Specific Gravity of Milk. 



dition of alkalies to milk free of fat renders it transparent. Ham- 

 marsten furnished the proof that a calcium caseinate solution which 

 corresponds to the composition of milk is almost as non-trans- 

 parent as milk. The milk becomes less transparent the smaller the 

 fat globules are. This is most strikingly apparent when the fat 

 globules are broken up to dust-sized bodies (for instance through 

 homogenization). The appearance of fresh milk is also influenced 

 by the coloring matter present in the milk plasma and in the fat. 

 It is known that the skimmed milk of certain cows varies considera- 

 bly in color ; at times it is bluish white, sometimes more yellowish 

 green, again transparent, other times of a non-transparent whitish 

 color, and also the fat has a more yellow color during the pasturing 

 of the animals than at the time of stable feeding. 



The non-transparency as mentioned above is no proof of the presence of fat in 

 the milk; therefore all methods which are destined to establish the quantity of fat or 

 addition of water by the establishment of the whiteness, are of no use, as for instance, 

 Heeren's pioscope, Feser's lactoscope, etc. 



If milk is allowed to stand for a time, cream forms on the 

 surface ; the fat globules rise and collect usually as a distinct layer 

 of cream above the milk. The rapidity of the separation depends 

 on the temperature, the size of the fat globules, and the density of 

 the milk plasma. The quantity of the cream is not in parallel rela- 

 tion to the quantity of fat ; it depends on the size of the fat globules. 



The separation of cream may be hastened and increased by 

 centrifugalization. During separation while allowing to stand, 

 about 85% of the fat rises to the surface, while by a perfectly 

 operating centrifuge the separation of cream may be accomplished 

 up to 0. 01% of its fat. 



The specific gravity of the milk depends on the solid sub- 

 stances, the relation of the mixture and the condition of the sus- 

 pended, dissolved, and emulsified constituents of the solid sub- 

 stances. Corresponding to the variable composition of cow's milk 

 it is natural that the specific gravity of the milk should vary. 

 It fluctuates considerably, varying from 1.027 to 1.034 at a 

 temperature of 15 deg. Similar to the impossibility of speaking of 

 milk of normal composition, one cannot speak of milk of normal 

 specific gravity, and even to give average figures would be of very 

 problematical value; but to take such average figures or even 

 smallest values as a basis for the calculation of falsification would 

 be a gross error. Milk from many cows would under ordinary con- 

 ditions have a specific gravity of 1,029 to 1,033. 



The specific gravity is measured, or is calculated from the 

 values of fat contents and solids, according to formulas, which, 

 depending on the milk from certain breeds, or certain localities, 

 show slight variations. This formula made on the basis of the 

 value of the specific gravity of the milk fat (about 0.93), and the 

 solids or dry substances (1.6001), which is quite constant, is 

 according to Fleischmann : 



