88 BRITISH DAIRYING. 



remain undisturbed, in order that as much of the cream as may 

 be so inclined will succeed in reaching the surface. The 

 open-pan system of cream-raising, the Jersey, the Cooley, the 

 Swartz, and all other pans or cans as well, do not therefore pro- 

 vide us with the best way of extracting a maximum proportion 

 of the cream from milk. 



It has been reserved to men of our own day to invent a 

 machine, the Separator, which leaves behind in the milk less 

 than one twentieth of i per cent, of the cream, whereas by 

 skimming at the very least three-quarters of i per cent, remain 

 in the milk, and generally a great deal more. In other words : 

 skimming leaves behind in the milk at least fifteen times as 

 much butter as separating does, simply because all the cream 

 does not rise to the surface, and therefore cannot be skimmed. 



But there is at all events a way in which the rising of cream 

 may be hastened in pans and cans, and the principle has been 

 adopted in the Jersey and other " creamers " I have mentioned. 

 The late Professor Arnold, of America, told us what the prin- 

 ciple is in the following words : " Water is a better conductor 

 of heat than fat : hence, when the temperature of milk varies up 

 or down, the water in the milk feels the effect of heat or cold 

 a little sooner than the fat in the cream does ; therefore the 

 cream is always a little behind the water in swelling with heat 

 or shrinking with cold thus diminishing the difference between 

 the specific gravity of the milk and cream when the temperature 

 is rising, and increasing it when the temperature is falling? 

 Therefore it follows that when warm milk in a can is placed in 

 a bath of cold water whose temperature is 40 or less, the 

 cream rises pretty quickly while the temperature of the milk is 

 falling to that of the water. 



Under this system of a falling temperature all the cream that 

 is inclined to rise has reached the upper layer of milk in about 

 twelve hours, or less ; but though the milk has fallen to the 

 temperature of the water in much less than twelve hours, the 

 cream cannot keep pace with it, and continues to rise when the 

 temperature is stationary. A slowly-falling temperature is con- 

 sidered the best after all, especially in the open -pan system ; 



