MILK 



443 



tube add 0.4 c.c. of a 4 per cent, alcoholic solution of benzidine and 

 0.2 c.c. acetic acid. Blue coloration of the mixture = hydrogen 

 peroxide. 



5. Salicylic Acid. 



Precipitate the caseinogen by the addition of acetic acid and 

 filter. To the filtrate add a few drops of i per cent, aqueous solu- 

 tion of ferric chloride. Purple coloration = salicylic acid. 



6. Sodium Carbonate or Bicarbonate. 



To 10 c.c. of the milk in a test tube add 10 c.c. of alcohol and 

 0.3 c.c. of a i per cent, alcoholic solution of rosolic acid. Brownish 

 color = pure milk; rose color = preserved milk. 



Quantitative. 



Collection of Sample. 



The apparatus used for the collection of a retail 

 mixed milk sample consists of a cylindrical copper case, 

 1 6 cm. high and 9 cm. in diameter, provided, with a 





FIG. 211. Milk-collecting bottle and dipper in case. 



"pull-off" lid, containing a milk dipper, also made of 

 copper; and inside this, again, a wide-mouthed, stop- 

 pered glass bottle of about 250 c.c. capacity (about 14 

 cm. high by 7 cm. diameter), having a tablet for notes, 

 sand-blasted on the side. The copper cylinder and its 



