286 METHODS OF IDENTIFICATION AND STUDY 



The precipitate may be absent even when the odour 

 is pronounced. 



2. Add Schiff's reagent. 



Violet or red colour = aldehyde. 



3. To 10 c.c. of solution add 2.5 c.c., 25 per cent, 

 sulphuric acid, and a crystal or two of potassium 

 bichromate and distil. Reduction of the bichromate 

 to a green colour and a distillate, which smells of acet- 

 aldehyde and reacts with Schiff's reagent, shows the 

 presence of alcohol in the original liquid. 



4. Add a few drops of sodium nitroprusside solution, 

 make alkaline with ammonia, then saturate with 

 ammonium sulphate crystals. Acetone gives little 

 colour on the addition of ammonia, but after the addi- 

 tion of ammonium sulphate a deep permanganate 

 colour, which takes ten minutes to reach its full inten- 

 sity. Aldehyde gives a carmine red unaltered by 

 ammonium sulphate. 



5. Indol Production. 



Media Required: 



Inosite-free bouillon (vide page 183). 

 Or peptone water (vide page 177). 

 Reagents Required: 



Potassium persulphate, saturated aqueous solution. 

 Paradimethylamino-benz aldehyde solution. This is prepared by 

 mixing: 



Paradimethylamino-benzaldehyde ... 4 grammes 



Absolute alcohol 380 c.c. 



Hydrochloric acid, concentrated .... 80 c.c. 



METHOD. 



Prepare several test-tube cultivations of the 

 organism to be tested, and incubate. 



Test for indol by means of the Rosindol reaction in 

 the following manner. (If the culture has been incu- 

 bated at 37 C., it must be allowed to cool to the room 

 temperature before applying the test.) 



i. Remove 2 c.c. of the cultivation by means of a 

 sterile pipette and transfer to a clean tube, then, 



