2 MILK AND DAIRY PRODUCTS PART 



The freezing point of milk lies between 0'55 and 0'57C., 

 that is, below that of water. According to J. Winter and E. 

 Parmentier, 1 the freezing-point of milk is almost constant, 

 0*555 C. ; the author 2 also has found that with mixed milk 

 this figure is practically correct. Milk differs from water in 

 having its greatest density at freezing point, whereas that 

 of the latter is, as is well known, at 4 C. 



The boiling point of milk is about 0'2 higher than that of 

 water when both are under the same atmospheric pressure. 



The specific heat of milk varies according to the amount 

 of dry matter it contains, and Fleischmarm 3 gives the average 

 as O9457 compared with water as unity. According to later 

 and more exact investigations by C. Schnorf, 4 the specific heat 

 of milk is higher than this, and on an average reaches T042. 



The refractive index of milk, according to the most recent 

 observations, is between 1'3430 and T3445 at 15 C. The 

 resistance which milk offers to the passage of an electric 

 current has been found to vary considerably by different 

 observers, but F. Petersen, 5 to whom the latest experiments 

 on this subject are due, gives it as varying between 186 and 304 

 ohms at 15 C., with an average of 231'64 ohms. Where 

 the experiments were made with mixed milk the resistance 

 at 15 C, varied between 204 and 255 ohms. 



Milk has an amphoteric reaction, it being both alkaline 

 and acid to litmus paper. This is because milk contains 

 phosphates which have an alkaline reaction, and others that 

 have an acid reaction. 



To phenolphthalein, however, milk is acid, and requires a not 

 inconsiderable amount of alkali in order to bring the liquid to 

 a neutral reaction with this indicator. The quantity of alkali 

 required depends upon the degree of acidity of the milk. If 

 JV/4 alkali is taken for the titration, as recommended by 

 Soxhlet-Henkel, it is found that on an average 7 c.c. are 

 required to neutralise 100 c.c. milk. On the other hand, to 

 make 100 c.c. milk neutral to lacmoid requires, according to 

 Courant, 6 41 c.c. N/10 H 2 S0 4 . 



1 Revue Gen6rale du Lait, Vol. Ill, p. 193. 2 Ibid., Vol. IV, p. 505. 



3 Journal fiir Landwirtschaft, 1902, Vol. L, 33-76. 



4 fievue Gentrale da Lait, Vol. IV, p. 313. 



5 Unfermchnngen nber den eleJctriftch. Widerstand der Milch. Inau^. Diss. 

 Kiel, 1904. e Pfliiger's Arch., Vol. L, 



