282 Journal of the Asiatic Society of Bengal. [N.S., XIII, 



to 3 cc. of concentrated sulphuric acid and the mixture heated 

 for about two minutes with a few drops of lactic acid, prefer- 

 ably in a water-bath, it will assume a yellowish colouration, 

 changing rapidly to yellowish red. and finally to reddish brown. 

 Glycolic acid, on being subjected to a similar treatment, yields 

 an intense blue colouration or greenish blue precipitate depend- 

 ing on the amount of the acid present. The reaction is highly 

 sensitive, and may with advantage be employed for the detec- 

 tion of the acid in sour milk or urine. As in the previous case, 

 the mechanism of the reaction consists, first of all, in the split- 

 ting up of the acids into the respective aldehydes, and the 

 latter then bring about the characteristic changes. 



The well-known morphine reaction may also be similarly 

 utilised. If carried out as before, lactic acid yields a yellow- 

 changing to red or reddish brown, and glycolic acid a deep 

 violet colouration. For considerations stated below it appeared 

 interesting to study the reaction of indole with the two alde- 

 hydes. The behaviour of this substance towards formalde- 



CH 



CH 

 CH 



CH N 



H 



Indole. 



hyde and acetaldehyde, and therefore towards glycolic and 

 lactic acids, appears to be similar to that of morphine. The 

 only perceptible difference is in the intensity of the colouration 

 produced with formaldehyde. The difference is thus one of 

 degree and not of kind— the violet tint given by morphine 

 being of a deeper shade than that of indole. In fact but for 

 its comparatively high cost indole might be used as a reagent 

 tor the detection of the two aldehydes, as also of lactic and 



fflvcolic anifU 



glycolic acids. 



be mentioned that Rosenheim has observed (Bio-Chemical 

 Journal, 1906, i 233-240) that formaldehyde also produces a 

 similar violet colouration when treated with proteins in the 

 presence of concentrated sulphuric acid. Salmon Acree (Ameri- 



2Lv*"! J0Uma1 ' 1907 ' 37 > 604 - 61 °) has repeated Rosen- 

 fn ^ S eXP0rim , entS ,° n a lar S e scale > and ^ving applied the test 

 Hnt^w"!^ ° f « ubBtM «»8, has arrived at the general con- 

 clusion that the production of a violet colouration with for- 



