Scotland/Scots > Memoir of John Elder, engineer and shipbuilder, Glasgow

MEMOIR OF JOHN ELDER.
19
from the principles of thermodynamics was,
that when steam performs work by expan¬
sion a quantity of heat disappears sufficient
not only to lower the temperature of the
steam to that corresponding to its lowered
pressure, but to cause a certain portion of
the steam to pass into the liquid state. The
steam thus spontaneously liquified collects
in the form of water in the cylinder; and if
the cylinder and piston were made of a non¬
conducting material, that water would simply
be discharged from time to time into the con¬
denser, without causing any waste of heat.
But the cylinder and piston, being made of
a conducting material, give out heat to the
liquid water which adheres to them, so as
to re-evaporate it when the communication
with the condenser is opened ; and this heat
is carried off to the condenser with the ex¬
haust-steam, leaving the piston and the inside
of the cylinder at a low temperature, even
though the outside of the cylinder should
be clothed with an absolute non-conductor.
When steam from the boiler is admitted at
the beginning of the next stroke, part of it
is immediately liquified through the expendi-