7. Milk sugar, or lactose, ffltms more than one-third of the solids of milk and more than 

 one-half of the solids of separator skim milk. To prepare miik sugar in the laboratory, coagu- 

 late about 50 cc. of skim milk with a few drops of acetic acid. After coagulating the milk, 

 strain out the curd, (largely casein) and heat the remaining liquid to the boiling point. (Save 

 a little of the curd for experiment 8.) Boiling will precipitate the albumen, (a) Albumen 

 and casein together form what? See foot note on page 159. (b) After the albumen has set- 

 tled, pour off the clear liquid, or filter it and then boil to dryness in an evaporating dish. 

 Describe the appearance of the material left in the dish, (c) Compare its taste with that of 

 cane sugar — ordina/y sugar, (d) What do you remove when you skim milk? (e) What do 

 you remove when you make cheese out of skim milk? What is left in the whey? 



8. (a) Test a little curd of milk for protein by use of nitric acid and ammonia, as in 

 previous work. Record the results of the test, (b) What other form of protein is present in 

 milk? 



Part C. Sterilization, Pasteurization, and the Making of "Artificial Butter Milk." 



9. (Classroom experiment.) Boil about 100 cubic centimeters of milk in a beaker for 

 twenty minutes. The boiling temperature is about 212° F. or 100° C. (a) Describe the appearance 

 and taste of the milk after boiling, (b) Let it stand for a day in a cool place and observe 

 whether or not the cream rises as it does on milk not boiled, (c) Does sterilized milk sour 

 as quickly as milk not sterilized? Explain. 



10. Fill a 50 cc. beaker about Yi full of milk. Set it in a 200 cc. beaker or a tin cup nearly 

 full of water. Heat the water until the temperature of the milk in the small beaker becomes 

 about 155° F. or about 68° C. (a) Observe the appearance and taste of the milk after being 

 heated to this temperature, (b) Let it stand for a day in a cool place and observe whether or 

 not cream rises on this milk as it does on milk not heated, (c) This process of treating milk 

 is called pasteurization. How did the name pasteurization come to be applied to this process 

 of treating milk? For reference, consult encyclopaedia, (d) In what respect is pasteurized 

 milk not as good as sterilized milk? (e) Wherein does it have an advantage over sterilized 

 milk? 



11. Make a little "artificial buttermilk" by use of Lactone tablets (cultivated bacteria). 

 Follow as far as possible the directions given in the printed matter which accompanies the box 

 of tablets, (a) What do the directions say concerning the temperature at which these bac- 

 teria do their best work? (b) What is said concerning the length of time during which these 

 bacteria may be kept? (c) What do you infer concerning the length of life of the bacteria 

 present in these tablets? 



160 



