The by-product from the belting bull, which is about fifty per cent, is used for shoe leather and leather straps. There is considerable leather taken from the belting bull for certain harness work. The belly is thick and porous though not tough, and is used for halters, cow bridles, and other parts of harness where the strain is not great.
Round belt is made from the best belting, but while the strain on round belting is not severe, the leather must be soft and pliable. It is selected from regular stock of native steer hide.
Leather that has been tanned is made up of a great many little bundles of fibers. The coarser and stronger fibers are on the inside, and the very fine and smoothly laid fibers are on the outside. These fibers are so intertwined and so elastic that when the leather bends these bundles play on one another. On account of the smoothness of the surface it may be polished, and beautiful finishes and effects obtained on the leather.
The elasticity of leather (which is due to the elasticity of its fibers) allows it to stretch to a great extent. The tendency to return to its original position is very strong at the beginning, but grows weaker if the strain is continued at any one point. Of course, in stretching the leather, there is always a corresponding drawing in another part of the shoe, which gives it a worn and baggy appearance.
When shoes are removed from the feet, they are oftentimes damp, due to perspiration. The stretched or strained fibers are apt to shrink and return to their original position. In order to avoid this, it is necessary to place shoe-trees in them.
When the linings of shoes are exposed to friction and excretion of perspiration from the feet of some people, they deteriorate. This is due to the fact that the acids of perspiration (acetic, formic and butyric acids) have become so concentrated that they act on the fibers of the leather. These acids exert a burning effect, causing the fibers to lose their elasticity so that they no longer play on one another, but become fastened to each other. The result is that they become hard, and any attempt to bend the leather tears them apart; and once the union of fibers is destroyed it cannot be repaired.