serves principally as a mechanical protection for the silk, the
principal insulating properties residing in the silk.

_Enamel_. A later development in the insulation of magnet wire has
resulted in the so-called enamel wire. In this, instead of coating the
wire with some fibrous material such as silk or cotton, the wire is
heated and run through a bath of fluid insulating material or liquid
enamel, which adheres to the wire in a very thin coating. The wire is
then run through baking ovens, so that the enamel is baked on. This
process is repeated several times so that a number of these thin
layers of the enamel are laid on and baked in succession.

The characteristics sought in good enamel insulation for magnet wire
may be thus briefly set forth: It is desirable for the insulation to
possess the highest insulating qualities; to have a glossy, flawless
surface; to be hard without being brittle; to adhere tenaciously and
stand all reasonable handling without cracking or flaking; to have a
coefficient of elasticity greater than the wire itself; to withstand
high temperatures; to be moisture-proof and inert to corrosive
agencies; and not to "dry out" or become brittle over a long period of
time.

_Space Utilization_. The utilization of the winding space in an
electromagnet is an important factor in design, since obviously the
copper or other conductor is the only part of the winding that is
effective in setting up magnetizing force. The space occupied by the
insulation is, in this sense, waste space. An ideally perfect winding
may be conceived as one in which the space is all occupied by wire;
and this would necessarily involve the conception of wire of square
cross-section and insulation of infinite thinness. In such a winding