CHEMICAL REACTION OF MILK 33 



milk was not reliable. The fat-globules themselves are said to be 

 almost transparent, yet the color and opacity of milk is largely 

 due to their presence. This characteristic may perhaps be. 

 explained by assuming that the fat-globules in milk deflect the 

 light instead of allowing it to pass through them. 



After the fat has been removed, the milk still continues to 

 be opaque. When the albuminoid matter has been removed 

 and filtered off the nitrate becomes clear and transparent. 



Chemical Reaction of Milk. Milk when fresh shows an 

 amphoteric reaction, which means that it exhibits both an alkaline 

 and an acid reaction when tested with litmus paper. It turns 

 blue litrrus paper red, and red litmus paper blue. This peculiar 

 behavior of milk is said to be due to the caseous matter in the 

 milk, which itself has an acid reaction, while the remainder of 

 the serum has a slight alkaline reaction. By testing the reaction 

 of fresh milk with a tenth normal alkali solution, and using 

 phenolphthalein as an indicator, an acid reaction is obtained. 

 After standing, milk soon becomes distinctly acid, due to a 

 change of the milk-sugar into acids, chiefly lactic acid, through 

 the action of micro-organisms. Richmond maintains that the 

 amphoteric reaction of milk has acquired a false importance, as he 

 believes that the neutrality, as measured by the action of litmus 

 paper, is not chemical neutrality. 



Specific Gravity of Milk. By specific gravity of milk we 

 mean the weight of the milk as compared to that of an equal 

 volume of water at the same temperature. If a certain volume 

 of water weighs 1000 pounds, an equal volume of milk at the 

 same temperature and under the same conditions will weigh 

 about 1032 pounds. Reducing the figure to a basis of i, as is 

 always done, the comparison between the two equal volumes of 

 water and milk will be i and 1.032. This latter figure represents 

 the average specific gravity of normal milk. 



It can be readily seen that the correct specific gravity can 

 be obtained only at one given temperature, for, as the tempera- 

 ture of the substance becomes higher, the density of it grows less, 

 and consequently the specific gravity will be less. The tempera- 

 ture at which the lactometers are standardized is 60 F. 



