GASTRIC TESTS. 89 



ether, and distilling off the ether. The lactic acid remains. Dis- 

 solve in water, add a few drops of phenolphthalein as an indicator, 

 and see how much decinormal sodium hydrate (4 grammes per 

 liter) is necessary to neutralize it. Each cubic centimeter of the 

 alkali corresponds to 0.009 gramme of lactic acid. 



202. ARNOLD'S TEST FOR LACTIC ACID. Use the two 

 following solutions : 



No. 1. Saturated alcoholic solution of gentian-violet, 



0.2 cubic centimeter. 

 Distilled water, 500.0 cubic centimeters. 

 No. 2. Solution of ferric chlorid (U. S. P.), 5 cubic 



centimeters. 

 Distilled water, 20 cubic centimeters. 



In a porcelain dish place 1 cubic centimeter of No. 1 

 and add No. 2 until a bluish-violet color results. To this 

 add the filtered gastric juice. Lactic acid changes the color 

 to a green or greenish yellow. 



203.* To about 10 cubic centimeters of a 4-per-cent. 

 solution of carbolic acid (phenol) add a few drops of a 

 solution of ferric chlorid. Then dilute with water until 

 the color is amethyst or reddish-violet. Use this as a 

 reagent for the detection of lactic acid. The color is 

 changed to yellow by the lactic acid. 



204. Test 0.2-per-cent. hydrochloric acid in the same 

 way. The solution becomes colorless ; that is, hydrochloric 

 acid gives no color of its own, hence would not conceal the 

 lactic acid if both should be present. Try it. 



205. Test the lactic acid with a solution of ferric 

 chlorid so dilute that it is scarcely colored. The yellow 

 color is made stronger. 



206. Show that glucose or alcohol will give a yellow 

 color with the above reagents. (Experiments 203 and 

 205.) 



