explosive mixtures confined by wire-gauze , &e. 117 
appear in the centre of the other flame, proving that there is 
oxygene even in its interior part. 
The heat communicated by flame must depend upon its 
mass ; this is shown by the fact that the top of a slender 
cylinder of wire-gauze hardly ever becomes dull red in the 
experiment on an explosive mixture, whilst in a larger cylin- 
der, made of the same material, the central part of the top 
soon becomes bright red. A large quantity of cold air thrown 
upon a small flame, lowers its heat beyond the explosive 
point, and in extinguishing a flame by blowing upon it, the 
effect is probably principally produced by this cause, assisted 
by a dilution of the explosive mixture. 
If a piece of wire-gauze sieve is held over a flame of a lamp 
or of coal gas, it prevents the flame from passing it, and the 
phenomenon is precisely similar to that exhibited by the wire- 
gauze cylinders ; the air passing through is found very hot, 
for it will convert paper into charcoal ; and it is an explosive 
mixture, for it will inflame if a lighted taper is presented to 
it, but it is cooled below the explosive point by passing through 
wires even red hot, and by being mixed with a considerable 
quantity of air comparatively cold. The real temperature of 
visible flame is perhaps as high as any we are acquainted with. 
Mr. Tennant was in the habit of showing an experiment, 
which demonstrates the intensity of its heat. He used to fuse 
a small filament of platinum in the flame of a common candle; 
and it is proved by many facts, that a stream of air may 
be made to render a metallic body white hot, yet not be itself 
luminous. 
A considerable mass of heated metal is required to inflame 
