MILK. 225 



1 6. Detection of Lactose. Concentrate the nitrate from the 

 calcium phosphate until it is of a syrup-like consistency. Allow it 

 to stand over night and observe the formation of crystals of lac- 

 tose. Make the following experiments : 



(a) Microscopical Examination. Examine the crystals and com- 

 pare them with those in Fig. 75, page 220. 



(&) Fehling's Test. Try Fehling's test upon the mother liquor. 



(c) Phenylhydrazine Test. Apply the phenylhydrazine test to 

 some of the mother liquor according to the directions given on 

 page 24. 



17. Milk Fat. (a) Evaporate the ether filtrate from the case- 

 inogen (Experiment 13) and observe the fatty residue. The milk 

 fat was carried down with the precipitate of caseinogen and was 

 removed when the latter was treated with ether. If centrifugated 

 milk was used in the preparation of the caseinogen the amount 

 of fat in the ether nitrate may be very small. To secure a larger 

 yield of fat proceed according to directions given under (b) below. 



(b) To 25 c.c. of whole milk in an evaporating dish add a 

 little sand or filter paper and evaporate the fluid to dryness on a 

 water-bath. Grind or break up the residue after cooling and ex- 

 tract with ether in a flask. Filter and remove the ether from 

 the filtrate by evaporation. How can you identify fats in the 

 ethereal residue? 



1 8. Saponification of Butter. Dissolve a small amount of but- 

 ter in alcohol made strongly alkaline with potassium hydroxide. 

 Place the alcoholic-potash solution in a casserole, add about 100 

 c.c. of water and boil for 10-15 minutes or until the odor of alco- 

 hol cannot be detected. Place the casserole in a hood and neutralize 

 the solution with sulphuric acid. Note the odor of volatile fatty 

 acids, particularly butyric acid. 



19. Detection of Preservatives. (a) Formaldehyde. 



I. Gallic Acid Test. Acidify 30 c.c. of milk with 2 c.c. of nor- 

 mal sulphuric acid and distil. Add 0.2-0.3 c.c. of a saturated 

 alcoholic solution of gallic acid to the first 5 c.c. of the distillate, 

 then incline the test-tube and slowly introduce 3-5 c.c. of concen- 

 trated sulphuric acid, allowing it to run slowly down the side 

 of the tube. A green ring, which finally changes to blue, is formed 

 at the juncture of the fluids. This is claimed, by Sherman, to be 

 twice as delicate as either the sulphuric acid or the hydrochloric 

 acid test for formaldehyde. 



II. Leach's Hydrochloric Acid Test. Mix 10 c.c. of milk and 

 16 



