2l8 PHYSIOLOGICAL CHEMISTRY 



TESTS FOR VARIOUS PUTREFACTION PRODUCTS 



Tests for Indole 



The various tests for indole ond skatole may be carried out upon an 

 aqueous solution ot these products or upon an aqueous solution of 

 the residue from Ether Extract No. 2 (see page 172). A distillate 

 secured by distilling a putrefaction mixture first in alkaline and then 

 in acid reaction may also be employed. 



1. Herter's /3-Naphthaquinone Reaction. (a) To a dilute aqueous solution 

 of indole (i : 500,000) add i drop of a 2 per cent solution of /3-naphthaquinone- 

 sodium-monosulphonate. No reaction occurs. Add a drop of a 10 per cent 

 solution of potassium hydroxide and note the gradual development of a blue 

 or blue-green color which fades to green if an excess of the alkali is added. 

 Render the green or blue-green solution acid and note the appearance of a 

 pink color. Heat facilitates the development of the color reaction. 



One part of indole in one million parts of water may be detected by means of 

 this test if carefully performed. 



(b) If the alkali be added to a more concentrated indole solution before the 

 the introduction of the naphthaquinone the course of the reaction is different, 

 particularly if the indole solution is somewhat more concentrated than that men- 

 tioned above and if heat is used. Under these conditions the blue indole com- 

 pound ultimately forms as fine acicular crystals which rise to the surface. 



If we do not wait for the production of the crystalline body but as soon as the 

 blue color forms, shake the aqueous solution with chloroform, the blue color dis- 

 appears from the solution and the chloroform assumes a pinkish-red hue. 

 This is a distinguishing feature of the indole reaction and facilitates the differen- 

 tiation of indole from other bodies which yield a similar blue color. A very sat- 

 isfactory method for the quantitative determination of indole is based upon the 

 principle underlying this test (see chapter on Feces). 



2. Formaldehyde Reaction (Konto). To i c.c. of the material under exami- 

 nation in a test-tube add 3 drops of a 40 per cent solution of formaldehyde and i 

 c.c. of concentrated sulphuric acid. Now agitate the mixture and note the appear- 

 ance of a violet-red color if a trace of indole is present. The test is said to serve 

 for the detection of indole when present in a dilution of i : 700,000. 



Skatole gives a yellow or brown color under the above conditions. 



3. Cholera-red Reaction. To a little of the material under examination in a 

 test-tube add one-tenth its volume of a 0.02 per cent solution of potassium nitrite 

 and mix thoroughly. Carefully run concentrated sulphuric acid down the side 

 of the tube so that it forms a layer at the bottom. Note the purple color. Neu- 

 tralize with potassium hydroxide and observe the production of a bluish-green 

 color. 



4. Nitroprusside Reaction (Legal). To a small amount of the material under 

 examination in a test-tube add a few drops of a freshly prepared solution of sodium 

 nitroprusside, Na 2 Fe(CN) 5 NO+ 2H 2 0. Render alkaline with potassium hydroxide 

 and note the production of a violet color. If the solution is now acidified with 

 glacial acetic acid the violet is transformed into a blue. 



