236 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



meniscus at the top and bottom, and the reading should 

 be made from the bottom of the lower meniscus to the 

 top of the upper one. A pair of calipers will be found 

 convenient for measuring the fat column. The tem- 

 perature of the contents of the bottle should be between 

 130 and 140 F. (54 to 60 C.) when the reading is 

 taken. Foam on the top of the fat column is caused by 

 using hard water. Dark colored particles in the fat 

 column may be due to several causes: acid too concen- 

 trated, too much acid, milk too warm when acid was 

 added, allowing acid to mix with milk when placing it 

 in the bottle, allowing the bottle to stand too long before 

 mixing the acid and milk, and interrupting the mixing 

 before the solution was complete. White particles in 

 the fat column may result from acid which is too weak, 

 too little acid, acid or milk being too cold, and insuffi- 

 cient mixing. Immediately after the reading is taken 

 the bottle should be emptied, rinsed out twice with boil- 

 ing water and placed in a rack to drain. Now and then 

 the bottles should be washed in a solution of soap powder 

 or in a dilute solution of lye. 



The Babcock test for fat in cream is made in very 

 much the same manner as for milk, except that a bottle 

 with a longer neck and more extensive graduations is 

 used and the cream is weighed instead of measured. 

 There are two sizes of bottles, one for 9 grammes and 

 the other for 18 grammes of cream. The test bottle is 

 placed on the scales and the cream is introduced into the 

 bottle with a pipette. Sufficient sulphuric acid is added 

 to give the mixture the color of coffee; the quantity 

 required will vary with the per cent, of fat in the cream. 

 The bottle is then whirled in the centrifuge and water 

 added exactly as in testing milk. On being finally re- 



