Rural School Lkaflet 



1231 



Fig. I.— Test 

 bottle 



into the l)oltle. Be sure to get ever}- drop of the milk, taking care to 

 drain the pipette and to blow the last drop into the bottle. A little 

 practice should make any one proficient with the j)ipette. 

 It is best always to make the test in duplicate; hence 

 two bottles are needed for each lot of milk. 



Using the acid. — The acid is very strong and must be 

 handled with great care. If any gets on the hands, face, or 

 clothing, it should be washed off quickly, and water should 

 always be ready for this purpose. Do not leave 

 the acid where children can get it. 



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 between 60° and 70° F. 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 will follow the glass surface to the bottom of 

 the bottle and form a layer under the milk. 



Hold the bottle by the neck and mix the contents with a 

 whirling motion for a few minutes, until no milk nor clear acid 

 is \nsible (Fig. 5). 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. 



Whirling the bottles. — The bottles are whirled in order 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 shoidd 

 have boiling water placed in them. 



Place the bottles in the machine so that each one 

 will have another directly opposite, in order to keep 

 the machine in Ijalance. Whirl the bottles for five 

 minutes at the proper speed for the machine in use 

 (Fig. 6). 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 the bottles for two more 

 minutes. Add enough hot water to bring the top of the fat 

 nearly to the top of the graduations on the neck of the 

 bottles. Whirl the bottles for another minute. The fat should 

 then form a clear column in the neck of the bottle. 

 Reading the percentage. — Keep the fat warrn so that it will be in a fluid 



l^ 



Fig. 2.— 



Pipette, 

 or milk 

 meastire 



Fig. 3.- 



Actd 

 measure 



