1890.] 



A Cyanogen Reaction of Proteids. 



203 



G. Wiedemann* discovered that on adding* an alkaline solution of 

 copper sulphate to cyanuric acid, a violet solution was produced. 

 The same investigation showed that biuret gave a rose-red solution 

 on treatment with copper sulphate and sodium hydrate. 



One of the ordinary tests for a proteid, which is sometimes called 

 Piotrowski's reaction, is the violet solution produced by adding 

 copper sulphate and caustic potash or soda. Albumoses and peptones 

 differ from other proteids in giving with these reagents a rose-red 

 instead of a violet solution ; the colour so produced is the same as 

 that given by biuret, hence this reaction is generally spoken of as 

 the biuret reaction. It is stated that after heating any proteid 

 with caustic soda, and then adding copper sulphate, the rose-red 

 coloration of the biuret reaction appears ; and this is undoubtedly 

 the case, for the action of the hot concentrated alkali is to form not 

 only alkali-albumin, but also some substances of the albuinose class. 

 The whole value of the test in distinguishing between native albu- 

 mins on the one hand, and peptones and albumoses on the other, 

 depends on its being performed in the cold. 



Briickef especially has emphasised the difference between the 

 violet coloration given by ordinary proteids and the rose-red (so-called 

 biuret) reaction of the peptones. He however considers that the 

 radicle in the complex proteid molecule which gives rise to the reac- 

 tion is probably the same in. both cases, but that it is some other 

 change in the molecule that causes the difference of tint. 



SalkowskiJ has recently investigated the colour reactions of the 

 proteids, and shown that Millon's reaction and the Adamkiewicz 

 reaction are produced by the presence in the proteid molecule of 

 certain aromatic radicles. He does not, however, appear to have 

 investigated the biuret reaction ; and the object of my own work has 

 been to discover, if possible, upon what groups of atoms in the proteid 

 molecule this reaction depends. Whether the violet colour of ordi- 

 nary proteids is due to cyanuric acid, and the rose-red colour of 

 peptones to biuret, I am, however, unable to say. The main result of 

 my experiments has been that these reactions depend on the presence 

 in a proteid of cyanogen, or of some cyanogen-containing radicle. I 

 have also, by means of somewhat modifying the method usually 

 adopted for performing the test, discovered that it may be used for 

 distinguishing classes of proteids from one another more accurately 

 than has hitherto been possible. 



The chief modification I have introduced into the test has been the 

 addition of ammonia, either instead of or in addition to the potash or 



* < Poggendorff's Annalen,' vol. 74, 1849, p. 67. 



f Sitzungsberichte of the Vienna Academy, 1883, reprinted in ' Monatshefte f. 

 Chemie,' vol. 4. 



% < Zeitsch. f. Physiol. Chem.,' vol. 12. 



