MILK TESTING. 33 
67. Test for Casein in Milk. 
If it is desired to determine the amounts of casein in differ- 
ent samples of milk, the following test invented by Prof. Hart 
of the Wisconsin Station in 1907* may be used to advantage in 
factory work as well as in chemical laboratories: Two e. ¢. of 
chloroform, 20 ¢. ec. of a .25 per cent acetic-acid solution, and 5 
e. c. of milk (both these latter of a temperature of about 70° F.) 
are measured into small tubes of special construction holding 
about 35 ¢. ¢., the lower end of which is narrow and graduated 
to 1 ¢. ¢. The mixture is shaken for 15 to 20 seconds and the 
tubes then whirled 714 to 8 minutes in a centrifuge of 15 inches 
diameter, making 2000 revolutions per minute. The use of a 
metronome is recommended to facilitate the control of the speed. 
After whirling, the tubes are taken out of the centrifuge and 
allowed to stand in an upright position for 10 minutes. The per- 
centage of casein may then be read off directly from the scale 
on the lower end of the tubes; each division of the scale repre- 
sents .2 per cent of casein when 5 c. c. of milk are measured out. 
QUESTIONS ON CHAPTER III. 
1. When and by whom was the Babcock milk test invented ? 
2. Describe the test bottle. 3. What is the volume included in 
the scale of the milk bottle and how is it divided? 4. What is 
the volume of the pipette and what weight of milk will it hold? 
5. What is the volume of the acid measure? 6. What is the 
diameter of the centrifuge? 7. How is a test made? 8. What 
kind and how strong is the acid used? 9. At what speed should 
the centrifuge be run? 10. Describe how the fat should be read. 
11. How can cheese be tested with the Babcock test? 12. De- 
scribe the Quevenne lactometer. 13. Describe the Board of 
Health lactometer and state its relation to the Quevenne. 14. 
How much does each per cent of fat lower the lactometer read- 
ing? 15. Give method and rule for detecting watered milk. 
16. What is a composite sample? 17. Describe the Scovell 
sampling tube. 18. How are composite samples taken and pre- 
served? 19. Describe Hart’s test for casein in milk. 
*Report 24, p. 117. 
