36 MILK AND DAIRY PRODUCTS PART 



owners of cows as well as milk dealers, an estimation of the 

 percentage of fat in milk has become general. 



In the course of time a great number of different methods, of 

 varying value, have been proposed for determining the fat, 

 many of which have now only a historical interest or have 

 found no extensive application. It will therefore suffice here to 

 describe those which at the present time are in general use and 

 have been proved to give satisfactory results. The methods 

 for the estimation of fat may be divided, according to their 

 character and application, into two main groups : scientific 

 methods and practical methods. 



A. Scientific Methods. 

 1. Soxhlet's AT geometer Method. 



This method was worked out by Prof. Soxhlet of Munich l in 

 the year 1879, and for many years was the only one that gave 

 good results without having recourse to the gravimetric 

 methods of analysis which are so difficult to perform outside 

 the laboratory. The introduction of Soxhlet's method was the 

 consummation of long-continued attempts to provide an exact 

 and reliable method which could be used by anybody for 

 the estimation of fat. In actual dairy work the method has 

 now been replaced by others which need less sensitive appa- 

 ratus, but it is still used in many laboratories, although other 

 scientific methods will probably drive it from the field. 



Shortly, the principle of Soxhlet's method is the following : 

 When a measured amount of milk is mixed with certain quan- 

 tities of caustic potash solution and ether saturated with 

 water, there separates out afterwards an ethereal solution of 

 fat, in which all the fat of the milk is contained. 



If the specific gravity of the ether-fat solution is determined 

 by an araeometer, then the percentage of fat in the milk can be 

 obtained. As the difference between the specific gravities of 

 ether and fat is very great, small differences in the amount of 

 fat make a considerable alteration in the specific gravity of the 

 ether-fat mixture. The assumption of course has to be made 



1 Zeitschrift des landwirtsclmftlichen Vereins in Bayern, 1880, p. 659, and 

 1882, p. 18. 



