| Luminous flame.
+-----------+-----------+-------------+----------
| Inner. | Outer. | Inner. | Outer.
+-----------+-----------+-------------+----------
Nitrogen | 75.75 | 79.17 | 77.52 | 69.41
Water vapor | 13.47 | 14.29 | 11.80 | 19.24
Carbon dioxide | 2.99 | 5.13 | 4.93 | 8.38
Carbon monoxide | 3.69 | Nil. | 2.45 | 2.58
Marsh gas | 0.51 | 0.31 | 0.95 | 0.39
Acetylene | 0.04 | Nil. | 0.27 | Nil.
Hydrogen | 3.55 | 0.47 | 2.08 | Nil.
+-----------+-----------+-------------+----------
| 100.00 | 100.00 | 100.00 | 100.00

These figures are of the greatest interest, as they show conclusively
that the extreme top of the Bunsen flame is the only portion of the
flame which can be used for heating a solid substance without
liberating deleterious gases; and this corroborates the previous
experiment on the gases in the outer zone of a flame, which showed
that the outer zone of a Bunsen flame is the only place where complete
combustion is approached.

Moreover, this sets at rest a question which has been over and over
again under discussion, and that is whether it is better to use a
luminous or a non-luminous flame for heating purposes. Using a
luminous flame, it is impossible to prevent a deposit of carbon, which
is kept by the flame at a red heat on its outer surface, and the
carbon dioxide formed by the complete combustion of the carbon already
burned up in flame is reduced by this back to carbon monoxide, so that
even in the extreme tip of a luminous flame it is impossible to heat a
cool body without giving rise to carbon monoxide, although acetylene
being absent, gas stoves, in which small flat flame burners are used,
have not that subtile and penetrating odor which marks the ordinary
atmospheric burner stove, with the combustion checked just at the
right spot for the formation of the greatest volume of noxious
products.

It is the contact of the body to be heated with the flame before
combustion is complete which gives rise to the greatest mischief; any
cooling of the flame extinguishes a portion of the flame, and the
gases present in the flame at the moment of extinction creep along the
cooled surface and