152 THE BABCOCK TEST 



it a gentle rotary motion. The mouth of the bottle must never 

 be covered while mixing. The action of the acid on the water 

 of the milk causes a rapid change in temperature, heating the 

 mixture to a high degree and at the same time dissolving all 

 the non-fatty solids of the milk and making possible a rapid 

 and complete separation of the fats. 



^VHIRLING THE BOTTLES 



The test bottle and contents should now be placed in a 

 special machine and whirled at a high speed. The bottles 

 assume a horizontal position as the machine reaches the re- 

 quired speed, and as the fats are the lightest part of the milk, 

 they will gather in a layer on the surface of the liquid nearest 

 the center of the machine. Although the principle is the same 

 in all machines used for whirling bottles, there are several 

 types and sizes adapted for different requirements. The 

 power machines (Figures 11 and 12) are usually used in cream- 

 eries and wherever steam is available. 



The required speed of the machine will necessarily depend 

 upon the diameter of the revolving bottle carrier.^ For the 

 power machines a speed indicator is necessary, but the opera- 

 tor of the hand machin<j can note the number of revolutions of 

 the bottle carrier to one revolution of the crank and govern his 

 speed accordingly. With the hand machine full speed should 

 be maintained for seven minutes for the first whirling, after 

 which the bottles should be placed in boiling water to keep the 

 contents hot, and enough hot water should be added to the 

 contents of the bottle to bring the liquid to the base of the 

 neck, or even up to the zero mark. The bottles are now re- 

 placed in the machine and whirled again at full speed for three 

 minutes. The fats will collect at the base of the neck during 

 the second whirling, and after the machine is at a standstill 

 enouoh hot water should be added to float the fat within the 

 limits of the graduated scale on the neck of the test bottle. 

 The bottles are again whirled for two minutes at full speed, 

 after which they should be placed in a basin of water hot 



tA bottle carrier fifteen inches in diameter should be made to revolve 1,000 

 times per minute. 



