If there is any preference, it may be
given to illuminating flames, as the proportion of radiant heat is
greater, and this makes the average temperature of the inclosed space
more equal; but on the other hand, may be considered the greater
liability of the very fine holes, necessary for illuminating flames, to
be choked with dust and dirt. This may, to a great exent, be obviated
by using very small union jets, and setting them horizontally, so as
to make a flat horizontal sheet of flame. Burners placed this way are
practically safe from the interference of falling dust or dirt, but not
from splashes. Falling dirt or splashes must always be considered in the
arrangement of any burners, and the ventilation must be no greater than
is absolutely necessary for the required work. In cooking, this limit
of ventilation may be exceeded, as most things are better cooked with a
free ventilation, the extra cost of fuel being well compensated for by
the better quality of the result.
The air in an oven or inclosed space heated by flames inside is similar
in character to highly superheated steam.
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