144 BUTTER-MAKING. 
sionally it happens that a machine is run backwards. This is 
likely to cause the cover of the bowl to run off. 
Thickness of Cream.—The efficiency of skimming depends 
to some extent upon the thickness of the cream skimmed. 
Most separators, however, will skim within quite a wide range 
as to thickness. The richness of cream usually skimmed by 
separators is about from 25% to 50%. Most separators, how- 
ever, will do good skimming even if the cream contains as high 
as 60% fat. This, however, should be considered to be about the 
maximum, in order to get the best results from a separator. 
Slush in Bowl.—As has been mentioned before, there is 
always a thick, slimy substance which adheres to the bowl- 
wall. The composition of separator-slime is, according to 
Fleischmann, as follows: 
Watetinnts: .cc.ckiawehtaie aiigudeseenan OTsd 
Wass as oe ae SOS, 1.1 
Caseous matter. ..................2.2... 25.9 
Other organic substances................ 2.1 
AST pei Deir 2 deter ue 3.6 
100.0 
At the center of the bowl, or along the axis which runs 
perpendicular in the bowl, there is always considerable cream. 
It is practically impossible to get all the cream out of the bowl, 
even if it is flushed with much water. The amount of slush 
varies somewhat with the different kinds of separators. For 
this reason, it is essential that it should be taken into con- 
sideration when the comparative efficiency of skimming of 
different separators is considered. When the test extends over 
a comparatively long period, and the milk skimmed amounts 
to several thousand pounds, then the bowl-slush does not affect 
the conditions for comparative results very much; but when 
the test is short, and only a hundred pounds of milk, or a similar 
amount, is skimmed, then the amount of fat left in the bowl- 
slush will have considerable influence upon deciding which one 
is the most efficient machine. 
