348 THE ANALYSIS OF MILK AND MILK PRODUCTS. XV. 



increase in weight of the flask is taken as fat. The percentage 

 is then calculated, knowing that the weight in grammes of 

 milk taken = 5 x sp. gr. 



In this, as in all operations in which ether is employed, 

 great care should be taken to avoid ignition of the heavy ether 

 vapour. The most convenient condenser to use with the 

 Soxhlet extractor is the form consisting of two concentric 

 metal spheres, the inner one kept cool by a stream of cold 

 water and the vapour passed into the narrow space between 

 the spheres. This method of estimating fat is one of the most 

 accurate, especially if dry ether be used. 



2. Wenier-Schmicl method. This process, requiring only very 

 simple apparatus, is especially suited for sour milk. 10 c.c. of 

 the milk are placed in a large test tube (" boiling tube") or, 

 better, a 50 c.c. stoppered graduated test mixer ; 10 c.c. of 

 strong hydrochloric acid are added and the mixture shaken 

 and heated in a water bath for about 10 minutes until a brown 

 colouration is produced. The whole is then cooled and 30 c.c. 

 of water-saturated ether are added. The vessel is then closed, 

 vigorously shaken so as to dissolve the fat, and then allowed 

 to stand until the ether separates as a clear layer. The 

 volume of the ethereal layer is then read off and 10 c.c. are 

 withdrawn by means of a pipette, run into a small weighed 

 flask, the ether distilled off, the flask dried in a steam bath, 

 cooled, and weighed. The greatest drawback to this method 

 is the formation of a flocculent, semi-solid layer between the 

 clear ethereal and aqueous portions in the test mixer, which 

 renders the reading of the volume of the ether difficult. 



3. Rapid Centrifugal Volumetric Methods. Several 

 methods have been devised in which a measured quantity of 

 milk is treated with acids so as to dissolve the casein, &c., 

 heated, and subjected to centrifugal force so as to bring about 

 the separation of the fat in a fluid state, the volume of which 

 is then read off and thus its percentage amount. These 

 methods are very rapid, easy to carry out, and sufficiently 

 accurate for most purposes. The best known of the modern 

 methods are 



(a) The Lcffmann-Beam process. In this process the milk 



