78 QUESTIONS AND ANSWERS 



What points should receive special attention in 

 making the Hart casein test? 



1. The temperature of the milk and acid solu- 

 tion must be right. 



2. The mixture must be shaken properly and for 

 the right length of time. 



3. The speed of the centrifuge must be sufficient, 

 yet not too great. 



4. Allow ten minutes to elapse after complet- 

 ing the whirling before reading the test. 



What coloring matters are sometimes added to 

 milk? 



1. Annatto. 



2. Coal-tar colors. 



3. Caramel. 



How does artificially colored milk differ in appear- 

 ance from uncolored milk? 

 In uncolored milk the natural yellow is contained 

 largely in the cream. In colored milk the color 

 remains after the cream has risen or been removed. 

 The skim milk does not show the familiar bluish 

 tint when coloring matter has been added. 



What is the nature of annatto coloring matter? 



Annatto is a reddish-yellow coloring matter ex- 

 tracted by weak alkaline solutions from the pulp 

 inclosing the seeds of a shrub that grows in South 

 America and the West Indies. The alkaline solu- 

 tion is used for coloring purposes. 



Give a simple test for annatto coloring in milk. 

 In a tig^htly corked vial or test tube shake 



