XVI. 



THE ANALYSIS OF MILK AND MILK PRODUCTS 



349 



2. Werner -Schmid method. This process, requiring 

 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 milk 

 mixer ; 10 c.c. of strong hydrochloric acid 

 are added and the mixture shaken and heated 

 in a water bath for about ten 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 are withdrawn by means of a pipette, run 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 dis- 

 tilled off, the flask dried in a steam bath, 

 cooled and weighed. The greatest draw- 

 back 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 Me- 

 thods. Several methods have been devised 

 in which a measured quantity of milk is 

 treated with acids so as to dissolve the 

 casein, etc., heated, and subjected to centri- 

 fugal force so as to bring about the separa- 

 tion of the fat in a fluid state ; the volume 

 of the fat is then read off and gives directly 

 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 Leffmann-Beam process. In this 

 process the milk is mixed with a small quan- 

 tity of a mixture of amyl alcohol, C 5 H U OH, 

 and hydrochloric acid, whereby the casein is 

 coagulated. Strong sulphuric acid is ibhen 

 added, in which the casein dissolves, the 

 whole liquid becoming hot from the action 

 of the sulphuric acid upon the water. The 

 amyl alcohol aids in the separation of the fat, clenser - 

 most probably because it is a common solvent 



for fat and the acid liquor. The emulsified a nd the glass bulb as core, 

 fat thus speedily separates and by centri- 

 fugal action forms a distinct and clear layer a metal water bath - 

 above the acid liquor, which usually takes a dark purple colour. 



very 



FIG. 14. Adams's paper-coil 

 method. 



A is a pipette which acts 

 as a condenser to the ether 



densation in B. 



B is the metal ball con- 



D is the weighed flask, in 



The 



