SEPARATION OF CREAM. 125 



and keep the milk in good condition. In many parts of the 

 eastern United States, the deep-setting system is in general 

 use. A special form of can is used. The can is simply an 

 ordinary four-gallon can, about 8 inches in diameter and 20 

 inches deep. It has a glass on one side near the bottom or near 

 the top, which allows the reading of the thickness of the layer 

 of cream. On each side of the glass is a graduated scale, which 

 gives the reading in inches. In case the cream is being sold 

 to a creamery, the hauler comes along, notes the depth of the 

 layer of cream, and records the number of inches of cream 

 opposite the patron's name. At the end of the month, or 

 whenever the time for payment comes, the money is appor- 

 tioned according to the number of inches of cream delivered 

 by each of the patrons. No test for fat is made. This is what 

 is known as the "Cooley system," and is used quite extensively 

 in the East, especially in Massachusetts. 



While cream usually arrives at the creamery in a fair con- 

 dition, there is the objection that the cream is always thin. It 

 seldom contains any more than 18 or 20% of fat. 



No good explanation has yet been given why cream in a 

 deep layer of milk at 40° F. should rise more quickly and more 

 completely than in a thin layer at a higher temperature. 

 * Arnold seeks to explain it by saying: "Water is a better 

 conductor of heat than fat; hence when the temperature of 

 the milk varies either up or down, the water in the milk feels 

 the effect of the heat or cold 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." 



This explanation is, according to Babcock,t not satisfactory. 

 He says: " Though it is true that water is a better conductor 

 of heat than fat, the small size of the fat-globules renders it 



* American Dairying, p. 210. 



t Wisconsin Experiment Station, Bull, 18, p. 24. 



