A Guide To The Scientific Knowledge Of Things Familiar Part 12

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 pa.s.ses 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 pa.s.ses 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, _rus.h.i.+ng 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 quant.i.ty 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.