I 56 PHYSIOLOGICAL CHEMISTRY. 



wash it with water. Remove the precipitate to a small porcelain 

 dish, add 3 c.c. of an acid-alcohol mixture 1 and a few drops of a 

 dilute solution of sodium nitrite and heat. The production of a 

 green color indicates the presence of bile pigments. 



5. Tests for Bile Acids, (a) Pettenkofer's Test. To 5 c.c. 

 of diluted bile in a test-tube add 5 drops of a 5 per cent solution 

 of sucrose. Now run about 2-3 c.c. of concentrated sulphuric 

 acid carefully down the side of the tube and note the red ring at the 

 point of contact. Upon slightly agitating the contents of the tube 

 the whole solution gradually assumes a reddish color. As the 

 tube becomes warm, it should be cooled in running water in order 

 that the temperature of the solution may not rise above 70 C. 



(b) Mylius's Modification of Pettenkofer's Test. To approxi- 

 mately 5 c.c. of diluted bile in a test-tube add 3 drops of a very 

 dilute (i : 1,000) aqueous solution of furfurol, 



HC-CH 

 HC C-CHO. 



y 



Now run about 2-3 c.c. of concentrated sulphuric acid carefully 

 down the side of the tube and note the red ring as above. In this 

 case also, upon shaking the tube the whole solution is colored red. 

 Keep the temperature of the solution below 70 C. as before. 



(c) Neukomm's Modification of Pettenkofer's Test. To a few 

 drops of diluted bile in an evaporating dish add a trace of a dilute 

 sucrose solution and one or more drops of dilute sulphuric acid. 

 Evaporate on a water-bath and note the development of a violet 

 color at the edge of the evaporating mixture. Discontinue the 

 evaporation as soon as the color is observed. 



(d) v. Udrdnsky's Test. To 5 c.c. of diluted bile in a test-tube 

 add 3-4 drops of a very dilute (i :i,ooo) aqueous solution of fur- 

 furol. Place the thumb over the top of the tube and shake the 

 tube until a thick foam is formed. By means of a small pipette 

 add 2-3 drops of concentrated sulphuric acid, to the foam and note 

 the dark pink coloration produced. ^ 



(e) Guerin's Reaction. To equal volumes of diluted bile and 

 alcohol in a test-tube add 5-6 drops of a saturated aqueous solution 



1 Made by adding 5 c.c. of concentrated hydrochloric acid to 95 c.c. of 96 per 

 cent alcohol. 



