TESTING FOR BUTTERFAT 617 



is advisable to add the acid in about three installments, shaking the 

 bottle after each addition. Attention to this precaution helps to 

 secure clear tests. 



WhirEng and Adding Water. Set the test bottles into the 

 Babcock centrifuge. If the test bottles containing the mixture 

 of milk and acid are held over and allowed to become cool, they 

 should be heated by setting in hot water before whirling. 



Steam turbine and electric driven testers with not less than 

 twenty-four pockets are best adapted for factory use. They are 

 constructed of two general sizes, those having a twelve-inch diame- 

 ter wheel and those having an eighteen-inch diameter wheel. 



Table 104. Correct Speed of Testers of Different Diameters 1 

 Measuring from Pocket Bottom to Opposite Pocket Bottom 



Diameter of Wheel Revolutions of. Wheel 



Inches per Minute 



10 1,074 



12 980 



14 909 



16 848 



18 800 



20 759 



22 724 



24 693 



Fill the bottles to the bottom of the neck with hot, soft water; 

 whirl again for two minutes and fill the bottles with hot, soft water 

 to about the 7 per cent mark ; whirl for one minute. The tempera- 

 ture of the water added should be not lower than 140 degrees F. and 

 preferably near that of boiling water (212 degrees F). 



Reading the Test. Place the test bottles in a water bath and 

 read after a temperature of 130 F. to 140 F. has been maintained 

 for not less than three minutes. Measure the fat column with a 

 pair of dividers, including the meniscus or curve, both at the bottom 

 and at the top of the fat column. Each subdivision represents .1 

 per cent ; each main division represents 1 per cent. Record the per- 

 centage of fat thus found on the test sheet. 



Abnormal Appearance of the Fat Column. When the test is 

 made properly and in accordance with above directions, the fat 



Farrington & Woll, Testing Milk and Its Products. 



