42 Biological, Chemical and Physical Characteristics of Milk. 



1000 



B== 



10003.75 (d 1.2 f) 



In these equations s stands for specific gravity, d for dry 

 substances or solids, and f for fat. 



The following values may also be calculated from the fat con- 

 tents of the milk and its specific gravity. 



1. Total solids: 



d=1.2f+2.665X 100s - 10 



s 



2. The fat-free solids are shown by deducing the percentage 

 of fat from the percentage of the total solids. 



3. The specific gravity of the solids 



sXd _ 

 " sXd (100 s 100) 



4. Finally the fat contents when the solids and specific grav- 

 ity are known: 



The values obtained from formulas are of course not abso- 

 lutely correct, but represent the results only approximately with 

 the analytical methods of weights, the fat-free dry substance of the 

 milk is not of absolute constant composition, but varies, so that its 

 specific gravity which is based upon the sugars, proteids and salts, 

 varies more or less from the number which has been accepted by 

 Fleischmann as the average value (1.60). 



The equations hold only for cow's milk. 



If milk is freshly drawn, and immediately tested it shows a 

 considerably lower specific gravity (0.0008-0.0015), than after 

 cooling. The milk "contracts" and becomes constant in its specific 

 gravity only after standing for several hours. The cause of this 

 manifestation is not yet entirely clear. Toyonaga aims to explain 

 it by the fixing of previously uncooled and fluid fat globules, which 

 is the most plausible explanation ; other authors believe that the 

 contraction is the result of a cessation of the expansion of the 

 casein. 



The density of the milk varies in accordance with the tempera- 

 ture. The maximum (for water at 4 deg.) lies almost near its 

 freezing point, namely at . 3 deg. C. 



The freezing point of milk is somewhat lower, namely . 54 

 to . 57 deg. This is especially influenced by the presence of salt, 

 less by the sugar contents of the individual samples of milk, and 

 it is induced by the relatively constant amount of soluble salts 

 in the salt contents, which is subject to only slight fluctuations in 

 the milk of healthy animals. 



For the sake of completeness the electrical conductibiiity of 

 the milk should also be mentioned. This varies according to the re- 

 sistance which is offered by the fluid to the current. It fluctuates 



