CoMPOSITION AND PRovrkRTIES OF MILK Powbrrs 325 
called solution is a factor which does not always depend on their 
actual solubility. 
Other conditions being the same, it is obvious that the finer the 
particles of the powder the more rapidly will it dissolve. This fact 
is based on the well-known physical law that the smaller a body the 
larger is its surface in proportion to its cubic contents. The sur- 
faces of two spheres are to each other as the squares of their diame- 
ters and the cubic contents of two spheres are to each other as the 
cubes of their diameters. This is clearly demonstrated in the fol- 
lowing example: 
One sphere has a diameter of 2 inches and the other sphere has 
a diameter of 4 inches. The surfaces and the cubic contents of 
these spheres are as follows: 
Pig. 108. 
Sphere with Sphere with 
2-inch dia. 4-inch dia. 
Surfaces == 2x24 4x4= 16 
Cubic contents =2«2«K2=8 4x4«4= 64 
The surface of the sphere with the 4-inch diameter is four 
times as large as the surface of the sphere with the 2-inch diameter. 
But the cubic content of the sphere with the 4-inch diameter is 
eight times as great as the cubic content of the sphere with the 2-inch 
diameter. 
And again, the cube and circular shape of a body has a smaller 
surface than the oblong and flake shape body. 
The greater the area or surface of a body with a given cubic 
content, the more surface is exposed to the solvent and the more 
rapidly will it dissolve. Therefore, the finer and more flaky the 
particles of milk powder, the more readily and more rapidly will 
they dissolve. 
The spray-process powders usually are finer and more flaky 
