PRODUCTION, COMPOSITION AND CHARACTERISTICS 17 



milk and the percentage can be easily determined. 

 Centrifugal force had already been used in the Fjord 

 Cream Test, but it remained for Dr. 

 Babcock to work out the splendid 

 practical and reliable test which bears 

 his name and in which he has given 

 to the world an invention of incal- 

 culable value. 



Sampling. — Whether it is new milk ^ ^ , _, 

 , . .„ , „, A two-bottle machine 



or skim milk or buttermilk or cream 



that is to be tested the first thing to observe is to take 

 a truly representative sample. The liquid must be thor- 

 oughly mixed by pouring it several times from one ves- 

 sel to another, or stirring vigorously. 



the milk in the test bottle. The acid is a strong poison and must be 

 handled with care. Pour it slowly down along the wall of the bottle 

 which is held at an angle and turned slowly during the operation. 



Now give the bottle a rotary motion to thoroughly mix the milk 

 and the acid, shaking vigorously towards the end of the operation so 

 as to be sure not to leave any of the acid which is heavier than the milk 

 at the bottom of the bottle. 



Whirling. — The bottles are then placed in the centrifugal machine 

 and whirled for five minutes at the proper speed — from 600 to 1 200 

 revolutions per minute — according to the diameter of the machine 

 and as stated in the directions which come with the tester. The mix- 

 ture of milk and acid is hot enough if the whirling is done at once, but 

 if it is allowed to cool the bottles should be placed in hot water of 150 

 to 170° for about 15 minutes; whirhng at full speed for 4 minutes brings 

 all the fat to the top. 



Hot water is now added until the bottle is filled almost to the scale 

 on the neck and the bottles are again placed in the machine and whirled 

 at full speed for one minute. Hot water is then again added until 

 the lower end of the fat column is within the scale, preferably at the 

 1% or 2% mark on the neck of the bottle. Whirl once more for 

 one or two minutes and then read off the percentage of fat on the scale. 

 Each division represents 0.2% fat. The fat column is measured from 

 the lower line between the fat and the water to the point where the top 

 of the fat column touches the wall of the neck. A pair of dividers are 

 handy for measuring the fat column and reading off the percentage of 



