REAGENTS AND QUALITATIVE METHODS 139 



to 10 drops of a potassium permanganate solution (2 grams 

 to 1000 ex.). In the presence of citric acid the solution 

 becomes colorless and a white precipitate is formed. 



Abderhalden, E., Handbuch der Biochemischen Arbeitsmethoden, Bd. 5, 

 p. 409, 1913. 



Tests for Indol and Skatol: 



(A) I. Add a few drops of a 5 per cent, solution of 



vanillin in 95 per cent, alcohol to 5 or 6 c.c. of 

 the indol solution. 



2. Make the mixture strongly acid with 3 to 4 c.c. 



of concentrated hydrochloric acid. A beautiful 

 orange color denotes indoL 



3. If skatol is present, the same reagents produce a 



deep violet color upon heating. These tests 

 are very sensitive. 



4. The color formed with indol is only very slightly 



soluble in chloroform, while the color with 

 skatol is soluble in chloroform. 



Nelson, V. E., Jour. Biol. Chem., vol. xxiv, pp. 527-532, 1916. 



(B) I. Add I c.c. of a o.oi per cent, solution of potassium 



nitrite. 



2. Now add a few drops of sulphuric acid and warm 



in a water-bath. In the presence of indol a 

 pink color appears. 



3. If a solution containing skatol is treated with a 



few drops of nitric acid and a dilute solution of 

 potassium nitrite, a white turbidity is noted. 



(14) Millon's Reagent: 



Mercury metallic 5<^ gK^* 



Nitric acid (sp. gr. 1.42) 100 gm. 



Dissolve the mercury in its weight of concentrated 

 nitric acid and dilute with an equal volume of water. Only 



