as if the superheaters
were not installed. The saving due to the added boiler efficiency that
will be obtained is obvious.

Following the course of the steam in a plant, the next advantage of the
use of superheated steam is the absence of water in the steam pipes. The
thermal conductivity of superheated steam, that is, its power to give up
its heat to surrounding bodies, is much lower than that of saturated
steam and its heat, therefore, will not be transmitted so rapidly to the
walls of the pipes as when saturated steam is flowing through the pipes.
The loss of heat radiated from a steam pipe, assuming no loss in
pressure, represents the equivalent condensation when the pipe is
carrying saturated steam. In well-covered steam mains, the heat lost by
radiation when carrying superheated steam is accompanied only by a
reduction of the superheat which, if it be sufficiently high at the
boiler, will enable a considerable amount of heat to be radiated and
still deliver dry or superheated steam to the prime movers.

It is in the prime movers that the advantages of the use of superheated
steam are most clearly seen.

In an engine, steam is admitted into a space that has been cooled by the
steam exhausted during the previous stroke. The heat necessary to warm
the cylinder walls from the temperature of the exhaust to that of the
entering steam can be supplied only by the entering steam. If this steam
be saturated, such an adding of heat to the walls at the expense of the
heat of the entering steam results in the condensation of a portion.
This initial condensation is seldom less than from 20 to 30 per cent of
the total weight of steam entering the cylinder. It is obvious that if
the steam entering be superheated, it must be reduced to the temperature
of saturated steam at the corresponding pressure before any condensation
can take place. If the steam be superheated sufficiently to allow a
reduction in temperature equivalent to the quantity of heat that must be
imparted to the cylinder walls and still remain superheated, it is clear
that initial condensation is avoided. For example: assume one pound of
saturated steam at 200 pounds gauge pressure to enter a cylinder which
has been cooled by the exhaust. Assume the initial condensation to be 20
per cent. The latent heat of the steam is given up in condensation;
hence, .20 x 838 = 167.6 B. t. u. are given up by the steam. If one
pound of superheated steam enters the same cylinder