222 PHYSIOLOGICAL CHEMISTRY 



5. Pine Wood Test. Moisten a pine splinter with concentrated hydrochloric 

 acid and insert it into the material under examination. The wood assumes a 

 cherry-red color. 



6. Nitroso-indole Nitrate Test. Acidify some of the material under examina- 

 tion with nitric acid, add a few drops of a potassium nitrite solution and note the 

 production of a red precipitate of nitroso-indole nitrate. If the residue contains 

 but little indole simply a red coloration will result. Compare this result with the 

 result of the similar test on skatole. 



Tests for Skatole 



1. Better's Para-dimethylaminobenzaldehyde Reaction. 1 To 5 c.c. of the 

 distillate or aqueous solution under examination add i c.c. of an acid solution of 

 para-dimethylaminobenzaldehyde 2 and heat the mixture to boiling. A purplish- 

 blue coloration is produced 3 which may be intensified through the addition of a 

 few drops of concentrated hydrochloric acid. If the solution be cooled under 

 running water it loses its purplish tinge of color and becomes a definite blue. 

 The solution at this point may be somewhat opalescent through the separation of 

 uncombined para-dimethylaminobenzaldehyde. Care should be taken not to 

 add an excess of hydrochloric acid inasmuch as the end-reaction has a tendency 

 to fade under the influence of a high acidity. 



A rough idea regarding the actual quantity of skatole in a mixture may be 

 obtained by extracting this blue solution with chloroform and subsequently 

 comparing this chloroform solution, by means of a colorimeter (Duboscq), with 

 the maximal reaction, obtained with a skatole solution of known strength. 



2. Color Reaction with Hydrochloric Acid. Acidify some of the residue with 

 concentrated hydrochloric acid. Note the production of a violet color. 



3. Acidify some of the residue with nitric acid and add a few drops of a potas- 

 sium nitrite solution. Note the white turbidity. Compare this result with the 

 result of the similar test on indole. 



Tests for Phenol and Cresole 



1. Color Test. Test a little of the solution with Millon's reagent. A red 

 color results. Compare this test with the similar one under Tyrosine (see page 

 85). 



2. Ferric Chloride Test. Add a few drops of neutral ferric chloride solution 

 to a little of the material under examination. A dirty Wuish-gray color is formed. 



3. Formation of Bromine Compounds. Add some bromine water to a little 

 of the fluid under examination. Note the crystalline precipitate of tribrom- 

 phenol and tribromcresol. The reaction for phenol is as follows : 



Phenol. Tribromphenol. 



1 Herter: Bacterial Infections of the Digestive Tract, 1907, p. 141. 

 * Made by dissolving 5 grams of para-dimethylaminobenzaldehyde in 100 c.c. of 10 

 per cent sulphuric acid. 



If the color does not appear add more of the aldehyde solution! 



