112 Testing Milk and Its Products. 



~ t 100 s-100 



s 



S being the sp. gr. of the milk solids, s that of the milk and t 

 the total solids of the milk. 



Example: A sample of milk has been found to contain 13.0 

 per cent, of solids, sp. gr. 1.032; then a ^-||~ 1 -^=3.101; 

 13.03.101=9.899; - 1 -^- =1.31r=the specific fltvity ol the milk 



9-899 ^ 



solids. 



The specific gravity of the solids does not change if ^he milk 

 is watered, while it is increased when the milk is skimmed. If *a 

 sample of milk of the composition given in the preceding e^.- 

 ample had been watered so as to reduce the solids to 11.7 per 

 cent, and .the specific gravity to 1.0291 (as would be the case 

 when 10 per cent, of water was added), we would again have, 

 by calculation as above, S=1.31. If, on the other hand, the 

 milk was skimmed so as to reduce the solids to 11.7 per cent., 

 thereby increasing the specific gravity of the milk to, say 1.035, 

 we would have by substituting these values in the preceding 

 formula, S=1.41, showing conclusively that the milk had been 

 skimmed. 



An addition of skim milk to whole milk would have the same 

 effect as skimming, as regards the composition of the latter, and 

 the specific gravity of its solids. 



The specific gravity of pure butter fat at 60 F. is .93, and 

 of the fat-free milk solids, 1.5847 (Fleischmann). The solids of 

 skim milk have a specific gravity of 1.56. Samples of whole 

 milk, the solids of which have a specific gravity above 1.34 are 

 suspicious, and a specific gravity over 1.40 is conclusive evidence 

 of skimming. 



To facilitate the calculation of the specific gravity of milk 

 solids, Table IV is given in the Appendix, showing at a glance 

 the value of 1 8 ~ 1 for specific gravities between 1.019 and 

 1.0369. An example will readily illustrate the use of the table. 



Example: A* sample of milk has a specific gravity of 1.0343 

 and contains 12.25 per cent, solids. In Table IV, we find in the 

 horizontal line beginning with 1.034 under the column headed 

 0.0003, the figure 3.316, which is the value for 10 8 ~ 100 when 



