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?_