28 



10. Determining fat in cheese by Babcock method. — The method is 

 less satisfactory, owing to difficulty of sampling cheese. It is neces- 

 sary to weigh the cheese, using about 5 grams. Then add 15 cubic 

 centimeters of hot water and shake to an emulsion. Then add acid 

 and proceed as before. The per cent of fat read on bottle must be 

 multiplied by 18 and divided by the number of grams of cheese used 

 (reference No. 3, p. 109, or No. 12, p. 77). 



EXPERIMENT AND PRACTICE WORK, FOURTH LECTURE. 



Time required. — One's first test can probably be made in twenty 

 minutes, but the details should be often repeated so that one can 

 acquire rapidity and accuracy. It would be well to devote two hours 

 the first day to the test and then use the test afterwards every day as 

 opportunity offers. 



Apparatus and materials required. — See paragraph 5, preceding. 

 In addition, 1 " N-H" milk-bottle tester. 



1. Use of pipette. — Practice drawing milk into pipette and bringing 

 to mark until it can be done quickly and accurately (reference No. 

 12, p. 27). 



2. Running milk into test bottle from pipette. — After filling pipette 

 properly run milk into test bottle, so that milk will all be delivered 

 without running over (reference No. 3, p. 104, or No. 12, p. 128). 



3. Measuring acid and pouring into test bottle. — (Reference No. 3, 

 p. 104, or No. 12, p. 28.) Practice pouring acid into bottle so that it 

 will run down side of bottle and form a layer under the milk without 

 mixing with it. In handling sulphuric acid be careful not to get it on 

 the skin or clothing. 



4. Mixing milk and acid. — (Reference No. 3, p. 105, or No. 12, p. 30.) 

 Practice giving the bottles the peculiar kind of rotary motion that 

 mixes the milk and acid without throwing any out of the bottle. 



5. Whirling test bottles and adding water. — (Reference No. 3, p. 105, 

 or No. 12, p. 31.) Observe carefully precautions as to rapidity of rev- 

 olution. Determine number of revolutions made per minute (refer- 

 ence No. 12, p. 50) in relation to number of turns of handle. 



6. Measuring fat. — Practice reading fat in graduated neck (refer- 

 ence No. 3, p. 106, or No. 12, p. 32). 



7. Measuring accuracy of test bottles. — Use brass plunger milk-bottle 

 tester according to directions given with the apparatus. 



8. Testing other substances than milk for fat. — After acquiring 

 facility in making tests with milk test skim milk, whey, butter, and 

 cheese (reference No. 3, pp. 108, 109, or No. 12, pp. 74-77). 



