176 DAIRY FARMING 



Making the Test. With the pipette add 17.6 c.c. of 

 cream to the cup, then with the same pipette add an equal 

 amount of water. Now slowly add of the tablet solution, 

 rotating the cup after each addition. As soon as a per- 

 manent pink color appears, the graduate is read and the 

 number of c.c. solution used will indicate the number of 

 hundredths of one per cent of acid in the cream. Thus, 

 if it required 50 c.c. of the tablet solution to neutralize the 

 cream then the amount of acid would be .50%. From 

 this it will be seen that with the Farrington test no calcu- 

 lation of any kind is necessary. 



CHURNING. 



Theory. Under the physical properties of butter fat 

 it was mentioned that this fat existed in milk in the form 

 of extremely minute globules, numbering about 100,000,- 

 ooo per drop of milk. In rich cream this number is in- 

 creased at least a dozen times owing to the concentration 

 of the fat globules during the separation of the milk. 



So long as milk and cream remain undisturbed, the fat 

 remains in this finely divided state without any tendency 

 whatever to flow together. This tendency of the globules 

 to remain separate was formerly ascribed to the supposed 

 presence of a membrane around each globule. Later re- 

 searches, however, have proven the falsity of this theory 

 and we know now that this condition of the fat is due 

 to the surface tension of the globules and to the dense 

 layer of casein that surrounds them. 



Any disturbance great enough to cause the globules to 

 break through this caseous layer and overcome their sur- 

 face tension will cause them to unite or coalesce, a process 

 which we call churning. In the churning of cream this 



