30 CONSTITUENTS OF MILK 



Although milk contains considerable quantities of water 

 (85-90 per cent), the maximum density is found at a tempera- 

 ture near to the freezing point and not at 4° C. as in the case of 

 water. The changes in the volume of milk due to temperature 

 alterations are somewhat variable, being dependent upon the 

 composition; the preceding table, due to Richmond, shows the 

 expansion in glass of milk containing 3.8 per cent of fat and 

 having a density of 1032.0. 



The viscosity of milk, according to Taylor,^^ is not pro'por- 

 tional to the percentage of total solids, but is a function of the 

 fat and the soUds-not-fat content. He found that the relation 

 is expressed by the formula: 



,. , ^ - , (viscosity— fat percentage X 0.0665) 

 percentage solids-not-fat = ^ oTtt ' 



and that the viscosity temperature coeflScient was 



ni = y+0.00723«-0.000156«2. 



Taylor's determinations of the viscosity of milk raised from 20° 

 to 60° C. and subsequently cooled, support the hypothesis of 

 Richmond regarding the explanation of Recknagel's phenome- 

 non. Weigner^^ found that homogenisation of milk slightly 

 increased the viscosity. Two samples having viscosities of 

 1.941 and 1.862, as determined with an Oswald viscosimeter, 

 were increased by homogenisation to 1.967 and 1.889, respec- 

 tively. Weigner thought that this was caused by increased 

 adsorption, especially of caseinogen. 



The freezing point of milk is slightly lower than that of water, 

 being usually —0.54 to —0.57° C. and is especially influenced 

 by the mineral content other than that associated with the 

 caseinogen. As the salts are not subject to wide variation in 

 the milk of healthy cattle, the freezing point is usually fairly 

 constant. This forms the basis of the cryoscopic methods for 

 the detection of milk adulteration. Aitkens^'^ shows that a 

 consideration of the osmotic pressure of the blood of animals 

 and that of the milk secreted points to the conclusion that the 



