en made, they should be
used as a basis for study with the idea of improving the boiler
performance.

Take the matter of boiler efficiency, for example, as found from
the test mentioned. Its value was 54 per cent. This is altogether
too low and indicates wasteful operation. The efficiency of a
hand-fired boiler ought not to be less than 65 per cent, and it can
be increased to 70 per cent by careful management under good
conditions.

The chart in figure 3 can be used to indicate the evaporation that
should be obtained in order to reach a desired efficiency. Suppose,
for example, that it is desired to know how much water per pound of
coal must be evaporated to produce a boiler efficiency of 65 per
cent with coal having a heating value of 13,500 B. t. u. per pound.

Locate 13,500 at the bottom of the chart, follow the vertical line
until it meets the diagonal marked 65 per cent, and then from this
point follow the horizontal line to the left-hand edge, where the
figure 9 is found. This means that the equivalent evaporation from
and by 212 deg. F. per pound of coal must be 9 pounds of water. If the
steam pressure is 100 pounds gauge, and the feed-water temperature
is 180 deg. F. the factor of evaporation is 1.0727, then the actual
evaporation must be 9 / 1.0727 = 8.36 pounds per pound of coal. In
other words, to increase the efficiency from 54 per cent to 65 per
cent under the same conditions of pressure and feed-water
temperature, it would be necessary to increase the actual
evaporation from 7 pounds to 8.36 pounds. This would mean
practically 20 per cent more steam from the same weight of coal
used.

[Illustration: _Heating Value of Coal, in B. t. u. Per Pound_

FIG. 3.]

How to do this will require some study and experimenting on the
part of the fireman or engineer. The three most common reasons for
low-boiler efficiency are (1) excess air, (2) dirty heating
surfaces, and (3) loss of coal through the grates. _The first of
these items is the most important of the three._ In most cases the
greatest preventable waste of coal in a boiler plant is directly
due to excess air. Excess air simply means the amount of air which
gets into the furnace and boiler which is not needed for completing
the combustion of the coal. Very often twice as much air is
admitted to the boiler setting as is required. This extra or excess
air is heated and carries heat out through the chimney instead of
heating the water in the boiler to ma