Q. _What is the third chief source of heat?_
A. CHEMICAL ACTION.
Q. _What is meant by chemical action being the source of heat?_
A. Many things, when their chemical constitution is changed, (either by
the abstraction of some of their gases, or by the combination of others
not before united,) evolve _heat_, while the change is going on.
Q. _Explain by illustration what you mean._
A. Water is cold, and sulphuric acid is cold; but if these two _cold_
liquids be mixed together, they will produce _boiling heat_.
Q. _Why will COLD WATER, mixed with SULPHURIC ACID, produce heat?_
A. Because water (being _lighter_ than sulphuric acid), is _condensed_
by the heavier liquid; and its heat is _squeezed out_, as water from a
sponge.
Q. _Why does COLD WATER, poured on LIME, make it intensely HOT?_
A. The heat is evolved by the chemical action, produced by the cold
water combining with the lime.
Q. _Where does the heat come from?_
A. It was in the water and lime before; but was in a _latent state_.
Q. _Was there heat in the cold water and lime, before they were mixed
together?_
A. Yes. _All_ bodies contain heat; the coldest ice, as well as the
hottest fire.
Q. _Is there HEAT even in ICE?_
A. Yes. But it is _latent_, (i. e. not perceptible to our senses).[4]
[4] Latent, from the Latin word, Lateo, (to lie hid.)
Q. _How do you know there is heat, if you cannot perceive it?_
A. Thus:--Ice is 32° by the thermometer; but if ice be _melted_ over a
fire, (though 140° of heat are thus absorbed,) it will feel no _hotter_
than it was before. (_i. e. it will be only 32°, and not 172°_)[5].
[5] 32°, i. e. 32 degrees; 140°, i. e. 140 degrees, &c.
Q. _What becomes of the 140°, which went into the ice to melt it?_
A. It is hidden in the water; or (to speak more scientifically) it is
stored up in a _latent state_.
Q. _How much heat may be thus secreted or made latent?_
A. _All_ things contain a vast quantity of latent heat; but, as much as
1140° of heat may remain latent in _water_.
Q. _How can 1140° of heat be added to water, without being perceptible
to our feelings?_
A. 1st--140° of heat are hidden in the water, when ice is melted by the
sun or fire.
2ndly--1000° more of heat are secreted, when water is converted into
steam. Thus, before ice is converted into steam, 1140° of heat become
_latent_.[6]
[6] Thus, one pint of boiling water, (212° according to the
thermometer,) will make 1800 pints of steam; but the steam is no hotter
to the touch than boiling water, both are 212°: therefore, when water is
converted into steam, 1000° of heat become latent. Hence, before ice is
converted to steam, it must contain 1140° of latent heat.
Q. _Can we be made to FEEL the heat of ICE or snow?_
A. Yes. Into a pint of snow put half as much salt; then plunge your hand
into the liquid; and it will feel so intensely cold, that the snow
itself will seem quite _warm_ in comparison to it.
Q. _Is SALT and SNOW really COLDER than snow?_
A. Yes, many degrees; and by dipping your hand into the mixture
_first_, and into snow _afterwards_, the mere snow will seem to be
comparatively warm.
Q. _What is FIRE?_
A. Combustion is another instance of heat, arising from chemical action.
Q. _What two things are essential to produce combustion?_
A. Fuel and air.
Q. _What are the elements of fuel?_
A. As bread is a compound of flour, yeast, and salt; so fuel is a
compound of hydrogen and carbon.
Q. _What are the ELEMENTS of atmospheric AIR?_
A. The air is a compound of oxygen and nitrogen _mixed_ together; in the
proportion of five gallons of nitrogen, to one of oxygen.
Q. _What is CARBON?_
A. The solid part of fuel. It abounds also in all animal bodies, earths,
and minerals.
Q. _Mention some different SPECIES of CARBON._
A. Common charcoal, lamp-black, coke, black lead, and the diamond, are
all varieties of carbon.
Q. _What is HYDROGEN?_
A. An inflammable gas. The gas used in our streets, is only the hydrogen
gas _driven out of coals by heat_.
