112 Testing Milk and Its Products. 



122. Latitude of variation. In order to determine 

 whether or not a sample of milk is skimmed or watered, 

 or both skimmed and watered, the per cents, of fat and 

 of solids not fat in the sample must be ascertained, and 

 if a control-sample can be secured, these determina- 

 tions for both samples compared. The proper latitude 

 to be allowed for the natural variation in the composi- 

 tion of milk differs according to the origin of the milk; 

 in case of milk from single cows, the variations in fat 

 content from day to day may exceed one per cent., al- 

 though under ordinary conditions the per cent, of fat 

 in most cow's milk will not vary that much. The con- 

 tent of solids not fat is more constant, and rarely va- 

 ries one-half of one per cent, from day to day with 

 single cows. Cows in heat or sick cows may give milk dif- 

 fering considerably in composition from normal milk.' 



123. Mixed herd milk is of comparatively uniform 

 composition on consecutive days, and as most milk of- 

 fered for sale or delivered to factories is of this kind, 

 the task of the milk inspector is made considerably 

 easier and more certain on this account. Daily varia- 

 tions in herd milk beyond one per cent, of fat and one- 

 half per cent, of solids not fat, are suspicious and may 

 be taken as fairly conclusive evidence of adulteration. 

 This is especially true in case the control-sample shows a 

 comparatively low content of fat or solids not fat (159). 



124. Legal standards. Where a control-sample can- 

 not be taken, the legal standards of the various states 

 for fat or solids in milk are used as a basis for calculat- 



' Blythe, Foods, their Composition and Analysis, London, 1903, p. 

 250 et seq. 



