in the boiler end of the power plant. The
efficiency of the plant as a whole will vary with the load it carries
and it is in the boiler room where such variation is largest and most
subject to control.

The improvements to be secured in the boiler room results are not simply
a matter of dictation of operating methods. The securing of perfect
combustion, with the accompanying efficiency of heat transfer, while
comparatively simple in theory, is difficult to obtain in practical
operation. This fact is perhaps best exemplified by the difference
between test results and those obtained in daily operation even under
the most careful supervision. This difference makes it necessary to
establish a standard by which operating results may be judged, a
standard not necessarily that which might be possible under test
conditions but one which experiment shows can be secured under the very
best operating conditions.

The study of the theory of combustion, draft, etc., as already given,
will indicate that the question of efficiency is largely a matter of
proper relation between fuel, furnace and generator. While the
possibility of a substantial saving through added efficiency cannot be
overlooked, the boiler design of the future must, even more than in the
past, be considered particularly from the aspect of reliability and
simplicity. A flexibility of operation is necessary as a guarantee of
continuity of service.

In view of the above, before the question of the selection of boilers
can be taken up intelligently, it is necessary to consider the subjects
of boiler efficiency and boiler capacity, together with their relation
to each other.

The criterion by which the efficiency of a boiler plant is to be judged
is the cost of the production of a definite amount of steam. Considered
in this sense, there must be included in the efficiency of a boiler
plant the simplicity of operation, flexibility and reliability of the
boiler used. The items of repair and upkeep cost are often high because
of the nature of the service. The governing factor in these items is
unquestionably the type of boiler selected.

The features entering into the plant efficiency are so numerous that it
is impossible to make a statement as to a means of securing the highest
efficiency which will apply to all cases. Such efficiency is to be
secured by the proper relation of fuel, furnace and boiler heating
surface, actual operating conditions, which allow the appro