32 MILK ANALYSIS 



Adulterations. — The addition of water to milk is usual!)' 

 detected by the diminution in the amount of solids. The ad- 

 dition of water decreases the specific gravity, while abstraction 

 of fat increases it. 



Several observers have found that the whey (milk-serum) 

 obtained by a routine method is of constant composition and 

 that by its specific gravity or refractive index, watering may be 

 detected. Woodman recommends the following method for 

 obtaining a standard whey: loo c.c. of the sample are mixed 

 with 2 c.c. of dilute acetic acid (sp. gr. 1035, containing 25 per 

 cent, acetic acid), the vessel covered with a watch-glass and heated 

 in the water-bath for 20 minutes, at 70.° It is then placed 

 in ice-water for 10 minutes, and the solution filtered. The 

 specific gravity may be taken under the usual precautions, or, 

 as suggested by Leach, the refractive index may be observed. 

 The routine of precipitation must be closely followed, as the 

 amount of proteids precipitated differs with the method. The 

 total solids and polarimetric reading of the whey might be taken 

 as additional data. The latter figure will be somewhat less 

 than that due to the milk-sugar, as the proteids in solution are 

 levorotatory. 



The following are some of the limits recorded, but analysts 

 should make determinations on samples of known composition. 



For the Zeiss immersion refractometer, an instrument of 

 special, construction. Leach & Lythgoe consider 39 as the 

 lowest permissible reading. This corresponds to 1.3424 on the 

 Abb^ refractometer. 



From unwatered whole milk. Leach obtained a serum of sp. 

 gr. 1.0287; from unwatered centrifugal skimmed milk, a serum 

 of 1.0296, at 15°- 



Vieth has pointed out that in normal milks the ratio sugar: 

 proteids : ash =13:9:2 exists, and a determination of these 

 ratios may aid in the attempt to distinguish genuine but ab- 

 normal milks from watered milks. In the case of a watered 



