216 MILK 



Both Skimmed and Watered 

 The amount of fat removed from -the milk = 



^ 100 



In these formulas the letters stand for: 



r = plasma solids. 



f = fat content. 



M = the amount of whole milk contained in 100 parts watered 

 milk. 



fi = the per cent, of the normal (barn) milk. 



ii = the per cent, of fat in the suspected milk. 



ri = the per cent, plasma soKds in the normal (barn) milk. 



r2 = the per cent, plasma soUds in the suspected milk. 



The index of oxidation of milk has been recommended by 

 Commanducci as a check upon watering milk. A one-tenth nor- 

 mal potassium permanganate solution in acid is placed in a biuet 

 and discharged into 1 c.c. of milk. The nmnber of cubic centi- 

 meters required to complete the reaction is the index of oxidation, 

 which is uniform for milk from the same species. The index 

 decreases when the milk has been watered, skimmed, or both 

 watered and skimmed. The normal figures as given by the 

 author are these: Cow, 50-52; goat, 44-46; sheep, 43-48; ass, 

 55-58; human, 53-60. 



The lactoscope (Fig. 82) is an instrument designed to esti- 

 mate the amount of fat in milk, although the values obtained are 

 only approximate. A white glass cylinder with black Hues is 

 fitted by means of a stopper into a larger glass of cyhndric shape, 

 constricted below and having an aperture at the top. Four c.c. 

 of the milk are measured accurately and placed in the large 

 glass cylinder. Enough water is added to permit the black lines 

 of the small cylinder to appear clearly. The line on a level with 

 the surface of the liquid indicates the amount of fat. This 

 instrument gives only the amount of fat without taking into 

 account the amount of other solids. Therefore a rich milk might 

 be diluted and still show a reasonable amount of fat, but in con- 

 nection with the specific gravity watered or skimmed milk can 

 usually be detected by the lactoscope. 



Since the fat is the most variable constituent of milk, the milk 

 serum containing all the other solids has been used for determining 

 whether water has been added to the milk. The specific gravity 

 of the serum is fairly constant and, when below normal, indicates 

 watering. Milk serum can be prepared by the use of calcium 

 chlorid or by coagulation with acetic acid. 



