Laboratory Exercises 365 
25. Roucu ANatysis or MILK 
Object. To become familiar with the constituents of milk. 
Materials. Milk, two-quart fruit jar, cheese cloth, beakers, ren- 
net, funnels, filters, thermometer, platinum or porcelain evaporat- 
ing dishes, test tubes. 
Directions. Place about one pint of milk in a two quart fruit 
jar. Heat to about 70F. Shake vigorously until lumps of a 
yellowish substance collect. This substance is butter. Some 
fat will remain in the milk and cannot be collected. Remove the 
fat by straining through cheese cloth. The milk which runs 
through is called skimmed milk, or milk serum. 
-Empty the skimmed milk into a convenient dish, such as a beaker. 
Heat to about 90 F. and add one cubic centimeter of rennet, 
stir thoroughly for about 15 to 20 seconds. Let stand for about 
10 minutes. Strain through three thicknesses of cheese cloth. 
The white material which remains on the cloth is casein or curd. 
Filter some of the material which goes through the cheese cloth 
through filter paper, so that it is clear. Boil for about one minute 
about 25 cubic centimeters of the filtrate in a test tube or beaker. 
The white flocculent precipitate is albumen. Filter the solution 
through a filter paper. The albumen will collect on the filter. 
Collect the filtrate and evaporate it to dryness in a platinum or 
porcelain dish. The substance which remains is principally milk 
sugar. 
26. QuaLiTaATIVE DETERMINATION or MILK AsH 
Object. To determine the ash of milk qualitatively. 
Materials. Milk, graduated pipette, nitric acid concentrated, 
platinum or porcelain evaporating dishes, water bath. 
Directions. Place in a platinum or porcelain evaporating dish 
18 cubic centimeters of milk, add 5 cubic centimeters of concen- 
trated nitric acid. Heat to dryness in a water bath. Burn to 
a gray ash over a low flame. Do not burn too rapidly. 
