18 DAIRY CHEMISTRY 



In case there are not enough bottles to fill the 

 machine, arrange the bottles so there will be an 

 even number on each side. If this is not done, 

 the machine is unbalanced, and the bearings will 

 soon become badly worn. The bottles are to be 

 whirled five minutes at the rate of 900 revolutions 

 per minute. Directions for speeding the machine 

 will be found in another paragraph. The start- 

 ing and stopping of the machine should be done 

 gradually. 



After whirling five minutes, the test bottles are to 

 be filled with hot water up to about the eighth mark 

 on the stem. The air bubbles which are sometimes 

 caught in the neck should be allowed to escape. The 

 bottles are then whirled two minutes longer in order 

 to collect all of the fat in the graduated stem. In 

 using the machine always put on the cover so as to 

 prevent any accident. 



None of the apparatus used in this test is patented, 

 and a good homemade centrifugal machine will answer 

 every purpose. The bottles and other glassware can 

 be purchased separately. 



18. Reading the Fat. — ■ When the test is completed, 

 the fat in the stem of the test bottle presents the 

 appearance shown in Fig. 7. Read from the low- 

 est point h to the highest point a. Each large divi- 

 sion, as 1 to 2, represents a whole per cent of fat ; 

 each of the smaller divisions one fifth or two tenths 

 of a per cent. Suppose the top registers seven large 

 divisions, and three small, then a = 7.6. If 6 registers 



