VIl] 



B UTTER-MAKING 



117 



number of influences regulate the rate at which the 

 fatty globules separate themselves from the rest of 

 the milk by rising to the surface. What impedes the 

 separation is the fact that we have not in milk an 

 example of " pure emulsion," i.e. a mixture of a fat 



FIG. 16. DROP OF CREAM (diluted with water) five minutes after 

 churning has begun. (Kirchner.) 



with a liquid. The caseous matter in the milk is in 

 a semi-solid or colloidal form, as was pointed out in 

 a preceding Chapter, and this retards the separation 

 of the fat globules. The temperature of the milk is 

 another important factor. When warm milk is set 

 to cool, currents are set up, and it is difficult to 



