THE ANALYSIS OF MILK 665 



To make the indicator : — 



Dissolve o'5 grm. of starch by boiling in water. 

 Dissolve 10 grm. of KI in water. 

 Mix and make up to 100 c.c. 



Example : j'l c.c. of diluted milk were required 



But 7*2 c.c. of diluted milk = g"o678 grm. lactose 

 Since 10 c.c. Fehling's solution = o"o678 grm. laciose 

 Hence 100 c.c. of diluted milk = o"678 x 100 grm. lactose 



7-2 



But this is in 20 cc. sample of milk 



.•. In 100 c.c. sample of milk = 0*0678 x 100 x 100 



= 47 per cent, lactose 



7-2 X 20 



(6) To Estimate the Specific Gravity. 



This can be estimated by Westphal's balance, the Sprengel tube 

 lactometer, or the specific gravity bottle. The lactometer is best for 

 tropical use. 



It is usually between 1028 and 1034. 



(7) To Estimate Amount of Added Water and Deficiency of Fat. 



These are obtained from two simple formulse. 

 (A) 8-5 - S.N.F. X 100 



per cent, added water 

 8-5 



S.N.F. solids not fat found in sample, e.g., 27 



E.X8-5 - 7-5 



X 100 = 107 per cent, of added water 



8-5 



{B)3-F 



X 100 = per cent, deficient in fat. F. = fat in sample, e.g., 27 



J^X o 2"7 



■ X 100 = 10 per cent, deficient m fat 



3 



(8) Common Preservatives are: — 



(i) Boric Acid. 



Acidify 3 c.c. of milk in a test-tube with distilled HCl. 



Mix well and place a drop on a turmeric paper. 



Dry same on watch glass in oven. 



A red spot indicates that boric acid is present. 



This turns green instead of black on adding caustic potash. 



(2) Formaldehyde. 



In a test-tube place 10 c.c. of milk. 



Add 10 c.c. of concentrated HCl and one drop of ferric 



chloride. 

 Stir well, heat to boiling. 

 A violet colour indicates formaldehyde. 



