214 Testing Milk and Its Products. 



contain only small quantities of solids, and especially of 

 fat, and it is, therefore, well to weigh out a larger quan- 

 tity 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 previous to the dry- 

 ing and extraction, as lactic acid is soluble in ether and 

 would thus tend to increase the ether-extract (fat), if not 

 combined with an alkali previous to the extraction. 



260. Specific gravity of butter milk. The specific grav- 

 ity of butter milk (as well as of sour or loppered milk) 

 is determined 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 desig- 

 nate the volume of butter milk taken, B that of ammo- 

 nia, and C that of the mixture; and if furthermore s de- 

 signate the specific gravity of the butter milk^ that of 

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



_Cs !i -B8 1 

 A 



Klein 1 has modified this method by weighing the 

 liquids, thus securing greater accuracy; 22 to 24 per cent. - 

 ammonia is used, one- tenth as much being taken as the 

 amount of milk weighed out. The results come uniformly 

 .0005 too high, and this correction should always be made. 

 The following formula will give the specific gravity of the 

 milk, which in case of careful work will be accurate to 

 one-half lactometer degree; if the letters given above 

 designate weights (instead of volume as before) and 



specific gravities of the liquids, respectively, we have 



A 



s=- 



C B 



i Milchzeitung, 1896, p. 656. 



