44 ANALYTICAL PROCESSES. 



lo c. c. of the milk are mixed with an equal volume 

 of alcohol, and a few drops of a one per cent, solution 

 of rosolic acid added. Pure milk shows merely a 

 brownish-yellow color, but in the presence of sodium 

 carbonate a more or less marked rose-red appears. 

 The delicacy of the test is enhanced by making a 

 comparison cylinder with the same amount of milk 

 known to be pure. Any considerable addition of the 

 salt may be detected by the increase in the ash, its 

 marked alkalinity and effervescence with acid. 



Benzoic Acid — 250-500 c. c. of the sample are 

 rendered alkaline by a few drops of calcium or barium 

 hydroxid, evaporated to one-fourth bulk, mixed with 

 sufficient calcium sulfate to make a pasty mass and 

 dried on the water bath. When condensed milk is 

 examined, 100-150 grams should be mixed directly 

 with sufficient calcium sulfate, and a few drops of 

 barium hydroxid. Since the calcium sulfate is only 

 employed to facilitate the drying, it may be replaced 

 by powdered pumice or other inert material. The dry 

 mass is finely powered, moistened with dilute sul- 

 furic acid and then exhausted three or four times 

 with about twice its volume of cold (50 per cent.) alco- 

 hol, which dissolves benzoic acid freely, but only mere 

 traces of the fat. The alcoholic liquid which, in ad- 

 dition to the benzoic acid, contains milk sugar and 

 mineral matter, is mixed thoroughly, neutralized with 

 barium hydroxid and evaporated to small volume. The 

 residue is acidified with weak sulfuric acid and extract- 

 ed with successive small portions of ether. On evap- 



