MILK. 223 



0.1-0.3 c.c. of M/io hydrogen peroxide and i c.c. of a one per cent 

 solution of "trikresol." A slight, though unmistakable yellow 

 color will be observed to develop throughout the solution. 



Repeat the test using milk which has been boiled or heated to 

 80 C. for 10-20 minutes, and cooled, and note that no yellow 

 color is produced. 



The color reaction in the case of the raw milk probably results 

 from the oxidation of the cresols by the hydrogen peroxide. The 

 first product of this oxidation 1 then oxidizes the leuco compound, 

 when such is present, and causes the color observed. 



11. Saturation with Magnesium Sulphate. Place about 5 c.c. 

 of milk in a test-tube and saturate with solid magnesium sulphate. 

 What is this precipitate? 



12. Influence of Gastric Rennin on Milk. Prepare a series of 

 five tubes as follows: 



(a) 5 c.c. of fresh milk -f- 0.2 per cent HC1 (add drop by 

 drop until a precipitate forms). 



(b) 5 c.c. of fresh milk -f- 5 drops of rennin solution. 



(c) 5 c.c. of fresh milk + 10 drops of 0.5 per cent Na 2 CO 3 . 



(d) 5 c.c. of fresh milk -f- 10 drops of ammonium oxalate. 



(e) 5 c.c. of fresh milk + 5 drops of 0.2 per cent HC1. 

 Now to each of the tubes (c), (d) and (e) add 5 drops of 



rennin solution. Place the whole series of five tubes at 40 C. 

 and after 10-15 minutes note what is occurring in the different 

 tubes. Give a reason for each particular result. 



13. Preparation of Caseinogen. Fill a large beaker one-third 

 full of skimmed (or centrifugated) milk and dilute it with an equal 

 volume of water. Add dilute hydrochloric acid until a flocculent 

 precipitate forms. Stir after each acidification and do not add an 

 excess of the acid as the precipitate would dissolve. Allow the 

 precipitate to settle, decant the supernatant fluid and reserve it for 

 use in later (14-16) experiments. Filter off the precipitate of 

 caseinogen and remove the excess of moisture by pressing it be- 

 tween filter papers. Transfer the caseinogen to a small beaker, add 

 enough 95 per cent alcohol to cover it and stir for a few moments. 

 Filter, and press the precipitate between filter papers to remove 

 the alcohol. Transfer the caseinogen again to a small dry beaker, 

 cover the precipitate with ether and heat on a water-bath for ten 

 minutes, stirring continuously. Filter (reserve the filtrate), and 

 press the precipitate as dry as possible between filter papers. Open 



1 Probably some organic peroxide or quin'oid compound. 



