lts
before you.

If a cold substance, metal or non-metal, be placed in a flame, whether
it be luminous or non-luminous, it will be observed that there is a
clear space, in which no combustion is taking place, formed round the
cool surface, and that as the body gets heated so this space gets less
and less until, when the substance is at the same temperature as the
flame itself, there is contact between the two. Moreover, when a
luminous flame is employed in this experiment the space still exists
between the cool body and the flame, but you also notice that the
luminosity is decreased over a still larger area although the flame
exists.

This meaning that, in immediate contact with the cold body, the
temperature is so reduced that the flame cannot exist, and so is
extinguished over a small area; while over a still larger space the
temperature is so reduced that it is not hot enough to bring about
decomposition of the heavy hydrocarbons with liberation of carbon to
the same extent as in hotter portions of the flame. Now, inasmuch as
when water is heated or boiled in an open vessel, the temperature
cannot rise above 100 deg.C., and as the temperature of an ordinary flame
is over 1,000 deg.C., it is evident that the burning gas can never be in
contact with the bottom of the vessel, or, in other words, the gas is
put out before combustion is completed, and the unburned gas and
products of incomplete combustion find their way into the air and
render it perfectly unfit for respiration.

The portion of the flame which is supposed to be the hottest is about
half an inch above the tip of the inner zone of the flame, and it is
at this point that most vessels containing water to be heated are made
to impinge on the flame; and it is this portion of the flame, also,
which is utilized for raising various solids to a temperature at which
they radiate heat.

In order to gain an insight into the amount of contamination which the
air undergoes when a geyser or cooking stove is at work, I have
determined the composition of the products of combustion, and the
unburned gases escaping when a vessel containing water at the ordinary
temperatures is heated up to the boiling point by a gas flame, the
vessel being placed, in the first case, half an inch above the inner
cone of the flame, and in the second, at the extreme outer tip of the
flame.

GASES ESCAPING DURING CHECKED COMBUSTION.

| Bunsen flame.