248 Testing Milk and Its Products. 



tincture; dry this on the water bath, cool and add a drop of 

 ammonia by means of a glass rod. A slaty blue color changing 

 to green is produced if borax is present. 1 



301. b. Bi-carbonate of soda. 100 cc. of milk to 

 which a few drops of alcohol are added, are evaporated 

 and carefully incinerated; the proportion of carbonic 

 acid in the ash as compared with that of milk of known 

 purity is determined. If an apparatus for the deter- 

 mination of carbonic acid is available, like the Scheibler 

 apparatus, etc., the per cent, of carbonic acid per gram 

 of ash (and quart of milk) can be easily ascertained. 

 Normal milk ash contains only a small amount of car- 

 bonic acid (less than 2 per cent.), presumably formed 

 from the citric acid of the milk in the process of incin- 

 eration. 



The following qualitative test is easily made: To 10 

 cc. of milk add 10 cc. of alcohol and a little of a one 

 per cent, rosolic-acid solution. Pure milk will give a 

 brownish yellow color; milk to which soda has been 

 added, a rose red color. A control experiment with 

 milk of known purity should be made. 



302. c. Fluorids. 100 cc. of milk are evaporated in 

 a platinum or lead crucible, and incinerated; the ash is 

 made strongly acid with concentrated sulfuric acid. If 

 fluorids are present hydrofluoric acid will be generated 

 on gentle heating and will be apparent from its etching 

 a watch glass placed over the crucible. 2 



303. d. Salicylic acid (salicylates, etc.}. 20 cc. of 

 milk are acidulated with sulfuric acid and shaken with 



1 See also 151. 



8 Chromates in dairy products may be readily determined by the use 

 of a silver-nitrate solution, see Molkerei-Ztg. (Berlin) 1899, p. 608. 



