CHAPTER III 

 CHEMICAL EXAMINATION 



ALTHOUGH the extent of the chemical examination of milk 

 required in public health work is usually confined to the deter- 

 mination of the fat and total solids and the detection of pre- 

 servatives, a brief description of reliable methods for the esti- 

 mation of other constituents will also be given in this chapter 

 as they are invaluable for the correct diagnosis of sophistication. 



As the great majority of ordinances and statutes regulating 

 the sale of milk contain no reference to constituents other than 

 fat and total solids, these will be considered first. 



Estimation of Fat. The various methods introduced for 

 the determination of fat in milk may be divided into three 

 groups. 



(1) Volumetric estimation of the fat brought to the surface 

 by centrifugal force after liberation by the addition of chemicals. 



(2) Ethereal extraction of the fat liberated by the addition 

 of chemicals. 



(3) Ethereal extraction of the dried milk. 



The methods which comprise the second group, though 

 invaluable for dealing with milk products, are not in general 

 use for the examination of fresh milk and will not be given in 

 detail. 



The mechanical methods of group one are now in almost 

 universal use and are capable, in practised hands, of yielding 

 accurate results. The three chief mechanical methods are the 

 Leffmann-Beam, Babcock, and Gerber. In England, the Leff- 

 man-Beam and the Gerber are almost exclusively used whilst 

 in America, although both the Babcock and Gerber processes 

 are official, the former is more generally employed. 



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