzb. Akad. d. Wiss. Wien, math.-natunv. Glasse, 24. 335 

 (1857). 



3 G. Wiedemann, Poggendorfs Ann. 74. 67 (1849). 



4 J. Gnezda, Proc. Roy. Soc. 47. 208 (1889). 



N5 J. W. Pickering, Journ. of Physiol. 14. 347 (1893). 



6 H. B. J. Stokvis, Zeitschr. f. Biol. 34. 466 (1896). 



7 E. Salkowski, Berl. klin. Wochensch. 1897, No. 17. - 



8 Fourcroy and Vauquelin, Ann. Cliim. 56. p. 37 [30 vendemiaire an XIV. i.e. 

 1805]. (See also Berzelius, Medico-Chirurg. Trans. 3. 205 (1812).) 



9 0. v. Fiirth, Einwirkung von Salpetersdure auf Eiweissstoffe, Habilitationsschrift 

 (Strassburg, 1899). 