Q. _What are the peculiar characteristics of hydrogen gas?_
A. Though this gas _itself_ will _burn_, yet a candle will _not_ burn
when immersed in it; nor can an animal live in it. Hydrogen gas is the
lightest of all known substances.[7]
[7] Hydrogen gas may be made thus:--Put some pieces of zinc or iron
filings into a glass: pour over them a little sulphuric acid (vitriol),
diluted with twice the quantity of water; then cover the glass over for
a few minutes, and hydrogen gas will be given off.
EXP. If a flame be put into the glass, an EXPLOSION will be made.
If the experiment be tried in a phial, which has a piece of tobacco-pipe
run through the cork; and a light held a few moments to the top of the
pipe, a FLAME will be made.
If a balloon be held over the phial, (so that the gas can inflate it,)
the balloon will ascend in a very few minutes.
Q. _What is OXYGEN?_
A. A gas, much heavier than hydrogen; which gives brilliancy to flame,
and is essential to animal life.[8]
[8] Oxygen gas is much more troublesome to make than hydrogen. The
_cheapest_ plan is to put a few ounces of manganese (called the black
oxide of manganese) into an iron bottle, furnished with a bent tube;
set the bottle on a fire till it becomes red hot, and put the end of the
tube into a pan of water. In a few minutes, bubbles will rise through
the water; these bubbles are oxygen gas.
These bubbles may be collected thus:--Fill a common bottle with water;
hold it topsy-turvy over the bubbles which rise through the pan, but be
sure the mouth of the bottle be held _in the water_. As the bubbles rise
into the bottle, the water will run out; and when all the water has run
out, the bottle is full of gas. Cork the bottle while the _mouth remains
under water_; set the bottle on its base; cover the cork with lard or
wax, and the gas will keep till it be wanted.
N. B. The _quickest_ way of making oxygen gas, is to rub together in a
mortar half an ounce of oxide of copper, and half an ounce of chlorate
of potassa. Put the mixture into a common oil flask, furnished with a
cork which has a bent tube thrust through it. Heat the bottom of the
flask over a candle or lamp; and when the mixture is red hot, oxygen gas
will be given off. Note--the tube must be immersed in a pan of water,
and the gas collected as before.
(Chlorate of potassa may be bought at any chemist's; and oxide of copper
may be procured by heating a sheet of copper red hot, and when cool,
striking it with a hammer: the scales that peel off, are oxide of
copper.)
EXP. Put a piece of red hot charcoal, (fixed to a bit of wire,) into
your bottle of oxygen gas; and it will throw out most dazzling sparks of
light.
Blow a candle out; and while the wick is still red, hold the candle (by
a piece of wire,) in the bottle of oxygen gas; the wick will instantly
ignite, and burn brilliantly.
(Burning sulphur emits a _blue_ flame, when immersed in oxygen gas.)
Q. _What is NITROGEN?_
A. Nitrogen is another invisible gas. It _will not_ burn, like hydrogen;
and an animal cannot live in it: it abounds in animal and vegetable
substances, and is the chief ingredient of the common air.[9]
[9] Nitrogen gas may easily be obtained thus:--Put a piece of burning
phosphorus on a little stand, in a plate of water; and cover a bell
glass over. (Be sure the edge of the glass stands _in the water_.) In a
few minutes the air will be decomposed, and nitrogen alone remain in the
bell glass.
(N.B. The white fume which will arise and be absorbed by the water in
this experiment, is phosphoric acid; i. e. phosphorus combined with
oxygen of the air.)
Q. _Why is there so much nitrogen in the air?_
A. In order to _dilute_ the oxygen. If the oxygen were not thus diluted,
fires would burn out, and life would be exhausted too quickly.
Q. _What three elements are necessary to produce COMBUSTION?_
A. Hydrogen gas, carbon, and oxygen gas; the two former in the _fuel_,
and the last in the _air_ which surrounds the fuel.
Q. _What causes the combustion of the fuel?_
A. The hydrogen gas of the fuel being set free, and excited by a piece
of lighted paper, instantly _unites_ with the _oxygen of the air_, and
makes a yellow flame: this flame heats the _carbon of the fuel_,
which also unites with the oxygen of the air, and produces _carbonic
acid gas_.
