SUGGESTIONS FOR LABORATORY WORK 629 



to the filtrate ammoniacal silver nitrate solution. The precipitate 

 consists of the silver salts of the purin bodies, and will be more 

 abundant after tea, coffee, or cocoa have been taken. 



A STUDY OF MILK 



This is a secretion of the mammary gland and contains Protein, 

 Fat, Carbohydrate (Sugar), and salts in solution. 



The opaque white appearance of milk is due to the presence in 

 it of a protein, caseinogen. This may be precipitated out with 

 acid or by the enzyme rennin. In the latter case the caseinogen 

 combines with some of the calcium of the milk forming casein. 



Fill each of two test tubes 1 / 3 full of milk and add an equal 

 volume of water. 



To one of the tubes add five drops of hydrochloric acid (HC1) ; 

 to the other ten drops rennin solution. Allow both tubes to stand 

 in a water bath at body temperature. 



After twenty minutes filter the contents of both tubes. Make 

 the following tests on each. 



Demonstrate the presence of protein in the precipitate (curd) 

 with the xanthoproteic test. 



Test for fat with osmic acid. 



Apply the biuret test to a few drops of the filtrate (whey). 



Test 2 c.c. of filtrate for sugar with Fehling's test. 



Add to 5 c.c. of the filtrate three drops ammonia (NH 4 OH), 

 and 5 drops sodium oxalate solution. A white precipitate proves 

 the presence of calcium in the filtrate. A careful comparison of 

 acid whey with rennin whey will show that the former contains 

 more calcium. 



