Nine grams are usually used instead of 18. The correction is 

 made in the reading. 



Conclusion: The whole milk tested %. The 



skim milk tested.. %. The cream tested %. 



EXERCISE No. 33 

 PHYSICAL PROPERTIES OF MILK 



Object: To become familiar with the physical properties 

 of milk. 



Material: Samples of whole milk, cream, skim milk, a 

 compound microscope, beakers, a lactometer, and olive oil. 



Method: 1. Examine a sample each of cream, whole 

 milk, and skim milk under a compound microscope. 



~ (a) Make a detailed drawing of a section of the field. 

 (1) cream; (2) whole milk; (3) skim milk. 



(b) What is the nature of the distribution of the globular 

 bodies in each field? Can you infer what has caused the 

 changes? 



2. Add a few drops of olive oil to a test tube half full of 

 water. After vigorously shaking the test tube, hold it in 

 the light and observe the change that takes place. 



(a) What is the proof that oil is lighter than water? 

 Why does cream rise to the surface of the milk when left 

 in a quiet place? 



3. By the use of a lactometer determine the comparative 

 weights of water, skim milk and whole milk. Does the heavy 

 or light liquid exert the greater upward pressure (buoyant 

 force) on the lactometer when submerged in it? 



63 



