be done close to the boiler to
minimize radiation loss. If the temperature is raised to a point where
an appreciable vaporization occurs, the oil will flow irregularly from
the burner and cause the flame to sputter.

On both steam and air atomizing types, a by-pass should be installed
between the steam or air and the oil pipes to provide for the blowing
out of the oil duct. Strainers should be provided for removing sludge
from the fuel and should be so located as to allow for rapid removal,
cleaning and replacing.

Mechanical burners have been in use for some time in European countries,
but their introduction and use has been of only recent occurrence in the
United States. Here as already stated, the means for atomization are
purely mechanical. The most successful of the mechanical atomizers up to
the present have been of the round flame type, and only these will be
considered. Experiments have been made with flat flame mechanical
burners, but their satisfactory action has been confined to instances
where it is only necessary to burn a small quantity of oil through each
individual burner.

This system of oil burning is especially adapted for marine work as the
quantity of steam for putting pressure on the oil is small and the
condensed steam may be returned to the system.

The only method by which successful mechanical atomization has been
accomplished is one by which the oil is given a whirling motion within
the burner tip. This is done either by forcing the oil through a passage
of helical form or by delivering it tangentially to a circular chamber
from which there is a central outlet. The oil is fed to these burners
under a pressure which varies with the make of the burner and the rates
at which individual burners are using oil. The oil particles fly off
from such a burner in straight lines in the form of a cone rather than
in the form of a spiral spray, as might be supposed.

With burners of the mechanical atomizing design, the method of
introducing air for combustion and the velocity of this air are of the
greatest importance in securing good combustion and in the effects on
the character and shape of the flame. Such burners are located at the
front of the furnace and various methods have been tried for introducing
the air for combustion. Where, in the spray burners, air is ordinarily
admitted through a checkerwork under the burner proper, with the
mechanical burner, it is almost universally admitted around t