TESTING 331 



unites with all the milk substances except the fat and 

 generates much heat. 



311. Centrifuging. There are two machines in com- 

 mon use for centrifuging, one that runs by mechanical 

 power and the other smaller and runs by hand. If the 

 machine and atmosphere are very cold, the apparatus 

 can be warmed by placing hot water in it. This is not 

 necessary in a steam machine. In a factory where there 

 are a number, of samples to test, a power machine is usually 

 employed. In this machine there are pockets or cups in 

 which to set the test bottles. The machine or disk 

 must be balanced by placing bottles in opposite pockets. 

 These pockets are hinged so that when standing still the 

 bottle is in an upright position and when the centrifuge 

 is running, it is in a horizontal position. The machine 

 should then be covered and started running. It should 

 be run at the speed indicated. After five minutes, stop 

 the machine and fill the bottles with boiling water up to 

 the neck. This can be done without taking the bottles 

 out of the machine. A pipette or slender-spouted vessel 

 may be used to add the water. Whirl the bottles two 

 minutes, then add more boiling water to bring the fat 

 column into the graduated part of the neck of the bottle. 

 Then whirl one minute. The test should be read at once 

 or the bottles kept at a temperature of 130 to 140 F. until 

 ready to read. 



312. Reading the test. To read the test, subtract 

 the reading at the bottom of the fat column from that 

 at the highest point. The curved meniscus which always 

 forms at the top of the fat column should be included 

 in the reading. Duplicate samples should not vary more 

 than 0.2 of 1 per cent. Standard Babcock test bottles 

 and pipettes should always be used. In some states the 