Q. _What is carbonic acid gas?_
A. Only carbon (or charcoal) combined with oxygen gas.
Q. _Why does FIRE produce HEAT?_
A. 1st--By liberating _latent heat_ from the air and fuel: and
2ndly--By throwing into _rapid motion_ the _atoms of matter_.
Q. _How is latent HEAT liberated by COMBUSTION?_
A. When the _oxygen_ of the air combines with the _hydrogen_ of the
fuel, the two gases _condense into water_; and latent heat is _squeezed
out_, as water from a sponge.
Q. _How are the ATOMS OF MATTER DISTURBED by COMBUSTION?_
A. 1st--When _hydrogen_ of fuel and _oxygen_ of 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 of it: and
2ndly--When the _carbon_ of fuel and _oxygen_ of air _expand into
carbonic acid gas_, the air is _again_ disturbed, as it would be by
the explosion of _gunpowder_.
Q. _How does fire condense HYDROGEN and OXYGEN into WATER?_
A. The _hydrogen of fuel_ and _oxygen of air_ (liberated by combustion)
combining together, _condense into water_.
Q. _How does fire expand CARBON into CARBONIC ACID GAS?_
A. The _carbon of fuel_ and _oxygen of air_ (combining together in
combustion) expand into a gas, called _carbonic acid_.
Q. _Why is a FIRE (after it has been long burning) RED HOT?_
A. When coals are heated _throughout_, the carbon is so completely mixed
with the oxygen of the air, that the _whole surface is in a state of
combustion_, and therefore _red hot_.
Q. _In a BLAZING fire, why is the UPPER surface of the COALS BLACK, and
the LOWER surface RED?_
A. Carbon (being very solid) requires a great degree of heat to make it
unite with the oxygen of the air. When fresh coals are put on, their
_under_ surface is heated before the upper surface; and one is _red_ (or
in a state of combustion), while the other is _black_.
Q. _Which burns the quicker, a BLAZING fire, or a RED HOT one?_
A. A _blazing_ fire burns out the fuel quickest.
Q. _Why do BLAZING COALS BURN QUICKER than red hot ones?_
A. In red hot coals, only the _mere surface_ is in a state of
combustion, because the carbon is _solid_; but in a _blazing_ fire,
(where the gases are escaping), the _whole volume of the coal
throughout_ is in a state of decomposition.
Q. _What is SMOKE?_
A. _Unconsumed_ parts of fuel (principally carbon), separated from the
solid mass, and carried up the chimney by the current of hot air.
Q. _Why is there MORE SMOKE when COALS are FRESH added, than when they
are red hot?_
A. Carbon (being solid), requires a great degree of heat to make it
unite with oxygen, (or, in other words, to bring it into a state of
perfect combustion): when coals are fresh laid on, _more carbon is
separated_ than can be _reduced to combustion_; and so it flies off in
smoke.
Q. _Why is there so LITTLE SMOKE with a RED HOT FIRE?_
A. When a fire is red hot, the _entire surface_ of the coals is in a
_state of combustion_; so a very little flies off unconsumed, as smoke.
Q. _Why are there DARK and BRIGHT SPOTS in a CLEAR cinder FIRE?_
A. Because the _intensity_ of the combustion is _greater in some parts_
of the fire, than it is in _others_.
Q. _Why is the intensity of the combustion so unequal?_
A. Because the air flies to the fire in various and unequal currents.
Q. _Why do we see all sorts of GROTESQUE FIGURES in hot COALS?_
A. Because the _intensity_ of combustion is so _unequal_, (owing to the
gusty manner in which the air flies to the fuel; and the various shades
of red, yellow, and white heat mingling with the black of the unburnt
coal), produce strange and fanciful resemblances.
Q. _Why does PAPER BURN more readily than wood?_
A. Merely because it is of a _more fragile texture_; and, therefore, its
component parts are more easily heated.
Q. _Why does WOOD BURN more readily than coal?_
A. Because it is not so _solid_; and, therefore, its elemental parts are
more easily separated, and made hot.
Q. _When a FIRE is LIGHTED, why is PAPER laid at the BOTTOM, against the
grate?_
A. Because paper (in consequence of its fragile texture), so very
readily catches fire.
Q. _Why is WOOD laid on the top of the paper?_
A. Because wood, (being more _substantial_), _burns longer_ than
paper; and, therefore, affords a _longer contact of flame_ to heat the
coals.
