10 SELLING MILK 
taining 4 per cent butter fat, the dairyman ex- 
pects to receive the full market price for milk 
and a premium or extra price for butter fat equal 
to the value of the I per cent excess which his 
milk contains. 
Butter fat is measured best by the Babcock 
test. Sulphuric acid added to milk makes the 
separation of butter fat easy when the mixture 
is whirled in a centrifugal machine. The sepa- 
rated fat appears as yellow oil in the neck of 
the glass bottle and the quantity can be easily 
read from graduated marks on the neck. 
Fat tests may be made weekly or monthly. 
Disputes often occur between farmers and dealers 
regarding the fat tests. Changing cows changes 
the amount of fat in the mixed milk of the dairy. 
Removing cream from the top of the can for the 
house makes a big difference in the fat test of the 
the milk on that day. Where the farmer is 
honest, and the dealer is honest, disputes can 
always be settled by having the fat test made 
in the presence of both parties. 
