....................pounds
35 Equivalent evaporation from and at 212 degrees per pound
of combustible [Item 21/(Item 16-Item 17)]......................pounds

EFFICIENCY

36 Calorific value of one pound of dry coal.........................B. t. u.
37 Calorific value of one pound of combustible......................B. t. u.

( Item 34x970.4)
38 Efficiency of boiler, furnace and grate (100 x -------------)....per cent
( Item 36 )

( Item 35x970.4)
39 Efficiency of boiler and furnace (100 x -------------)...........per cent
( Item 37 )

COST OF EVAPORATION

40 Cost of coal per ton of......pounds delivered in boiler room......dollars
41 Cost of coal required for evaporating 1000 pounds of water
from and at 212 degrees........................................dollars

[Illustration: Portion of 3600 Horse-power Installation of Babcock &
Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at
the Loomis Street Plant of the Peoples Gas Light & Coke Co., Chicago,
Ill. This Company has Installed 7780 Horse Power of Babcock & Wilcox
Boilers]

THE SELECTION OF BOILERS WITH A CONSIDERATION OF THE FACTORS DETERMINING
SUCH SELECTION

The selection of steam boilers is a matter to which the most careful
thought and attention may be well given. Within the last twenty years,
radical changes have taken place in the methods and appliances for the
generation and distribution of power. These changes have been made
largely in the prime movers, both as to type and size, and are best
illustrated by the changes in central station power-plant practice. It
is hardly within the scope of this work to treat of power-plant design
and the discussion will be limited to a consideration of the boiler end
of the power plant.

As stated, the changes have been largely in prime movers, the steam
generating equipment having been considered more or less of a standard
piece of apparatus whose sole function is the transfer of the heat
liberated from the fuel by combustion to the steam stored or circulated
in such apparatus. When the fact is considered that the cost of steam
generation is roughly from 65 to 80 per cent of the total cost of power
production, it may be readily understood that the most fruitful field
for improvement exists