QUALITATIVE EXAMINATION OF MILK. 



The analyst is seldom called upon to decide whether 

 the fluid under examination is really milk. If such a 

 case should arise, the essential constituents of the ma- 

 terial, namely, fat, casein, and milk sugar, should be isn- 

 lated. 



I. FATS. 



The fat may be extracted by one of the following 

 methods. By noting the appearance and properties of the 

 butter fat, an index may be had to the quality and source 

 of the milk in question. The ether solution of cows" 

 butter has a faint yellow color ; that of human colostrum 

 has an orange or ruby-red color (PfeifTer), while that 

 of goats' milk is colorless (Schaffer). The milky tur- 

 bidity of the fluid does not disappear by shaking with 

 ether. 



The exact composition of the butter fat in question 

 may be obtained by determining the volatile fatty-acids 

 according to Reichert's method, and the insoluble fatty- 

 acids by Hehner's method. The latter is based on the 

 fact that butter has about 87 per cent, of water-insoluble 

 fattj'-acids (varying between narrow limits according to 

 the time of year and the kind of food), while other animal 

 and plant fats contain from 92 per cent, to 95 per cent. 

 of these acids. The analysis, which requires about 200 

 cc. of milk, is carried out as follows: 



Of the previously weighed sample of butter, take 

 three or four grams by means of a glass rod and place 



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