LAMPS AND CANDLES.
Q. _Of what are OIL, TALLOW, and WAX composed?_
A. Principally of carbon and hydrogen gas. The _solid_ part is carbon,
the _volatile_ part is gas.
Q. _What is CARBON?_
A. A solid substance, generally of a black colour; well known under the
forms of charcoal, lamp-black, coke, black-lead, &c.
Q. _What is HYDROGEN GAS?_
A. The principal ingredient of water. It is well known in the form of
common _coal gas_: it burns so readily that it used to be called
"inflammable air."[10]
[10] To make hydrogen gas, see p. 34.
Q. _Why does a CANDLE BURN when lighted?_
A. The heat of the lighted wick _decomposes the tallow_ into its
elementary parts of carbon and hydrogen; and the _hydrogen of the
tallow_, combining with the _oxygen of the air_, produces _flame_.
Q. _Why is the FLAME of a candle HOT?_
A. 1st--Because the flame liberates _latent heat_ from the air and
tallow: and
2ndly--It throws into _rapid motion_ the _atoms of matter_.
Q. _How is LATENT HEAT liberated by the flame of a CANDLE?_
A. When the _hydrogen_ of the tallow and _oxygen_ of the air _combine_,
they _condense into water_; and much of their latent heat is _squeezed
out_.
Q. _How are the ATOMS of MATTER disturbed by the flame of a candle?_
A. 1st--When the _hydrogen_ of the tallow and _oxygen_ of the air
_condense into water_, a _vacuum_ is made; and the air is disturbed, as
a _pond_ would be, if a pail of _water_ were taken out.
2ndly--When the _carbon_ of tallow and _oxygen_ of the air expand into
_carbonic acid gas_, the air is _again_ disturbed; in a similar way as
by the explosion of _gunpowder_.
Q. _Why does the flame of a CANDLE produce LIGHT?_
A. The chemical changes made by combustion, excite _undulations of
ether_, which (striking the eye) produce light. (see p. 46.)
Q. _Why is the FLAME of a CANDLE YELLOW?_
A. Only the _outer_ coat of the flame is yellow; the _lower_ part of the
flame is _violet_; and the _inside_ of the flame is _hollow_.
Q. _Why is the outside of the flame YELLOW?_
A. Because the _carbon of the tallow_ (being in a state of _perfect
combustion_) is made white-hot.
Q. _Why is the BOTTOM part PURPLE of the flame of a candle?_
A. The _bottom part_ of the flame is _overladen with hydrogen_, raised
from the tallow by the burning wick; and this _half-burnt gas_ gives a
_purple_ tinge to the flame.
Q. _Why is the INSIDE of the flame of a candle HOLLOW?_
A. Because it is _filled with vapour_, raised from the candle by the
_heat of the wick_.
Q. _Describe the different parts of the FLAME of a common CANDLE._
A. The flame consists of _three cones_. The innermost cone is hollow;
the intermediate cone of a dingy purple hue; and the outside cone is
yellow.
Q. _Why is the intermediate cone of a flame PURPLE, as well as the
BOTTOM of the flame._
A. Because the gases are not in a state of _perfect combustion_; but
contain an _excess of hydrogen_, which gives this cone a purple tinge.
Q. _Why is not the MIDDLE cone in a state of perfect combustion, as well
as the OUTER cone?_
A. Because the outer cone _prevents the oxygen of the air_ from getting
freely to the _middle of the cone_; and without the free access of
oxygen gas, there is no such thing as complete combustion.
Q. _Why does the FLAME of a candle point UPWARDS?_
A. The flame _heats the surrounding air_, which (being hot) _rapidly
ascends_, and drives the flame upwards at the same time.
Q. _Why is the FLAME of a candle POINTED at the top, like a cone?_
A. The _upper_ part of a flame is more _volatile_ than the lower parts;
and as it affords _less resistance to the air_, is reduced to a mere
point.
Q. _Why is the UPPER part of a flame more VOLATILE than the lower
parts?_
A. The _lower_ parts of the flame are laden with unconsumed gas and
watery vapour; which present considerable resistance to the air.
Q. _Why is the FLAME of a candle BLOWN OUT by a puff of breath?_
A. As the flame of a candle is attached to a _very small wick_, a puff
of breath _severs the flame from the wick_; and it goes out for want of
support.
Q. _Why does the FLAME of a candle make a GLASS DAMP, which is held over
it?_
A. The _hydrogen of the tallow_ combining with the _oxygen of the air_,
produce a "watery vapour," which is condensed by the _cold glass_ held
above the flame.
