is forced into the flame, a greater heat and more active burning follows.
If the amount of air, and consequently oxygen, is reduced, the flame
becomes smaller and weaker and the combustion is less rapid. A flame may be
easily extinguished by shutting off all of its air supply.

The oxygen of the combustion only forms one-fifth of the total volume of
air; therefore, if we were to supply pure oxygen in place of air, and in
equal volume, the action would be several times as intense. If the oxygen
is mixed with the fuel gas in the proportion that burns to the very best
advantage, the flame is still further strengthened and still more heat is
developed because of the perfect combustion. The greater the amount of fuel
gas that can be burned in a certain space and within a certain time, the
more heat will be developed from that fuel.

The great amount of heat contained in acetylene gas, greater than that
found in any other gaseous fuel, is used by leading this gas to the
oxy-acetylene torch and there combining it with just the right amount of
oxygen to make a flame of the greatest power and heat than can possibly be
produced by any form of combustion of fuels of this kind. The heat
developed by the flame is about 6300 Fahrenheit and easily melts all the
metals, as well as other solids.

Other gases have been and are now being used in the torch. None of them,
however, produce the heat that acetylene does, and therefore the
oxy-acetylene process has proved the most useful of all. Hydrogen was used
for many years before acetylene was introduced in this field. The
oxy-hydrogen flame develops a heat far below that of oxy-acetylene, namely
4500 Fahrenheit. Coal gas, benzine gas, blaugas and others have also been
used in successful applications, but for the present we will deal
exclusively with the acetylene fuel.