BUTTER 299 



soon the two liquids are completely separated, the 

 oil on top, the water at the bottom. If a little gum 

 were added to the water to make it sticky, the sepa- 

 ration of the oil would be less easily effected and the 

 mixture would retain its milky appearance for a 

 longer time; nevertheless the two liquids would al- 

 ways end by separating. 



"The fatty matter composing butter behaves in 

 the same way as the oil of our experiment. It is not 

 dissolved by the milk ; it is simply divided into very 

 minute particles that are held in place by a liquid 

 thickened with casein, just as water thickened with 

 gum holds for a long time the tiny drops of oil. Left 

 undisturbed long enough, these oily particles free 

 themselves and rise to the surf ace. " 



"Cream rises to the top of milk," observed Jules, 

 "just as oil that has been shaken up with water rises 

 to the surface; only the separation is slower on ac- 

 count of the casein that thickens the liquid." 



"That is the secret of this curious separation. 

 Milk is placed in large earthen nappies, smaller at 

 the bottom than at the top, and thus a large surface 

 is exposed to the cooling action of the air, which 

 hastens the separation of the cream. The full 

 nappy is put in a cool and very quiet place. In sum- 

 mer half a day is long enough for the rising of the 

 cream ; in winter it takes at least twenty-four hours. 

 When the separation is finished, the cream is re- 

 moved with a skimmer or a large almost flat spoon. 



"Cream is yellowish white, oily to the touch on 

 account of its greasy matter, and sweet and very 



