EXAMINATION OF MILK. 



II. SEPARATION OF MILK INTO ITS CONSTITUENTS. 



Milk, diluted with water, precipitated with acetic 

 acid and filtered. 



I l -j 



Residue on filter (A) casein and Filtrate (B), albumin, milk-sugar, 



fat; extracted with ether. salts; evaporated at the boil- 



ing-point. 



Residue : casein Solution evapo- Coagulated albu- Evaporated f ur- 

 with some fat rated: butter- min (E). ther: calcium 



(C). fat(D). phosphate (F), 



milk-sugar (G) . 



Dilute 400 cc. of milk (whole milk) in a beaker with 1 liter 

 of water, and then add acetic acid, 1 cautiously with stirring, 

 until the casein separates in coarse flakes. An excess of acetic 

 acid is to be carefully avoided. The operation may be made 

 easier by taking out small amounts of the milk in a beaker, 

 adding acetic acid, and observing whether the casein becomes 

 more coarsely flocculent. The casein incloses the fat com- 

 pletely and carries it down with it. The action of the acetic 

 acid is to remove the alkali by means of which the casein is 

 dissolved in the milk. The mixture is filtered through mus- 

 lin, or the clear supernatant fluid is siphoned off and only the 

 residue filtered. 



The mixture (A) of casein and fat remaining on the filter 

 is washed once with water, drained, and the filter is lightly 

 .squeezed with the hand to remove the excess of wash-water. 

 It is then ground in a mortar with 100 cc. of absolute alco- 

 hol, which takes up the greater part of the water and some 

 of the fat, and, after standing for half an hour, filtered. The 

 alcohol is evaporated in a porcelain dish on the water-bath 

 and the dish with the residue set aside. To separate the 



1 Thirty per cent, acid, sp. gr. 1.041, is always understood by this term. 

 See table of reagents at the end of tho book. 



