224 BUTTER. 



571. The sugar of milk, when pure, cannot under- 

 go the alcoholic fermentation ; but by certain means 

 it may be modified and converted into grape sugar, 

 which can ferment. The Tartars, by causing milk 

 to undergo the alcoholic fermentation, prepare an 

 intoxicating drink which contains alcohol. 



572. An imperial gallon of fresh cow's milk, con- 

 tains about one pound seven ounces of solid matter. 

 Of this five ounces are fat, nearly eight ounces case- 

 ine, and about seven ounces sugar. The saline mat- 

 ters present in the milk include about eighteen grains 

 of common salt, and one hundred and sixty grains 

 of phosphate of lime. 



573. Milk derives its opaque white appearance 

 from the presence of innumerable minute globules of 

 fatty matter, which are suspended throughout it ; it is, 

 in fact, a natural emulsion, or a solution holding par- 

 ticles of oil in suspension. 



574. Cream, or the lighter part of milk, consists 

 principally of these minute globules, or drops of oil, 

 separated from each other by the solution of caseine, 

 &c., in which they float ; being lighter than water, 

 they rise to the surface, when fresh milk is allowed 

 to stand. The operation of churning consists merely 

 in agitating the cream, under the influence of a mode- 

 rate degree of warmth; the particles of oil then 

 unite and collect together in masses, forming butter. 



575. It is difficult to remove the whole of the 

 caseine from butter, and its presence is highly objec- 

 tionable from its great proneness to putrefy ; by care- 



