690 



Rural School Leaflet. 



Fig. 29. — Putting the milk in- 

 to the test buttle. The pipette 

 is held at an angle with the 

 test bottle audits point against 

 the inside of the neck. 



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 cc mark with acid that is neither very 

 cold nor 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 and follow the 

 glass surface to the bottom of the bottle and 



give 



Fig. 30. — Mixing milk and 

 aeid. A rotwy motion zvitli 

 the bottle not pointed toivard 

 the face. 



form a layer under the milk. 



Hold the bottle by the neck and 

 it a circular motion for a few minutes, 



mixing the milk and acid until no milk or clear acid is visible (Fig 30). 



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



due to the acid dissolving all the solid con- 



stitutents of the milk except the fat, which 



it does not affect. 



Whirling the bottles. — The bottles are 



whirled to separate the fat so that it can be 



measured. They should be hot when 



whirled. If necessary they may be heated 



by standing in hot water before being put 



into the machine. A steam machine is 



easily kept hot when in use. Other kinds 



should have boiling hot water placed in 



them. 



Place the bottles in the machine so that each one will have another 



directly opposite, to keep the machine in balance. Whirl the bottles five 



minutes at the proper speed for the machine in use (Fig. 31). Then stf^p 



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. \\'hirl 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 the percentage. — Keep the fat warm so 

 that it will be in a 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. 

 Pcad the mark or graduations at the extreme top 

 and bottom of the fat column. The difference 

 between these is the percentage of fat in the milk. 



Fig. 31. — Whirling 

 the samples. 



