MILK. 81 



(6) Take the specific gravities and explain the variations 

 in the results. 



(c) Test the reaction with litmus paper. 



(d) Saturate 10 c.c. of milk with MgSO 4 . What is the 

 precipitate? 



(e) Shake 5 c.c. of milk with ether. What takes place? 

 Now add a few drops of NaOH. Explain this change. 



(/) Heat some milk in an evaporating-dish. Notice the 

 scum. 



(</) Heat 5 c.c. of milk and 5 c.c. of NaOH to boiling. 

 The yellowish-brown coloration is caused by the action of 

 the alkali on the lactose. 



(/i) Try the guaiac reaction described under blood, using 

 milk instead. Explain the result. 



QUALITATIVE SEPARATION OF THE CONSTITUENTS 

 OF MILK. 



Dilute 200 c.c. of milk with 800 c.c. of water and add weak 

 acetic acid, drop by drop, until a white flocky precipitate 

 separates out, leaving a fairly clear solution. Allow the pre- 

 cipitate to settle; then filter (Filtrate A) it off and let it 

 drain as dry as possible. Remove the white precipitated 

 caseinogen from the paper and place it in a flask with 200 c.c. 

 of a mixture one-half ether and one-half alcohol. Allow the 

 precipitate to stand in contact with the ether for an hour, 

 shaking from time to time. Then filter off the ether mix- 

 ture and let it evaporate spontaneously. The residue con- 

 sists of most of the fat of the milk, mechanically precipitated 

 adherent to the caseinogen. Keep both the caseinogen and 

 the fatty residue. 



Place the filtrate A in an evaporating-dish and heat over 

 a free flame ; the solution being acid, any coagulable protein 



