Some new Researches on Flame. 19 
heated even to whiteness will not inflame mixtures of fire- 
damp. 
These circumstances will explain, why a mesh of wire so much 
finer is required to prevent the explosion from hydrogen and 
oxygen from passing, and why so coarse a texture and wire is 
sufficient to prevent the explosion of the fire-damp, fortunately 
the least combustible of the known inflammable gases. 
The general doctrine of the operation of wire-gauze cannot 
be better elucidated than in its effects upon the flame of sulphur. 
When wire-gauze of 600 or 700 apertures to the square inch is 
held over the flame, fumes of condensed sulphur immediately 
come through it, and the flame is intercepted; the fumes con- 
tinue for some instants, but as the heat increases they diminish ; 
and at the moment they disappear, which is long before the gauze 
becomes red hot, the flame passes; the temperature at which 
sulphur burns being that at which it is gaseous. 
Another very simple illustration of the truth of this view is 
offered in the effect of the cooling agency of metallic surfaces 
upon very small flames. Let the smallest possible flame be made 
by a single thread of cotton immersed in oil, and burning im- 
mediately upon the surface of the oil; it will be found to be 
about 1-30th of an inch in diameter. Let a fine iron wire of 
1-180th be made into a circle of 1-10th of an inch in diameter, 
and brought over the flame. Thongh at such a distance, it will 
instantly extinguish the flame, if it be cold: but if it be held above 
the flame, so as to be slightly heated, the flame may be passed 
through it without being extinguished. That the effect depends 
entirely upon the power of the metal to abstract the heat of 
flame, is shown by bringing a glass capillary ring of the same 
diameter and size over the flame ; this being a much worse con- 
ductor of heat, will not extinguish it even when cold, If its 
size however be made greater, and its circumference smaller, it 
will act like the metallic wire, and require to be heated to pre- 
vent it from extinguishing the flame*. 
Suppose a flame divided by the wire-gauze into smaller flames, 
each flame must be extinguished in passing its aperture till that 
aperture has attained a temperature sufficient to produce the 
permanent combustion of the explosive mixture. 
A flame of sulphur may be made much smaller than that of 
hydrogen, that of hydrogen smaller than that of a wick fed with 
* Let a small giobe of metal 1-20th of an inch in diameter made b 
fusing the end of a wire be bronght near a flame of 1-30th in diameter, it 
will extinguish it when cold at the distance of its own diameter; let it be 
heated, and the distance will diminish at which it produces the extinction; 
and at a white heat it does not extinguish it by actual contact, though at a 
dull red heat it immediately produces the effect. 
B2 
oil, 
