A Guide To The Scientific Knowledge Of Things Familiar Part 16

Q. _If the opening of a chimney be TOO LARGE, what REMEDY can be applied?_

A. The chimney-place must be contracted.

Q. _Why will CONTRACTING the chimney-place PREVENT its SMOKING?_

A. As the air will then pa.s.s _nearer the fire_, it will be _more heated_, and fly up the chimney _much faster_.

Q. _Why do almost all CHIMNEYS SMOKE in GUSTY weather?_

A. The gust (blowing the air _away_ from the top of the chimney) _removes_ (for a time) _all resistance to the smoke_: but when the wind _lulls_ again, the _resistance of the air suddenly returns_--the _draught_ is _checked_--and a puff of smoke rushes into the room.

Q. _What is the use of a CHIMNEY-POT?_

A. When the opening of a chimney is _large_, the top must be contracted by a chimney-pot, in order to increase the draught.

Q. _How does a CHIMNEY-POT INCREASE the DRAUGHT of a chimney?_

A. As the _same quant.i.ty_ of hot air has to escape _through a much smaller opening_, it must pa.s.s through more quickly.

Q. _Why do tin BLOWERS help to get a fire up?_

A. Because they compel the air to go _through_ the fire, and not _over_ it; therefore the fire is well supplied with oxygen, and the draught greatly increased.

Q. _Why does a tin BLOWER INCREASE the DRAUGHT?_

A. As all the air which enters the chimney has to pa.s.s _through_ the fire, it is much hotter, and ascends the chimney very fast; and the faster the air _flies up the chimney_, the faster it rushes _towards the fire_ also.

Q. _Why does a parlour often SMELL disagreeably of SOOT in SUMMER-TIME?_

A. The air in the _chimney_ (being _colder_ than the air in the _parlour_) _descends into the room_, and leaves a disagreeable smell of soot behind.

Q. _Why are the CEILINGS of PUBLIC OFFICES so BLACK and filthy?_

A. The heated air ascending, carries the dust and fine soot to the ceiling; where the hot _air_ escapes through the plaster, and _leaves the soot and dust_ behind.

Q. _Why are SOME parts of the ceiling BLACKER and more filthy than others?_

A. As the air cannot penetrate the thick _joists_ of the ceiling, _it pa.s.ses by those parts_, and deposits its soot and dust on those which are more penetrable.

Q. _What is CHARCOAL?_

A. Wood which has been exposed to a red heat, till it has been deprived of all its gases and volatile parts.

Q. _Why is a CHARCOAL FIRE hotter than a wood fire?_

A. Because so large a quant.i.ty of _water_ has been abstracted from the fuel, by the red heat to which it has been already exposed.

Q. _Why does charcoal REMOVE the TAINT of meat?_

A. Because it absorbs all odoriferous effluvia, whether they arise from putrefying animal or vegetable matter.

Q. _Why is WATER PURIFIED by being filtered through charcoal?_

A. Charcoal absorbs the _impurities_ of the water, and removes all disagreeable tastes and smells, whether they arise from animal or vegetable matter.

Q. _Why are water and wine CASKS CHARRED inside?_

A. _Charring_ the inside of the cask reduces it to a _kind of charcoal_; and charcoal (by absorbing animal and vegetable impurities) keeps the liquor sweet and good.

Q. _Why does a piece of BURNT BREAD, steeped in impure WATER, make it fit to drink?_

A. The surface of the bread is reduced to _charcoal_ by being burnt; and the charcoal surface of the bread _abstracts all the impurities of the water_, and makes it palatable.

Q. _Why should the TOAST and WATER, placed by the side of the sick, be made of BURNT BREAD?_

A. The surface of the bread being _reduced to charcoal_ by being burnt, prevents the water from being affected by the impurities of the sick room.

Q. _Why are TIMBERS, which are to be exposed to damp, CHARRED?_

A. _Charcoal undergoes no change_ by exposure to air and water; therefore timber will resist weather _much longer_, after it has been charred.

CHAPTER V.

LAMPS AND CANDLES.

Q. _Of what are OIL, TALLOW, and WAX composed?_