SEPARATION OF CREAM. 127 
their surface tension when the temperature is lowered. Owing 
to this increase in surface tension, the liquid drops unite together 
at a low temperature much more rapidly than they do at a 
high temperature. For instance, two drops of molten iron 
unite much more readily just previous to solidifying than 
they do while the temperature is higher, and the liquid more 
fluid. As the fat in milk is present in the form of small liquid 
globules, as mentioned previously, it seems probable that 
these fat-globules might have properties similar to those of 
the liquid mentioned above, and behave similarly in the milk, 
when set at low temperatures, in accordance with the deep 
setting method. If the fat-globules act in accordance with 
this theory, it seems probable that there is no real membrane, 
other than that resulting from surface tension, enveloping 
each fat-globule. If there were such a membrane, composed 
of albuminoid chiefly, then undoubtedly the fat-globules would 
not assume this property. 
With such a deep layer of milk the lower most fat-globules 
must evidently encounter a great many other globules as 
they rise. If the physical force mentioned does not facilitate 
the process of uniting the globules, they would partly unite 
without it. The more they unite in small bunches, or masses, 
the greater would be the tendency for them to rise, as explained 
previously, and more of the smaller fat-globules would be 
carried along. The bottom globules would tend to partly 
unite and form a filter, which passes up through the milk 
by the buoyant force, or force of levity. 
If this latter explanation holds true, then more of the milk 
constituents would be present in the cream from the deep- 
setting system than in the cream from the shallow-pan system. 
By comparing the cream raised by the shallow-pan system 
with that raised by the deep-setting system, before the cream 
has been removed from the milk, it will be noticed that the 
cream raised by the shallow-pan system appears to be much 
yellower than is that raised by the deep-setting system. This 
condition can only be due to the fact that the surface cream, 
