30 



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



glyoxylic acid solution, the colours obtained become identical. The 

 spectroscopic absorption is identical whichever reagent is employed. 



When sulphuric acid is a,dded to a solution of proteid in acetic acid 

 wholly free from glyoxylic acid, a considerable amount of charring 

 occurs, and the mixture becomes somewhat fluorescent. When, under 

 similar circumstances, very little glyoxylic acid is present, the reddish 

 colour obtained is still associated with fluorescence. But, when suffi- 

 cient of the glyoxylic acid is present, whether in acetic or aqueous 

 solution, to combine with the whole of the proteid product concerned 

 in the reaction, there is complete absence of charring and little or no 

 fluorescence. The solution becomes of a pure violet-blue colour. 



The coloured product of the Adamkiewicz reaction is usually stated 

 to show an absorption band between b and F in the position of the 

 urobilin band ; and Krukenberg described another between D and E. 

 Salkowski found the former to be inconstant, and we are convinced 

 that the latter alone is proper to the real product of the colour reac- 

 tion : the former, when seen, being due to some accessory effect of the 

 strong acids upon proteids. It is never seen in the original form of 

 the reaction unless the acetic acid employed is greatly deficient in 

 reactive power, and it is not observed with glyoxylic acid. The other 

 band is always present, and is identical after the use of a satisfactory 

 specimen of acetic acid and when a solution of glyoxylic acid is used. 



The band shrinks rapidly from its more refrangible edge on dilution 

 of the solution, its redward edge shifting but little. 



The following readings show the correspondence seen after employ- 

 ing acetic acid as obtained in the market (but with its active substance 

 concentrated by distillation) and that seen after the use of glyoxylic 

 acid in aqueous solution. The strengths were so arranged that, before 

 dilution, the colour of each solution appeared to be of the same 

 intensity. Witte's peptone was the proteid employed to obtain the 

 reaction : — 



Aqueous glyoxylic 

 Acetic acid. acid. 



Strong A 480 — A 625" A 480 — A. 630 



Diluted with an equal 



volume of sulphuric acid A 495 — X 625 A 495 — A 625 

 Diluted with thrice its 



volume of sulphuric acid A 530— A 610 A 530— A 615 



V. Other Sources of the Reactive Substance. 



Of the typical two-carbon compounds — glycol, glycollic aldehyde, 

 glycollic acid, glyoxal, glyoxylic acid, and oxalic acid — none but the 

 aldehyde-acid (glyoxylic acid, HCO.COOH or CH(OH) 2 .COOH), gives 

 the smallest indications of yielding a colour-reaction with proteid on 

 addition of sulphuric acid. It would seem that the reaction is not 



