230 Testing Milk and Its Products. 



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. 



293. c. Fluroids. 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. 1 



294. d. Salicylic acid (salicylates, etc.). 20 cc. of milk 

 are acidulated with sulfuric acid and shaken with ether; 

 the ether solution is evaporated, and the residue treated 

 with alcohol and a little iron-chlorid solution; a deep 

 violet color will be obtained in the presence of salicylic 

 acid. 



295. e. Formalin, (a forty-per cent, solution of formal- 

 dehyde in water). A solution of diphenylarnin is made 

 with water and just enough sulfuric acid to dissolve it. 

 The milk to be tested, or better, the distillate therefrom, 

 is added to this solution and boiled. If formalin be pres- 

 ent, a white flocculent precipitate is formed; if the acid 

 used contained nitrates, a green precipitate will be 

 formed. 



The following method by Hehner is stated to show the 

 presence of 1 part of formaldehyde in 200, 000 parts of 

 milk : the milk is diluted with an equal volume of water, 



i Chromates in dairy products may be readily determined by the use of 

 a silver-nitrate solution, see Molkerei Ztg. (Berlin) 1899, p. 603. 



