56 THE DAIRY OF THE FARM. 



ticulars must for the present suffice on the suhject of the 

 composition of milk. 



The preservation of milk in its natural composition, and 

 therefore in its sweetness, may he effected hy heating it in 

 "bottles or metallic vessels up to the boiling point, and then 

 closing them hermetically. The air is thus expelled to 

 which the chemical changes involved in the souring of 

 milk are due ; and, moreover, the curd which under the 

 influence of air acts as the disturbing ferment, loses for a 

 time, until again exposed to air,* its power of entering on 

 these chemical changes after being raised to the boiling 

 temperature. In this way milk is made capable of becom- 

 ing an article of commerce, and will be acceptable as a 

 drink after months of keeping. Condensed milk which is 

 milk subjected to evaporation so that more than one-half 

 of water is dissipated, and the whole reduced to a thickened 

 glutinous mass, to which in some cases sugar has been 

 added is now largely manufactured, and is especially 

 serviceable for use on shipboard, where it will keep fresh for 

 months. 



For the period during which milk is kept for the separa- 

 tion of its cream, its sweetness is to be maintained simply 

 by keeping it cool and in perfectly clean vessels and per- 

 fectly clean air. It is in this way that we avoid the opera- 

 tion of all external ferments, and hold in check the chemical 

 alterations which they promote, to which the souring and 

 other injurious changes in the condition of milk are due. 



The Dairy. In order to keep milk sweet, and for the 

 proper management of the processes which its manufactured 



* So that repeated heating of milk, nearly to the boiling point, at inter- 

 vals of 24 hours, or thereabouts, will keep it sweet, though it be exposed 

 to air during those intervals. 



