64 A UXIT IN AGRICULTURE 



the milk and suck up the milk above the 17.6 c.c. mark. Quickly put 

 the index finger over the upper end of the pipette; and, by releasing 

 the pressure, allow the milk to run out until its upper surface is even 

 with 17.6 c.c. mark when the pipette is held straight up and down. 



Place the point of the pipette a short distance into the test-bottle 

 neck, holding it against the glass and with both pipette and bottle at 

 an angle. Remove the finger to allow the milk to flow into the bottle. 

 Be sure to get every drop of the milk, taking care to drain the pipette 

 and to blow the last drop into the bottle. 



After all the samples of milk to be tested have been measured, 

 the acid should be added. Fill the acid measure to the 17.5 c.c. mark 

 with acid that is neither very cold nor very hot. Pour this into the 

 bottle with the milk, holding the bottle in a slanting position. The 

 acid will then carry down any milk left in the neck, follow the glass 

 surface to the bottom of the bottle and form a layer under the milk. 



Hold the bottle by the neck and give it a circular motion for a 

 few minutes, mixing the milk and acid until no milk or clear acid is 

 visible. By this time the contents will be dark colored and hot. This 

 change is due to the acid dissolving all the solid constituents of the 

 milk except the fat, which it does not affect. 



Place the bottles in the machine so that each one will have an- 

 other directly opposite, to keep the machine in balance. Whirl the 

 bottles five minutes at the proper speed for the machine in use. Then 

 stop it; and, with the pipette or other convenient means, add hot 

 water to each bottle until the contents come up to the bottom of the 

 neck. Whirl two minutes. Add hot water enough to bring the top of 

 the fat nearly to the top of the graduations on the neck of the bottles. 

 Whirl one minute. The fat should then form a clear column in the 

 neck of the bottle. 



Reading iJie Percentage. Keep the fat warm so that it will be 

 in the fluid condition. Hold the bottle by the upper end of the neck, 

 letting it hang in a perpendicular position on the level with the eye. 

 Read the graduations at the extreme top and bottom of the fat column. 

 The difference between these is the percentage of fat in the milk. 



