22 



Messrs. F. G. Hopkins and S. W. Cole. 



test, in which /3-naphthol and sulphuric acid are added to a proteid 

 solution. While in the latter the added naphthol is held to react with 

 furfurol from the proteid ; in the Adamkiewicz reaction both the fur- 

 furol and a substance capable of reacting with it are supposed to be 

 liberated from the proteid molecule. Such we believe is the prevalent 

 view. Of late years, the Adamkiewicz reaction has been much em- 

 ployed as giving evidence for the presence of carbohydrate groups in 

 certain proteid derivatives, and of its absence from others. More than 

 one writer," 55 ' however, has referred to an element of uncertainty in the 

 reaction, and it is easy to gather from the literature that this has been 

 commonly observed.! 



In what follows it will be shown that the mechanism of the reaction 

 has been wholly misunderstood. Proof will be given that the use of 

 acetic acid introduces an extraneous and perfectly specific factor into 

 the reaction, involving the addition of a substance quite necessary to 

 the formation of the coloured product. This substance, moreover, is 

 not acetic acid itself but an impurity, which, though very generally 

 present, is admixed in varying quantity, and is occasionally absent. 



I. The Reaction due to an Impurity in Acetic Acid. 



We were led to pursue the following investigation by observing that, 

 with a specimen of acetic acid in use in this laboratory last year, it 

 was impossible under any circumstances to obtain the Adamkiewicz 

 reaction. 



No matter what form of proteid might be employed, when its solu- 

 tion in this acetic acid was mixed with sulphuric acid, a yellow or 

 brown, slightly fluorescent mixture was all that could be obtained. No 

 modification in the order of the procedure, or in the proportion of the 

 two acids employed, resulted in the production of any trace of reel or 

 violet colour. 



We afterwards obtained a number of specimens of acetic acid from 

 various makers, and were surprised to find that no small proportion of 

 these gave equally negative results ; while, of the remainder, some 

 yielded a much more intense reaction than others, although employed 

 under precisely similar conditions. 



Either, therefore, the negative result with particular specimens was 

 due to the presence of some impurity capable of interfering with the 

 production of colour, or the reaction itself must be due to a sub- 

 stance commonly, though not universally, present as an impurity in 

 acetic acid. 



We soon obtained evidence that the latter alternative must be 

 accepted. For we found that whenever a specimen of glacial' acetic 



* Cf Halliburton, ' Schafer's Text Book of ^Physiology/ vol. 1, p. 47. 

 f Cf Salkowski, 'Zeitsch. f. pliysiol. Chem.,' vol. 12, pp. 220, 222. 



