8 MARKET DAIRYING 



it is both acid and alkaline. This double reaction is due 

 largely to acid and alkaline salts and possibly to small 

 quantities of organic acids. 



Milk has an average normal specific gravity of 1.032, 

 with extremes rarely exceeding 1.029 ^ri^ ^-^SS- After 

 standing a few moments it loses its homogenous character. 

 Evidence of this we have in the "rising of the cream." 

 This is due to the fact that milk is not a perfect solution 

 but an emulsion. All of the fat, the larger portion of the 

 casein, and part of the ash are in suspension. 



In consistency milk is slightly more viscous than water, 

 the viscosity increasing with the decrease in temperature. 

 It is also exceedingly sensitive to odors, possessing great 

 absorption properties. This teaches the necessity of plac- 

 ing milk in clean pure surroundings. 



Chemical Composition. The composition of milk is 

 very complex and variable, as will be seen from the fol- 

 lowing figures: 



Average Composition of Normal Milk. A com- 

 pilation of figures from various American Ex- 

 periment Stations. 



Water ^y.if 



Butter fat ^3.9^ 



Casein 2.9!^ 



Albumen 5* 



Sugar 4.9)* 



Ash 7!^. 



Fibrin Trace. 



Galactase Trace. 



100. oJ< 



The great variations in the composition of milk are 

 shown by the figures from Koenig, given below : 



