ADULTERATIONS OF MILK 215 



added without serious danger of detection. If larger amounts of 

 water are added, comparison of the specific gravity, total solids, 

 and plasma solids of the suspected milk with the same factors in 

 normal milk will usually lead to detection. The specific gravity 

 of the sohds also aids in revealing the shortage in cream, inas- 

 much as the solids of whole milk have a lower specific gravity 

 than the solids of skimmed milk, owing to the smaller amount 

 of fat in the latter. Milk has been watered when the specific 

 gravity is below the normal, when the percentage of plasma solids is 

 low, and the specific gravity of the milk solids 1.25 to 1.35. Milk 

 has been skimmed when the specific gravity of both the milk 

 and the total solids is high, the percentage of fat low, and the 

 percentage of plasma solids high. Milk has been both watered 

 and skimmed when the percentage of fat is low, the specific 

 gravity of the total solids normal or above normal, and the specific 

 gravity of the milk either normal or not. 



The lowest percentage of plasma solids permissible has been 

 legally determined in many states and cities. On the basis of 

 such limits. Van Slyke has given formulas for estimating the 

 quantity of water added. However, it should be observed that, 

 since legal standards represent the minimum, the results obtained 

 by these formulas are usually too low. The formulas depend 

 upon the well-known relation of specific gravity, fat, and solids. 

 After the percentage of fat and the specific gravity of the sus- 

 pected milk have been determined, the plasma solids are cal- 

 culated and the amount of water estimated according to the 



formula: 



Per ce nt, of plasma solids X 100 

 Per cent, of added water = 100 - Legal standard for plasma solids 



The following formula may also be used : 



„ ,, , Lactometer reading + per cent, fat ^, ,^„ 



Per cent, of added water = 100 — ^ '^ X 100 



Herz gives the following formulas for estimating the amount 

 of water added, the amount of fat removed by skimming, or both, 

 if both conditions exist : 



Addition of Water 

 The amount of added water contained in 100 parts ^ 100 (ri — n) 

 of watered milk ri 



The amount of water added to the undiluted milk = 



r2 



Skimmed Milk 

 The amount of fat removed from the milk = fi — fz -|- :^ 



