A Guide To The Scientific Knowledge Of Things Familiar Part 24

A. Yes, much more. There is as much condensed air in a common apple, as would fill a s.p.a.ce 48 _times as big as the apple itself_.

Q. _Where is all this quant.i.ty of AIR stowed in the APPLE?_

A. The _inside_ of an apple is _made up of little cells_ (like a _honey-comb_), each of which contains a portion of the air.

Q. _When an APPLE is ROASTED, why is one part made SOFT, while all the rest remains hard?_

A. When an apple is roasted, the air in the _cells next to the fire_ is expanded and flies out; the _cells are broken_, and their juices _mixed together_; so the apple _collapses_ (from loss of air and juice), and feels _soft_ in those parts.

Q. _What is meant by the "apple COLLAPSING?"_

A. The _plumpness_ gives way, and the apple becomes _flabby_ and _shrivelled_.

Q. _Why do SPARKS of fire start (with a crackling noise) from pieces of WOOD laid upon a FIRE?_

A. The _air_ in the wood (expanded by the heat), _forces its way through the pores of the log_; and carries along with it the _covering of the pore_, which resisted its pa.s.sage.

Q. _What is meant by the "PORES of the WOOD?"_

A. Very small _holes in the wood_, through which the _sap_ circulates.

Q. _What are the SPARKS OF FIRE, which burst from the WOOD?_

A. Very small pieces of wood _red hot_, separated from the log by the _force of the air_, as it bursts from its confinement.

Q. _Why does DEAL make more snapping than any OTHER WOOD?_

A. The pores of deal are _very large_, and contain much _more air_ than wood of a _closer grain_.

Q. _Why does DRY WOOD make more SNAPPING than GREEN WOOD?_

A. In _green wood_ the pores are filled with _sap_, and therefore contain _very little air_; but in _dry_ wood the sap is _dried up_, and the pores are filled with _air_ instead.

Q. _Why does DRY wood BURN more easily than GREEN or wet wood?_

A. Because the pores of dry wood are _filled with air_, which supports combustion; but the pores of green or wet wood are filled with _vapour_, which extinguishes flame.

Q. _Why does VAPOUR EXTINGUISH FLAME?_

1st--Because the coat of water (which wraps the fuel round) prevents the _oxygen_ of the air from getting to the _fuel_, to form into _carbonic acid gas_: and

2ndly--Heat is perpetually carried off, by the formation of the sap or water _into steam_.

(Carbonic acid gas is a compound of carbon and oxygen. The solid part of the fuel is _carbon_, and one of the gases of the air is oxygen.)

Q. _What has CARBONIC ACID GAS to do with COMBUSTION?_

A. Combustion is produced by the _chemical action_ which takes place, while the _carbon_ of fuel unites with the _oxygen_ of air, and forms "_carbonic acid gas_." (See p. 36.)

Q. _Why do STONES SNAP and fly about, when heated in the FIRE?_

A. The air in the stones (expanded by the heat of the fire), _meets with great resistance_ from the close texture of the stone; and, therefore, _bursts forth with great violence_, tearing the stone to atoms, and forcing the fragments into the room.

Q. _Must not AIR be very STRONG, to shatter into atoms a hard stone?_

A. Yes. All the dreadful effects of _gunpowder_ are merely the results of the _sudden expansion of air_.

Q. _When bottled ALE and PORTER is set before a FIRE, why is the CORK FORCED OUT sometimes?_

A. If the bottle be _not quite full_, there will be _air_ between the liquor and the cork; this _air_ (expanded by the heat of the fire) _forces out the cork_.

Q. _Why does ALE or PORTER FROTH more, after it has been set before the fire?_

A. The _froth_ of ale or porter _depends upon the pressure_ to which it is subjected; and as the air (between the liquor and the cork) is _expanded_ by the heat, _it presses against the liquor_, and increases the quant.i.ty of froth.

Q. _Why is the FROTH of ale and porter INCREASED by PRESSURE?_

A. Because the liquor absorbs _carbonic acid_ so long as it is under _pressure_; and the moment that the pressure is _removed_, the carbonic acid _escapes_ in foam or froth.

Q. _When a boy makes a BALLOON, and sets fire to the cotton or sponge (which has been steeped in spirits of wine), why is the balloon INFLATED, or blown out?_

A. The _air_ inside the balloon is _expanded by the flame_, till the whole balloon is _blown out_ without a crumple.

Q. _Why does the BALLOON RISE, after it has been inflated by the expanded air?_

A. The same quant.i.ty of air is expanded _to three or four times its original volume_; and is made so much _lighter than common air_, that even when all the paper, wire, and cotton are added, it is still lighter bulk for bulk.

Q. _What is meant by being lighter "bulk for bulk?"_