28 ANALYTICAL PROCESSES. 



the zero point, with a mixture of sulfuric acid 

 and water prepared at the time. It is then placed in 

 the centrifugal machine, which is so arranged that when 

 at rest the bottles are in a vertical position. If only 

 one test is to be made, the equilibrium of the machine is 

 maintained by means of a test-bottle, or bottles, filled 

 with a mixture of equal parts of sulfuric acid and wa- 

 ter. After rotation for from one to two minutes, the fat 

 will collect in the neck of the bottle and the percent- 

 age may be read off. It is convenient to use a pair 

 of dividers in making the reading. The legs of these are 

 placed at the upper and lower limits respectively of the 

 fat, allowance being made for the meniscus; one leg is 

 then placed at the zero point and the reading made with 

 the other. The results do not differ from those obtain- 

 ed by the Adams' process by more than one-tenth per 

 cent., and are generally even closer. 



Cream is to be diluted to exactly ten times its volume, 

 the specific gravity taken, and the liquid treated as a 

 milk. Since in the graduation of the test-bottles a 

 specific gravity of 1030 is assumed, the reading must 

 be increased in proportion. 



A more accurate result may be obtained by weighing 

 in the test-bottle about 2 c. c. of the cream and di- 

 luting to about 15 c. c. The reading obtained is to be 

 multiplied by 15.45 an d divided by the weight in grams 

 of cream taken. 



Calculation Method Several investigators have 



proposed formulae by which when any two of the data, 



