TESTING MILK FOR ADULTERATIONS 143 



This formula gives only the amount of water 

 added beyond the limit fixed by the legal standard 

 and is correct only if the original milk contained the 

 amount of solids-not-fat prescribed by the standard 

 (usually 9 per cent.). Hence, in cases of watered 

 milk, the calculated amount of water added is gener- 

 ally less than the real amount added. 



Example : A milk is found to contain 3 per cent, of 

 fat and to show a lactometer reading of 27. Applying 

 the formula for finding the amount of solids-not-fat, 

 the per cent, is 7.35. If the legal standard for solids- 

 not-fat is 9, then the formula becomes 



the per cent, of added water that is contained in the 

 milk, assuming that it contained 9 per cent, of solids- 

 not-fat before being watered. 



The following rule can also be used: Add together 

 the lactometer reading and the per cent, of fat present 

 in the milk, divide the sum by 36, multiply the result 

 by loo and subtract the last result from 100. Ex- 

 pressed as a formula, this becomes 



Per cent, of | ... lactometer reading + per centof fatv^ 



added water \ m ilk=ioo 3 6 ~ X IO . 



An examination of the serum of milk by means of 

 a refractometer gives, probably, the most reliable 

 means of detecting added water in milk, but this 

 method is available only for special workers. For its 

 details see "Food Inspection and Analysis," by Leach, 

 (P- 139). 



