82 QUESTIONS AND ANSWERS 



sulphuric acid equal to the volume of milk taken. 

 Shake the bottle in a circle, but not sufficient to 

 mix the milk and acid to any great extent. In the 

 presence of formaldehyde a deep bluish-violet color- 

 ation appears in the circle where the milk and acid 

 join. Hydrochloric acid having a specific gravity 

 of 1.2 may be substituted for sulphuric acid in the 

 test. 



How may the presence of carbonates in milk be de- 

 tected? 



1. The ash of milk containing carbonates will 

 effervesce upon the addition of a few drops of 

 diluted hydrochloric acid. This is a strong indica- 

 tion of added carbonates. 



2. Add to lo or 15 c. c. of the milk an equal 

 volume of alcohol and a few drops of a i per cent 

 solution of rosalic acid. In the presence of car- 

 bonates a rose-red color appears, while pure milk 

 shows a light yellowish-red color. 



How may the presence of benzoic acid in milk be 

 detected ? 

 Add 5 c. c. of dilute hydrochloric acid to 50 c. c. 

 of the milk in a flask and shake to curdle. Extract 

 the curdled milk with successive portions of ether. 

 Transfer the ether to a separatory funnel and shake 

 with dilute ammonia, which separates the benzoic 

 acid from the fat, in the form of ammonium ben- 

 zoate. Draw off the ammoniacal solution and 

 evaporate in a dish over hot water until all free 

 ammonia has disappeared, but before dryness is 

 reached add a few drops of ferric chlorid reagent. 

 A flesh-colored precipitate indicates benzoic acid. 