Q. _Why would not paper do without wood?_
A. Because paper burns out so _rapidly_, that it would not afford
sufficient _contact of flame_ to heat the coals to combustion.
Q. _Why would not WOOD do WITHOUT shavings, straw, or paper?_
A. Because wood is too _substantial_ to be heated into combustion, by
the flame issuing from a mere _match_.
Q. _Why would not the paper do as well, if placed on the TOP of the
coals?_
A. As every blaze _tends upwards_, if the paper were placed on the _top_
of the fire, its blaze would afford _no contact of flame_ to fuel lying
_below_.
Q. _Why should COAL be placed ABOVE the wood?_
A. As every flame tends _upwards_, if the wood were _above the coal_,
the _flame_ would not rise _through the coal_ to heat it.
Q. _Why is a FIRE KINDLED at the LOWEST BAR of a grate?_
A. As every flame tends _upwards_; when a flame is made at the _bottom_
of a fire, it _ascends through the fuel_ and heats it: whereas, if the
fire were lighted from the _top_, the flame would _not come into
contact_ with the fuel piled below.
Q. _Why does COAL make such EXCELLENT FUEL?_
A. Because it is so very _hard_ and _compact_, that it burns away very
slowly.
Q. _Why will CINDERS become RED HOT, quicker than COALS?_
A. Because they are _more porous_ and _less solid_; and are, therefore,
sooner reduced to a state of combustion.
Q. _Why will not IRON CINDERS burn?_
A. Iron cinders are _cinders saturated with oxygen_; they are unfit for
fuel, because they can imbibe _no more oxygen_, being saturated already.
Q. _Why are CINDERS lighter than COALS?_
A. Because their vapour, gases, and volatile parts, have been driven off
by _previous combustion_.
Q. _Why will not STONES do for fuel, as well as COALS?_
A. Because they contain no _hydrogen_ (or inflammable gas) like coals.
Q. _Why will not WET KINDLING light a fire?_
A. 1st--Because the moisture of the wet kindling prevents the _oxygen of
the air from getting to the fuel_ to form it into carbonic acid gas:
and
2ndly--The heat of the fire is perpetually _drawn off_, by the
conversion of _water_ into _steam_.
Q. _Why does DRY wood burn BETTER than GREEN?_
A. 1st--Because no heat is _carried away_, by the conversion of _water
into steam_: and
2ndly--The pores of dry wood _are filled with air_, which supply the
fire with oxygen.
Q. _Why do TWO pieces of WOOD burn BETTER than ONE?_
A. 1st--Because they help to entangle the _heat of the passing smoke_,
and _throw it on the fuel_: and
2ndly--They help to _entangle the air_ that passes over the fire, and
create a kind of _eddy_ or draught.
Q. _Why does SALT CRACKLE when thrown into a FIRE?_
A. Salt contains _water_; and the _cracking_ of the salt is owing to the
sudden _conversion of the water into steam_.
Q. _Why will not wood or paper burn, if they are steeped in a solution
of POTASH, phosphate of LIME, or AMMONIA (hartshorn)?_
A. Because any "al'kali" (such as potash) will _arrest the hydrogen_ (as
it escapes from the fuel), and prevent its _combination_ with the
_oxygen of air_.
Q. _What is an al'kali?_
A. The con'verse of an _acid_; as _bitter_ is the con'verse of _sweet_,
or _insipid_ the con'verse of _pungent_.
Q. _Why does a JET of FLAME sometimes burst into the room THROUGH THE
BARS OF A STOVE?_
A. The iron bars conduct heat to the _interior of some lump of coal:_
and its volatile gas (bursting through the weakest part) is kindled by
the glowing coals over which it passes.
Q. _Why is this JET sometimes of a GREENISH YELLOW colour?_
A. When a lump of coals lies _over the hot bars_, or the coals below it
are not _red hot_, the gas which bursts from the lump _escapes unburnt_,
and is of a greenish colour.
Q. _Why does the gas escape UNBURNT?_
A. Because neither the _bars_ nor _coals_ (over which it passes) are
_red-hot_.
