CHAPTEK VIII. 



THE ESTIMATION OF FAT. 



MORE attention has perhaps been paid to the estimation of fat 

 in milk than that of any other constituent. The methods are 

 very numerous, and may be divided conveniently into three 



(1) Gravimetric methods, in which the fat is separated from 

 the milk by a suitable solvent, and weighed after evaporation of 

 the solvent. 



(2) Volumetric methods, in which the fat is separated from 

 the milk by suitable means, and its volume measured. 



(3) Indirect methods, in which the amount of fat is deduced 

 from the determination of some physical property. 



Of these methods the gravimetric methods are undoubtedly 

 the most accurate, though they are all to a certain extent tedious 

 and not capable of use by unskilled persons. 

 , The solvent chiefly used for extracting the fat is ether, which 

 is convenient on account of the low boiling point and heat of 

 volatilisation, its great solvent power for fat, and its compara- 

 tively great miscibility with water, which renders it unnecessary 

 to have the milk solids in a state of absolute dryness. 



Petroleum ether, chloroform, carbon disulphide, benzene, 

 carbon tetrachloride, and amyl alcohol have also been used, but, 

 though they give the same results, are not so convenient. 



Gravimetric Methods. 



The leading gravimetric methods are discussed in the following 

 pages ; on the whole the Gottlieb method is the best, though 

 those due to Adams, Storch, Werner-Schmid, and Bell are little, 

 if at all, inferior in accuracy. 



The Adams Method. Dr. M. A. Adams, Public Analyst 

 for Kent, was led to devise this method from his observation 

 that when milk was dropped on blotting-paper, it spread out to 

 a much greater extent than was possible in a basin, flask, or 

 even on a flat surface of glass ; he was of opinion that extraction 

 of fat by ether would be much more complete. 



115 



