346 THE HANDBOOK FOR PKACTICAL FARMERS 



upon the percentage of fat, will be required for a nine-gram 

 charge. After adding the acid to the cream, the procedure up to 

 the reading of the percentage is exactly the same as in the milk 

 test. After the final whirling, the test bottles are submerged to 

 a point above the fat column in water at one hundred and thirty- 

 five degrees to one hundred and forty degrees F. in a suitable 

 tank. After remaining in the tank for about fifteen minutes 

 they are removed and the readings quickly made. The impor- 

 tant difference between reading the cream test and the milk test 

 is that in the cream test the fat column included is from the bot- 

 tom of the lower meniscus to the bottom, not the top, of the 

 upper meniscus. 



Some operators prefer to destroy the upper meniscus by 

 dropping into the bottle at this point a few drops of a liquid in 

 which the fat is not soluble. Glymol (petrolatum liquidum, 

 U. S. P.), known commercially as white mineral oil, gives satis- 

 factory results and may be purchased at almost any drug store. 

 If the fat column is read with the upper meniscus intact, care 

 must be taken that the eye is on a level with the points on the 

 scale at which the readings are made; otherwise an error will 

 be introduced. 



TESTING SKIM MILK FOR FAT 



In general skim milk is tested Avith the Babcock test in the 

 same manner as w^hole milk, but the test does not apply to it 

 with the same degree of accuracy. The reason for this is per- 

 haps as follows : The fat in milk, as already shown, exists as 

 fat globules of different sizes. In the process of skimming, 

 either by the centrifugal separator or by gravity, the force tend- 

 ing to separate the fat from the other milk constituents acts 

 more strongly upon the larger globules ; consequently^ there is a 

 much larger proportion of small globules in skim milk than in 

 the Avhole milk. In the Babcock test the fat is driven into the 

 neck of the test bottle by centrifugal force. Here again the force 

 acts more strongly upon the larger globules. Some of the 

 smaller globules never reach the neck of the test bottle. This 

 is compensated for in testing whole milk by the liberal reading 

 of the fat column, that is, by reading from the bottom of the 

 lower meniscus to the top of the upper one. In skim milk, how- 

 over, since most of the globules are small, a greater proportion 

 of them fail to be driven into the neck of the test bottle ; conse- 

 quently the reading is too low and does not give the true 



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