Rural School Leaflet. 



933 



Fig. 51. — Putting the milk in- 

 to the test bottle. The pipette 

 is held at an angle with the 

 test bottle and its 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 

 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 (Fig. 52.) 

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

 due to the acid dissolving all the solid con- 

 stituents 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. 53). 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 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. 

 Read the mark or graduations at the extreme top 

 and bottom of the fat column. The difference 



Fig. 52. — Mixing milk and acid. 

 A rotary motion with the bottle 

 not pointed toward the face 



Fig. 53. — Whirling 

 the samples 



between these is the percentage of fat in the milk. 



