17 



2. Action of alkalis on casein compounds. — Prepare some casein 

 acetate, as described in preceding experiment. Dissolve some sal soda 

 in water and add some of this solution to the white, solid casein ace- 

 tate. Agitate. The casein acetate is dissolved, the casein combining 

 with sodium, forming sodium caseate, which is easily soluble in water. 



3. Preparation of mill- sugar. — Take a pint or more of whey and 

 evaporate it to about one-eighth of its original bulk. Let it stand 

 until the next day. Impure milk sugar separates in solid form. How 

 does it compare in sweetness with cane sugar? Place some of it on a 

 stove or hot iron. What is the odor produced? 



4. If a good microscope is available, place one drop of diluted milk 

 (1 part of milk diluted with 10 parts of water)' on a glass sHdc, put a 

 cover glass over it and examine with different magnifying powers. 

 Study the fat globules, noticing their variation in size. Take a small 

 piece of cheese and mix it very completely with several times its bulk 

 of warm water. Then take one drop of this water extract and exam- 

 ine it under the microscope for fat globules. Examine a drop of undi- 

 luted whey and of skim milk. 



5. Melt about half a pound of butter and ])oui it into a glass tum- 

 bler. Let it stand twenty-four hours at 60° to 80° F. Notice the 

 separation of fat from the brine. Notice the granular structure of 

 the fat and the fact that some of it ap])ears to be more or less licjuid 

 through the mass. This shows that butter fat contains different fat 

 compounds. 



SECOND LECTURE. 



THE COMPOSITION OF COW's MILK IN RELATION TO THE MANUFACTURE 



OF CHEESE. 



Only withm fifteen years has there been a thorough study of the 

 relations of milk to cheese. The whole attention was formerly given 

 to methods of cheese making, and none to such fundamental questions 

 as the relation of fat and casein in milk to yield and quality of cheese, 

 the character and extent of losses of milk constituents in cheese mak- 

 ing, their causes and remedies, etc. 



1. Yield of cheese variable witli different milks. — It is a fact of com- 

 mon experience at cheese factories that the amount of cheese made 

 from 100 pounds of milk varies. Provided the conditions of manufac- 

 ture are the same, such differences are due to differences in the com- 

 position of milk. - 



2. Yield of cheese dependent upon certain constituents of milk. — It has 

 been shown that the yield of cheese depends most largely upon the 

 two milk constituents, /ai and casein (reference No. 3, p. 89). 



3. Milk solids divided into two classes. — We may divide the solids of 

 milk into two general classes: (1) Cheese-producing and (2) whey-pro- 

 ducing. The former includes fat and.casein ; the latter albumin, suga r , 



25300— No. 166—06 3 