Q. _Why does a BLUISH FLAME sometimes flicker on the surface of hot
cinders?_
A. Gas from the hot coals _at the bottom of the grate_ mixing with the
_carbon of the coals above_, produces an inflammable gas (called
carbonic oxide), which burns with a blue flame.
Q. _Why is the FLAME of a good fire YELLOW?_
A. Because both the hydrogen and carbon of the fuel are in a state of
_perfect combustion_. It is the _white heat of the carbon_, which gives
the pale yellow tinge to the flaming hydrogen.
Q. _What is LIGHT?_
A. Rapid _undulations_ of a fluid called _ether_, striking on the eye.
Q. _How does COMBUSTION make these undulations of LIGHT?_
A. The atoms of matter (set in motion by heat) _striking against_ this
ether, produce _undulations_ in it; as a _stone_ thrown into a stream,
would produce undulations in the _water_.
Q. _How can UNDULATIONS of ether produce LIGHT?_
A. As _sound_ is produced by _undulations of air_ striking on the
_ear_; so _light_ is produced by undulations of _ether_ striking on the
_eye_.
Q. _What is ETHER?_
A. A very subtile fluid, which pervades and surrounds _every thing we
see_.
Q. _Mention a simple experiment to prove that LIGHT is produced by rapid
MOTION._
A. When a fiddle-string is _jerked_ suddenly, its rapid vibration
produces a grey _light_; and when a carriage wheel revolves very
quickly, it sends forth a similar light.
Q. _Does HEAT ALWAYS produce LIGHT?_
A. No: the heat of a stack of hay, or reeking dunghill, though very
_great_, is not sufficient to produce _light_.
Q. _Why is a YELLOW FLAME brighter than a RED HOT COAL?_
A. Because _yellow rays_ always produce the greatest amount of _light_;
though _red rays_ produce the greatest amount of _heat_.
Q. _Why is the LIGHT of a fire MORE INTENSE sometimes than at others?_
A. The _intensity_ of fire-light depends upon the _whiteness_ to which
the carbon is reduced, by combustion. If the carbon be _white hot_, its
_combustion is perfect_, and the light intense; if not, the light is
obscured by _smoke_.
Q. _Why will not CINDERS BLAZE, as well as FRESH coals?_
A. The _flame_ of coals is made chiefly by _hydrogen gas_. As soon as
this gas is consumed, the hot cinders produce only an _invisible_ gas,
called carbonic acid.
Q. _Where does the hydrogen gas of a fire come from?_
A. The _fuel is decomposed_ (by combustion) into its simple elements,
carbon and hydrogen gas. (see p. 33)
Q. _Why does not a FIRE BLAZE on a FROSTY NIGHT, so long as it does upon
another night?_
A. The air (being very cold) _rushes to the fire so rapidly_, that the
coals burn out _faster_, and the inflammable gas _is sooner consumed_.
Q. _Why does a FIRE burn CLEAREST on a FROSTY night?_
A. Because the volatile gases are quickly consumed; and the solid
carbon _plentifully supplied with air_, to make it burn bright and
intensely.
Q. _Why does a FIRE burn more intensely in WINTER than in SUMMER time?_
A. Because the air is _colder_ in winter, than in summer-time.
Q. _How does the COLDNESS of the air increase the HEAT of a fire?_
A. For two reasons: 1st--Because cold air being more _condensed_ than
hot air, contains a greater _body_: and
2ndly--Cold air _rushes more quickly to the fire_, and supplies more
_oxygen_.
Q. _Why does the SUN, shining on a FIRE, make it DULL, and often put it
out?_
A. 1st--When the sun shines, the air is rarefied; and, therefore, _flows
more slowly to the fire_.
2ndly--As the air is _rarefied_, even that which _reaches_ the fire,
_affords less nourishment_.
Q. _Why does the air flow to the fire more TARDILY for being RAREFIED?_
A. The greater the _contrast_ (between the _external air_, and that
_which has been heated by the fire_) the more _rapid_ will be the
current of air towards that fire.
Q. _Why does rarefied air afford LESS NOURISHMENT to fire, than cold
air?_
A. Because it is _spread out_, (like a piece of gold _beaten into
leaf_); and as a square inch of gold _leaf_ will not contain so much
gold as a square inch of _bullion_--so, a square inch of _rarefied_ air
has less _body_, than a square inch of _cold air_.
