226 Testing Milk and Its Products. 



a porcelain casserole ; a few drops of an alcoholic phe- 

 nolphtalein solution are added, and soda solution is 

 dropped in slowly from a burette until the color of the 

 milk remains uniformly pinkish on agitation. 1 cc, of 

 Y^ alkali corresponds to .009 gram lactic acid, or to 

 .045 per cent, when 20 cc. of milk are taken (see p. 121). 



B. CREAM, SKIM MILK, BUTTER MILK, WHEY, CON- 

 DENSED MILK. 



262. The analysis of these products is conducted in 

 the same manner as in case of whole milk, and the same 

 constituents are determined, when a complete analysis 

 is wanted. Skim milk, butter milk, and whey con- 

 tain relatively small quantities of solids, and espe- 

 cially of fat, and it is, therefore, well to weigh out a 

 larger quantity than in case of whole milk; if possible, 

 toward 10 grams. The acidity of sour milk and butter 

 milk must be neutralized with sodium carbonate pre- 

 vious to the drying and extraction, as lactic acid is solu- 

 ble in ether and would thus tend to increase the ether- 

 extract (fat), if not combined with an alkali previous 

 to the extraction. 



263. Specific gravity of butter milk. The specific gravity 

 of butter milk (as well as of sour or loppered milk) is deter- 

 mined by Weibull 's method ; a known volume of the milk is 

 mixed with a certain amount (say 10 per cent.) of ammonia of 

 a definite specific gravity, and the specific gravity of the liquid 

 determined after thorough mixing and subsequent standing for 

 an hour. If A designate the volume of butter milk taken, B that 

 of ammonia, and C that of the mixture; and if furthermore S 

 designate the specific gravity of the butter milk, s^ that of the 

 ammonia, and s 2 that of the mixture, we have 



Cs 2 Bs, 



