ADHESION OF MILK 37 



The completeness of natural skimming is to a certain extent 

 based upon the mathematical law which is stated as follows: 

 " The surfaces of two spheres are to each other as the squares, of 

 their diameters, and their cubical contents are to each other 

 as the cubes of their diameters." The larger the globules are, 

 the greater the surface is, and the greater the resisting force to 

 which they are subjected. From the law stated it can be seen 

 that as the size of the globule increases, the cubical content 

 increases more rapidly than the surface. If a fat-globule were 

 split up into smaller ones, there would be more surface exposed 

 to the serum than was the case while the fat was present in one 

 globule. 



For illustration, suppose two globules of fat to have diameters 

 of 4 and 2 inches respectively. The squares would be 16 inches 

 and 4 inches respectively; their cubes would be 64 inches and 8 

 inches respectively. It will thus be seen, according to the 

 law quoted above, that the larger globule has a surface only four 

 times as great as that of the smaller one ; but the cubical content 

 of the larger globule is eight times that of the smaller one. This 

 illustrates why the large globules rise in cream more quickly than 

 the small ones. In this particular instance the upward force the 

 larger globule is subjected to is eight times greater than that of 

 the smaller one, while the resistant force is only four times as 

 great as that of the small one. 



Adhesion of Milk. Normal sweet milk adheres to wood, 

 glass, and metals to a greater extent than does water. Whole 

 milk has greater adhesive properties than skimmed milk. A 

 paper moistened with milk or cream makes a label that will stick 

 to any dry object; the same paper moistened with skimmed 

 milk has less adhesive power. The adhesive properties of milk 

 are also due to the condition of the nitrogenous matter. This 

 fact is made use of in painting and whitewashing. Slaked lime, 

 when mixed with buttermilk, or milk of any kind, gives a white- 

 wash which will remain on objects much longer than that made 

 by mixing with water. 



Viscosity of Milk. Milk is more viscous than water. The 

 degree of viscosity of fresh milk varies chiefly with the tempera- 



