Q. _What is c.o.kE?_

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 c.o.ke, 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 ma.s.ses_ 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 ma.s.s 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 Ma.s.s of goods GREATER than that of a smaller quant.i.ty?_

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.)

CHAPTER IV.

SMOKE.

Q. _Why does SMOKE ASCEND the chimney?_

A. As the air of the room pa.s.ses over the fire, it becomes _heated_; and (being thus made _lighter_,) ascends the chimney, carrying the smoke with it.

Q. _What is SMOKE?_

A. Small particles of carbon, separated by combustion from the fuel, but not _consumed_.

Q. _Why do SMOKE and steam CURL, as they ascend?_

A. Because they are moved in a _right line_, and then _pushed on all sides_; and this forces them into a _circular_ motion.

Q. _What are BLACKS?_

A. When the hot air of the chimney has been cooled by the _external_ air, it can no longer _buoy up_ the solid smoke; so it falls to the earth in condensed flakes, called "blacks."

Q. _Why are there NO BLACKS in the smoke of a RAILWAY engine?_

A. The smoke of a railway engine consists chiefly of _watery vapour_, which dissolves in air, as sugar does in water; but the smoke of a common chimney consists of small fragments of _unburnt fuel_.

Q. _Why does a "COPPER HOLE" DRAW up more fiercely than an OPEN stove?_

A. As the air, which supplies the copper hole, must pa.s.s _through the furnace_, it becomes exceedingly _heated_, and rushes up the chimney with great violence.