70 Sir H. Davy’s researches on jiame. 
wire of ^ of an inch heated cherry red, will not inflame ole- 
fiant gas, but it will inflame hydrogene gas ; and a wire of 
■J, heated to the same degree, will inflame olefiant gas ; but 
a wire of must be heated to whiteness to inflame hydro- 
gene, though at a low red heat it will inflame bi-phosphuretted 
gas ; but wire of 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 hydrogene 
and oxygene 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 caiv 
not 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 sul- 
phur immediately come through it, and the flame is inter- 
cepted; the fumes continue 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 burn- 
ing immediately upon the surface of the oil : it will be found 
to be about ~ of an inch in diameter. Let a fine iron wire 
of be made into a circle of of an inch in diameter and 