Q. _Why does a FIRE burn more fiercely in the OPEN AIR?_
A. 1st--Because the _air out-of-doors_ is more _dense_, than the air
in-doors: and
2ndly--Because air is _more freely supplied_ to a fire out-of-doors.
Q. _Why is the air out-of-doors more DENSE than that in-doors?_
A. Because the circulation is more free; and as soon as any portion has
been _rarefied_, it instantly escapes, and is supplied by _colder
currents_.
Q. _Why does not a FIRE burn so freely in a THAW, as in a FROST?_
A. During a thaw, the air is filled with _vapour_; and, both _moves too
slowly_, and is _too much diluted_ to nourish the fire.
Q. _Why does a FIRE burn so fiercely in WINDY weather?_
A. In windy weather the _air is rapidly changed_, and affords plentiful
nourishment to the fire.
Q. _Why do a pair of BELLOWS get a fire up?_
A. A pair of bellows, (like the wind), _drives the air more rapidly to
the fire_; and the plentiful supply of oxygen soon makes the fire burn
intensely.
Q. _Why is a CANDLE BLOWN OUT by the breath, and not made more intense,
like a fire?_
A. As the flame of a candle is confined to a _very small wick_, it is
_severed_ from it by the breath; and (being unsupported) _must go out_.
Q. _Why is a SMOULDERING WICK sometimes REKINDLED by blowing it?_
A. The breath carries the air to it with _great rapidity_; and the
oxygen of the air kindles the _red hot wick_, as it kindles charred
wood.
Q. _Why is not the red hot wick kindled by the air AROUND it, without
BLOWING it?_
A. Because oxygen is not supplied with sufficient freedom, unless it be
_blown_ to the wick.
Q. _When is this experiment most likely to succeed?_
A. In _frosty_ weather; because the air contains more oxygen then,
_being condensed by the cold_.
Q. _Why does a POKER, LAID ACROSS a dull FIRE, revive it?_
A. For two reasons. 1st--Because the poker _concentrates the heat_, and
therefore increases it: and
2ndly--Because the poker _arrests the air_ which passes over the fire,
and _produces a draught_.
Q. _Why do SEVERAL PIECES of WOOD or coal burn BETTER than ONE?_
A. When there are two or three pieces of wood on a fire, the air
_(circulating round them) produces an eddy_ or draught, which draws up
the fire.
Q. _Why are STOVES fixed on the FLOOR of a room?_
A. In order that the air, _on the lower part of the room_, may be heated
by the fire.
Q. _Would not the air of the lower part of a room be heated equally
well, if the stoves were fixed higher up?_
A. No; the heat of a fire has a very little effect upon the air _below
the level of the grate_; and, therefore, every grate should be as _near
to the floor_ as possible.
Q. _Why are our FEET so COLD when we sit close by a good fire?_
A. As the fire consumes the air which passes over it, _cold air_ rushes
through the crevices of the doors and windows _along the bottom of the
room_ to supply the deficiency; and these currents of cold air, _rushing
constantly over our feet_, deprive them of their warmth.
Q. _If a piece of PAPER be laid FLAT on a clear fire, it will NOT BLAZE,
but CHAR. Why so?_
A. The carbon of a clear fire, being sufficiently hot to unite with the
oxygen of the air, _produces carbonic acid gas_, which soon envelops
the paper laid flat upon the cinders: but carbonic acid gas will not
_blaze_.
Q. _If you BLOW the paper, it will BLAZE immediately. Why so?_
A. By blowing, or opening the door suddenly, _the carbonic acid is
dissipated_, and the paper is instantly fanned into flame.
Q. _Why does WATER EXTINGUISH a FIRE?_
1st--Because the water _forms a coating_ over the fuel, and keeps it
from the air:
2ndly--The conversion of _water into steam_, draws off the _heat_ of the
burning fuel.
Q. _Why does a LITTLE WATER make a fire FIERCER, while a LARGER quantity
of water puts it OUT?_
A. Water is composed of _oxygen and hydrogen_; when, therefore, the fire
can decompose the water into its simple elements, it serves for _fuel_
to the flame.
