TESTING 243 



when they are normal. On the other hand, when the 

 temperatures are low, a slightly larger amount of acid 

 may be used. 



4. Shake the test-bottles until the milk and acid are 

 thoroughly mixed. It is difficult to secure a clear test 

 if the agitation of the acid and milk has not been thorough. 

 A rotary motion should be used so as not to fill the neck 

 of the bottle with coagulum. 



5. Place the test-bottles in the centrifuge and revolve it 

 at the required speed as indicated by the directions on 

 the machine. 



6. After centrifuging for five minutes, stop the ma- 

 chine and fill each to the shoulder with warm or hot 

 water as the conditions may require. The tempera- 

 ture of the water will depend on that of the machine and 

 of the room. If the centrifuge is very hot, due to poor 

 steam exhaust, the water should probably not be above 

 110 to 120 F. In the hot summer season, when the 

 milk and the acid are warm, the temperature of this 

 water should be about 110 F. and not boiling. 



7. Revolve the centrifuge at the required speed. 



8. At the end of two minutes of centrifuging at full 

 speed, stop and fill the test-bottles with hot water. The 

 fat should be raised toward the top of the graduation in 

 the neck of the bottle. Care must be taken to prevent 

 the overflowing of the test-bottles. 



9. Revolve the centrifuge for one minute at the required 

 speed. 



10. Read the tests, which should now have clear dis- 

 tinct lines. The fat should be a straw-yellow color and 

 the liquid under the fat should be as clear as crystal. 

 The tests should be read as they are taken from the centri- 

 fuge and before they are cooled. The reading should 



