THE CARE OF MlLK. ^35 



for small dairies where no more than ten or twenty cows 

 are kept. Cream is lighter than milk, and according to 

 the rules of gravity the former will rise through and 

 float upon the latter. But there are some conditions 

 which control and regulate this movement. The relative 

 densities of the two fluids are changed by differences of 

 temperature. Warm milk is lighter for the same bulk 

 than cold, because cold condenses it ; and a cubic foot 

 or a measured gallon of milk at forty-five degrees is 

 heavier than the same bulk at sixty-five degrees. But 

 the gravity of the cream is not changed to so great an 

 extent as that of the milk is, and the cream becomes 

 relatively lighter under these circumstances, and conse- 

 quently rises to the surface more rapidly. This is the 

 principle upon which the Swedish dairymen have prac- 

 ticed their deep pail and cold water system of setting 

 milk ; and this system has been adopted by American 

 dairymen with much success. It may be applied to 

 either deep or shallow pans, or to the earthen pans, a 

 sort of intermediate compromise between the two, in com- 

 mon use in the Eastern Pennsylvania dairies, and also in 

 Holland. In these dairies running spring water is used 

 for cooling the milk, but the temperature is not below 

 fifty-five or sixty degrees in summer, and the earthen 

 pans are not over eight inches deep. It is necessary to 

 use pans of this or even less depths when the tempera- 

 ture is not less than sixty degrees, because otherwise the 

 cream would not have time to rise before the milk be- 

 came sour and thick. But in the twent3Mnch deep 

 pails set in ice- water at a temperature of forty-five 

 degrees the milk will remain sweet for seventy-two 

 hours, and all the cream will rise in twelve liours. But 

 this rapid separation of the dream has another effect 

 which should be mentioned, and this is that as the 

 cream rises it carries with it by attraction and between 

 the globular particles a considerable quantity of the 



