MANUAL OF GENEEAL AGRICULTUEE. 95 



(c) (1) Warm some milk in a test tube to a tem- 

 perature of the body (98 F.) and add a few drops of 

 rennet. A curd of casein is soon formed. 



2. Kepeat (1), but boil the rennet first. What effect 

 does boiling have on the rennet or enzyme? 



(d) Place 20 c.c. water in an evaporating dish and 

 20 c.c. milk in another evaporating dish. Heat both 

 equally near the fire to boiling. Which boils first ? What 

 does this show about the boiling point of milk compared 

 to that of water? Notice the scum which formed on the 

 boiled milk. Remove it and heat the milk again. Result? 

 What is the nature of this scum? The formation of this 

 scum is not a true coagulation. 



(e) To about 10 c.c. milk add one drop of dilute 

 acetic acid and boil. The casein is coagulated and brings 

 down with it the fat. This is a true coagulation. 



71. ANALYSIS OF MILK. 



Materials : Milk, 2 beakers, cylinder or large beaker, 

 watch crystal, water bath, acetic acid, filter, filter paper, 

 alcohol, stirring rod, ether, crucible, scales. 



(a) 1. Weigh a small beaker, place 50 c.c. of milk 

 in it and weigh again. Subtract and the difference in 

 weight equals the weight of milk taken. Record this 

 weight. 



Pour the 50 c.c. of milk into a large beaker or cylin- 

 der and add 100 c.c. of distilled water. Rinse out the 

 small beaker with 100 c.c. more of distilled water and 

 add to the beaker or cylinder. Be sure the small beaker 

 is well rinsed. Mix well and while stirring gently, add 

 dilute acetic acid (1-10) drop by drop, until the precipi- 

 tate stops forming. Test this by transferring a drop of 

 the liquid to a watch crystal, adding a drop of acetic 

 acid. If no precipitate forms, the solution is ready to set 

 aside over night. This precipitate contains casein and 

 fat. Milk sugar and albumen are in the water solution. 



2. Filter and remove all the casein after it has set 

 over night and save filtrate. Drain carefully, squeeze out 

 water from the filter paper into filtrate. Transfer this, 



