| 15.73| 14.07| 15.47| 13.34|
| Pound of Oil | | | | | | | |
| | | | | | | | |
| Per Cent of | | | | | | | |
| Rated Capacity | Pounds | 113.6| 172.9| 108.6| 193.8| 104.9| 207.1|
| Developed | | | | | | | |
| | | | | | | | |
| B. t. u. per | | | | | | | |
| Pound of Oil | B. t. u. | 18626| 18518| 18326| 18096| 18600| 18600|
| | | | | | | | |
| Efficiency | Per Cent | 83.15| 79.46| 83.29| 76.02| 80.70| 69.6 |
|__________________|__________|______|______|______|______|______|______|

Burning Oil in Connection with Other Fuels--Considerable attention has
been recently given to the burning of oil in connection with other
fuels, and a combination of this sort may be advisable either with the
view to increasing the boiler capacity to assist over peak loads, or to
keep the boiler in operation where there is the possibility of a
temporary failure of the primary fuel. It would appear from experiments
that such a combination gives satisfactory results from the standpoint
of both capacity and efficiency, if the two fuels are burned in separate
furnaces. Satisfactory results cannot ordinarily be obtained when it is
attempted to burn oil fuel in the same furnace as the primary fuel, as
it is practically impossible to admit the proper amount of air for
combustion for each of the two fuels simultaneously. The Babcock &
Wilcox boiler lends itself readily to a double furnace arrangement and
Fig. 30 shows an installation where oil fuel is burned as an auxiliary
to wood.

[Illustration: Fig. 30. Babcock & Wilcox Boiler Set with Combination Oil
and Wood-burning Furnace]

Water-gas Tar--Water-gas tar, or gas-house tar, is a by-product of the
coal used in the manufacture of water gas. It is slightly heavier than
crude oil and has a comparatively low flash point. In burning, it should
be heated only to a temperature which makes it sufficiently fluid, and
any furnace suitable for crude oil is in general suitable for water-gas
tar. Care should be taken where this fuel is used to install a suitable
apparatus for straining it before it is fed to the burner.

[Illustration: Babcock & Wilcox Bo