Chemical Analysis of Milk and its Products. 225 



by determing the specific gravity of a, the skim milk, 

 >, the milk serum, and c, the whey. 



282. a. Specific gravity of skim milk. The milk is set 

 in a flat porcelain or glass dish for 12-24 hours in a cold 

 room; the layer of cream formed is then skimmed off, 

 and the sp. gr. of the skim milk determined at 60 F. 

 Skim milk has a sp. gr. of .002 to .0035 (2 to 3.5 lacto- 

 meter degrees) above that of the corresponding whole 

 milk; a smaller difference than this indicates that the 

 milk was skimmed. If both skimming and watering had 

 been practiced, the difference given above might be ob- 

 tained, but the analysis of the milk would in such case 

 easily disclose the adulteration. 



283. b. Specific gravity of the milk serum. To 100 cc. 

 milk 2 cc. of 20 per ct. -acetic acid are added, and the 

 mixture heated in a covered beaker or closed flask for 

 5-10 min. on a water-bath at 55-65 C. After cooling, 

 the milk serum is filtered off and its sp. gr. determined 

 at 60 F. In case of pure milks, the sp. gr. of the milk 

 serum (at 60) will come above 1.0270. Serum from 

 normal milks contain 6.3 to 7.5 per ct. solids and .22 

 to .28 per ct. fat; by the addition of 10 per ct. of water, 

 the solids in the serum are lowered .3 to .5 per ct., and 

 the sp. gr., .0005. 1 



c. Specific gravity of whey. 500 cc. of milk are warmed 

 in water of 40-50 C. until its temperature is 35 C.; 

 one-half cc. of rennet extract (12-15 drops) is added, 

 and the milk stirred thoroughly. After allowing the 

 curd to solidify for 10 minutes, it is cut and the whey 

 filtered off through several layers of cheese cloth. The 



iKonig, Menschl. Nahrungsmittel II, p. 276. 

 15 