Q. _Why does our hand, held ABOVE a candle, suffer from the heat of the
flame so much more, than when it is placed BELOW the flame, or on ONE
SIDE of it?_
A. Because the hot gases and air (in their ascent) _come in contact_
with the hand placed _above_ the flame: but when the hand is placed
_below_ the flame, or on _one side_, it only feels heat from
_radiation_.
Q. _Why is a RUSH LIGHT extinguished so much more quickly than a
cotton-wicked candle?_
A. As the _rush_ wick is _smooth_ and _hard_, the _mere motion of the
air_ (produced by carrying the candle from one place to another,) is
sufficient to sever the flame from the rush.
Q. _Why is it more difficult to blow out a COTTON wick?_
A. The _cotton_ wick is _quite full of small threads_ or filaments,
which help to _hold the flame on the wick_, like the roots of a tree.
Q. _Why does an EXTINGUISHER put a candle out?_
A. Because the air in the extinguisher _is soon exhausted of its oxygen_
by the flame: and when there is no _oxygen to support it_, the flame
goes out.
Q. _Why does not a candle set fire to a PIECE OF PAPER twisted into an
extinguisher, and used as such?_
A. 1st--Because the flame very soon _exhausts the little oxygen_
contained in the paper extinguisher: and
2ndly--The flame invests the _inside of the paper extinguisher_ with
_carbonic acid gas_, which prevents it from blazing.
Q. _Why is a LONG WICK never upright?_
A. Because it is bent by its own weight.
Q. _Why is a LONG WICK covered with an EFFLORESCENCE at the top?_
A. The knotty or flowery appearance of the top of a wick arises _from an
accumulation of particles partly separated_, but still loosely hanging
to the wick.
Q. _Why is not the END of a long wick BURNT OFF, as it hangs over the
flames?_
A. Because the length of the wick so diminishes _the heat of the flame_,
that it is not _hot_ enough to burn it off.
Q. _Why do PALMER'S METALLIC WICKS never need SNUFFING?_
A. The wick is divided into two parts, each of which _bends outward_ to
the outside of the flame; where the _end is intensely heated_, and
_separated_ from the wick by the current of air up the candle.
Q. _Why do common CANDLES require to be SNUFFED?_
A. Because the heat of the flame is _not sufficient to consume the
wick_; and the _longer_ the wick grows, the _less heat_ the flame
produces.
Q. _Why do WAX CANDLES NEVER need SNUFFING?_
A. The wick of _wax_ candles is made _of very fine thread_, which the
heat of the flame is sufficient to consume: but the wick of _tallow_
candles is made _of coarse cotton_, which is too substantial to be
consumed by the heat of the flame, and must be cut off by _snuffers_.
Q. _Why does a PIN, stuck in a RUSH-LIGHT, EXTINGUISH it?_
A. Because a _pin_ (being a good conductor), _carries away the heat of
the flame from the wick_, and prevents the combustion of the tallow.
Q. _What is the SMOKE of a CANDLE?_
A. Solid particles of carbon separated from the wick and tallow, but not
consumed.
Q. _Why are SOME particles consumed and not OTHERS?_
A. The _combustion of the carbon_ depends upon its _combining with the
oxygen of the air_: but as the outer surface of the flame _prevents the
access of air to the interior parts_, therefore much of the carbon of
those parts passes off in smoke.
Q. _Why do LAMPS SMOKE?_
A. Either because the _wick is cut unevenly_, or else because _it is
turned up too high_.
Q. _Why does a LAMP SMOKE when the WICK is cut UNEVENLY?_
A. 1st--Because the _points of the jagged edge_ (being very easily
separated from the wick,) _load the flame with more carbon than it can
consume_: and
2ndly--As the heat of the flame is _greatly diminished by these bits of
wick_, it is unable to consume _even the usual quantity of smoke_.
Q. _Why does a LAMP SMOKE when the WICK is turned up too HIGH?_
A. Because more carbon is separated from the wick _than can be consumed
by the flame_.
Q. _Why do not "Argand burners" smoke?_
A. Because a current of air passes through the _middle of the flame_;
and therefore the carbon of the _interior_ is consumed, as well as that
_in the outer coating of the flame_.
Q. _Why does a LAMP-GLASS DIMINISH the SMOKE of a lamp?_
A. Because it both _concentrates and reflects the heat of the flame_; in
consequence of which, the heat is so greatly increased, _that very
little carbon escapes unconsumed_.