It must be remembered also that only a
gas yields a flame when it is burnt; the flame of a paraffin lamp and of
a candle is due to the combustion of the vaporised fuel. Methods of
burning acetylene under the mantle are discussed in Chapter IX.; here
only self-luminous flames are being considered, but the theoretical
question of heat economy applies to both processes.
Heat may be lost from a flame in three several ways: by direct radiation
and conduction into the surrounding air, among the products of
combustion, and by conduction into the body of the burner. Loss of heat
by radiation and conduction to the air will be the greater as the flame
exposes a larger surface, and as a more rapid current of cold air is
brought into proximity with the flame. Loss of heat by conduction, into
the burner will be the greater as the material of which the burner is
constructed is a better conductor of heat, and as the mass of material in
that burner is larger. Loss of heat by passage into the combustion
products will also be greater as these products are more voluminous; but
the volume of true combustion products from any particular gas is a fixed
quantity, and since these products must leave the flame at the
temperature of that flame--where the highest temperature possible is
requisite--it would seem that no control can be had over the quantity of
heat so lost.
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