208 MILK HYGIENE 



The addition of water causes a lower specific gravity 

 of the whey. In the examination of adulterated 

 skimmed milk, he found the figures to be 1.0256, 1.0246, 

 1.0254 and 1.0257 (rennet method) and 1.0242, 1.0234, 

 1.0238 and 1.0241 (acid method). 



e. The determination of the fat content of milk. There 

 are many methods for determining the fat content of 

 milk; some of these are too inexact to be considered 

 (e.g., the above mentioned transparency test by means 

 of the lactoscope, and the like), others give very good 

 results but require rather expensive apparatus, still 

 others require exact weighings and work that can be 

 done only in chemical laboratories. Some simple tests 

 are, however, so accurate and so practical that they are 

 available for the work of milk inspection. 



Among the methods used, besides the transparency 

 test already mentioned, the creamometer should be 

 named, that is, the measurement of the layer of cream 

 which rises when the milk is allowed to stand. Since, 

 however, the thickness of the layer of cream furnishes 

 no reliable gauge as to the fat content, this method can- 

 not be used if there is to be a prosecution. The separa- 

 tion of the cream by a centrifuge of high velocity 

 (Fjord 's test), and subsequently measuring the layer of 

 cream, gives better results and is often used in cream- 

 eries for comparing milks. For general use, however, 

 it is impractical, and not sufficiently accurate. 



The available methods are, principally, Soxhlet's 

 method, which was formerly used to a greater extent 

 than it is now; Gerber's method, [the Leffmann-Beam 

 and the Babcock methods] and methods of chemical 

 analysis. 



Soxhlet's method is founded upon the following prin- 

 ciple : the solution of the fat in ether and the determina- 

 tion of the specific gravity of this solution. 