Q. _How can WATER serve for FUEL to fire?_
A. The _hydrogen_ of the water will burn with a _flame_; and the
_oxygen_ of the water will increase the _intensity_ of that flame.
Q. _If a house be on fire, is too LITTLE water worse than NO water at
all?_
A. Certainly. Unless the water be supplied so plentifully as _to quench
the fire_, it will increase the _intensity_, like fuel.
Q. _When will water EXTINGUISH FIRE?_
A. When the supply is so rapid and abundant, that the fire cannot
_convert it into steam_.
Q. _Does not a very LITTLE water SLACKEN the heat of fire?_
A. Yes, _till it is converted into steam_; but then it increases the
_intensity_ of fire, and acts like fuel.
Q. _Why does the WICK of a candle (when the flame has been blown out)
CATCH FIRE so readily?_
A. As the wick is already _very hot_, a little _extra_ heat will throw
it into flame.
Q. _Why does the EXTRA heat revive the flame?_
A. Because it again liberates the _hydrogen_ of the tallow, and ignites
it.
Q. _Cannot WOOD be made to BLAZE without actual contact with fire?_
A. Yes; if a piece of wood be held _near_ the fire for a little time it
will blaze, even though it does not _touch_ the fire.
Q. _Why will WOOD BLAZE, even if it does not touch the fire?_
A. The heat of the fire _drives out the hydrogen gas_ of the wood; which
is inflamed by contact with the red-hot coals.
Q. _Why will a NEIGHBOUR'S HOUSE sometimes CATCH FIRE, though no flame
of the burning house ever touches it?_
A. The heat of the burning house sets at liberty _the hydrogen gas_ of
the neighbouring wood-work, which is ignited by the flames or red-hot
bricks of the house on fire.
Q. _What is COKE?_
A. Coal freed from its volatile gases, by the action of artificial heat.
Q. _Why do ARNOTT'S STOVES sometimes SMELL so strong of SULPHUR?_
A. The fire is made of coke, which contains sulphur; and, whenever the
draught is not rapid enough _to drive the sulphur up the flue_, it is
emitted into the room.
Q. _What is meant by SPONTANEOUS COMBUSTION?_
A. Ignition produced by the action of _one uninflamed_ body on another.
Q. _Give an example of spontaneous combustion._
A. Goods packed in a warehouse will often catch fire of _themselves_;
especially such goods as cotton, flax, hemp, rags, &c.
Q. _Why do such GOODS sometimes CATCH FIRE of themselves?_
A. Because they are piled together in very _great masses_ in a _damp_
state or place.
Q. _Why does this produce spontaneous combustion?_
A. The damp produces _decay_ or the decomposition of the goods, and the
great heat of the piled-up mass makes the decaying goods _ferment_.
Q. _How does this FERMENTATION produce COMBUSTION?_
A. During fermentation, _carbonic acid gas_ is given off by the
goods,--a slow combustion ensues,--till at length the _whole pile_
bursts into _flame_.
Q. _Why is the HEAT of a LARGE MASS of goods GREATER than that of a
smaller quantity?_
A. Because compression _squeezes out_ heat, as water is squeezed from a
sponge; and as the goods of a large pile are greatly _compressed_, much
of their latent heat is _squeezed out_.
Q. _Why do HAY-STACKS sometimes CATCH FIRE of themselves?_
A. Either because the hay was got up _damp_, or because rain has
penetrated the stack.
Q. _Why will a HAY-STACK CATCH FIRE if the hay be damp?_
A. Damp hay soon _decays_, and undergoes a _state of fermentation_;
during which, _carbonic acid gas_ is given off, and the stack catches
_fire_.
Q. _Why does roasted COFFEE sometimes CATCH FIRE spontaneously?_
A. The _heat_ of coffee is greatly increased by being _roasted_; and the
_carbon of the coffee_ uniting with the _oxygen of the air_, produces
_carbonic acid gas_, and bursts into _flame_.
Q. _Why do old RAGS, used for CLEANING LAMPS and CANDLES, sometimes set
a HOUSE on FIRE?_
A. Because they very readily _ferment_, and (during fermentation) throw
off exceedingly inflammable gases.
(N.B. Lamp-black mixed with linseed oil is more liable to spontaneous
combustion, than anything that servants handle.)