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 fcels 
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, 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. 
{ Wisconsin Experiment Station, Bull. 18, p. 24. 
