fire-damp requires a very strong heat for its inflammation; that azote and
carbonic acid, even in very small proportions, diminished the velocity of
the inflammation; that mixtures of the gas would not explode in metallic
canals or troughs, where their diameter was less than one-seventh of an
inch, and their depth considerable in proportion to their diameter; and
that explosions could not be made to pass through such canals, or through
very fine wire sieves, or wire gauze. The consideration of these facts
led Sir Humphry to adopt a lamp, in which the flame, by being supplied
with only a limited quantity of air should produce such a quantity of
azote and carbonic acid as to prevent the explosion of the fire-damp, and
which, by the nature of its apertures for giving admittance and egress to
the air, should be rendered incapable of communicating any explosion to
the external air. These requisites were found to be afforded by air-tight
lanterns, of various constructions, supplied with air from tubes or
canals of small diameter, or from apertures covered with wire-gauze,
placed below the flame, through which explosions cannot be communicated;
and having a chimney at the upper part, for carrying off the foul air.
Sir Humphry soon afterwards found that a constant flame might be kept up
from the explosive mixture issuing from the apertures of a wire-gauze
sieve. He introduced a very small lamp in a cylinder, made of wire-gauze,
having six thousand four hundred apertures in the square inch. He closed
all apertures except those of the gauze, and introduced the lamp, burning
brightly within the cylinder, into a large jar, containing several quarts
of the most explosive mixture of gas from the distillation of coal and
air; the flame of the wick immediately disappeared, or rather was lost,
for the whole of the interior of the cylinder became filled with a feeble
but steady flame of a green colour, which burnt for some minutes, till it
had entirely destroyed the explosive power of the atmosphere. This
discovery led to a most important improvement in the lamp, divested the
fire-damp of all its terrors, and applied its powers, formerly so