A Guide To The Scientific Knowledge Of Things Familiar Part 44

A. Yes; and because _burning fuel emits rays of heat_, therefore we _feel warm_ when we stand before a fire.

Q. _Why does our FACE FEEL uncomfortably HOT, when we approach a FIRE?_

A. Because the fire radiates heat upon the face; which (not being _covered_) feels the effect immediately.

Q. _Why does the fire catch the FACE more than the REST of the body?_

A. The _rest_ of the body is _covered with clothing_, which (being a _bad conductor_ of heat) prevents the same sudden and rapid transmission of heat to the skin.

Q. _Do those substances which RADIATE heat, ABSORB heat also?_

A. Yes. Those substances which _radiate most_, also _absorb most heat_: and those which _radiate least_, also _absorb the least_ heat.

Q. _Does any thing ELSE radiate heat, BESIDES the SUN and FIRE?_

A. Yes; _all_ things radiate heat in _some_ measure, but _not equally well_.

Q. _What things RADIATE heat the NEXT BEST to the sun and fire?_

A. All _dull_ and _dark substances_ are _good radiators_ of heat; but all _light_ and _polished substances_ are _bad radiators_ of heat.

Q. _Why does a POLISHED METAL TEA-POT make BETTER TEA than a black earthen one?_

A. As polished metal is a very _bad radiator_ of heat, it _keeps the water hot much longer_; and the hotter the water is, the better it "draws" the tea.

Q. _Why will not a DULL BLACK TEA-POT make good tea?_

A. Because the heat of the water _flies off so quickly_ through the dull black surface of the tea-pot, that the _water is rapidly cooled_, and will not "draw" the tea.

Q. _Do not pensioners, and most aged cottagers, prefer the little BLACK EARTHEN TEA-POT to the bright METAL one?_

A. Yes; because they _set it on the hob "to draw;"_ in which case, the little _black tea-pot_ will make the _best tea_.

Q. _Why will a BLACK TEA-POT make better tea than a bright metal one, if it be set upon the HOB to DRAW?_

A. Because the black tea-pot will _absorb heat plentifully_ from the fire, and keep the water _boiling hot_: whereas, a bright _metal_ tea-pot (set upon the hob) would _throw off_ the heat by _reflection_.

Q. _Then sometimes a BLACK EARTHEN tea-pot is the best, and sometimes a bright METAL one?_

A. Yes; when the tea-pot is _set on the hob "to draw,"_ the black _earth_ is the _best_, because it _absorbs heat_: but when the tea-pot is _not_ set on the hob, the bright _metal_ is the _best_, because it _radiates heat very slowly_, and therefore _keeps the water hot_.

Q. _Why does a SAUCEPAN which has been USED, boil QUICKER than a NEW ONE?_

A. Because the bottom and back are _covered with soot_; and the _black soot_ rapidly _absorbs the heat_ of the glowing coals.

Q. _Why should the FRONT and LID of a SAUCEPAN be clean and BRIGHT?_

A. As they do not come in contact with the fire, they cannot _absorb heat_; and (being bright) they will not suffer _the heat to escape_ by radiation.

Q. _In what state should a SAUCEPAN be, in order that it may BOIL QUICKLY?_

A. All those parts which _come in contact with the fire_ should be covered with _soot_, to absorb heat; but all the _rest_ of the saucepan should be as _bright as possible_, to prevent the _escape of heat_ by radiation.

Q. _Why is it said that "SAt.u.r.dAY'S KETTLE BOILS the FASTEST?"_

A. Because on Sat.u.r.day the _front_ and _top_ of the kettle are generally _cleaned_ and _polished;_ but the _bottom_ and _back_ of the kettle are _never_ cleaned.

Q. _Why should NOT the BOTTOM and BACK of a kettle be CLEANED and polished?_

A. Because they _come in contact with the fire_, and (while they are covered with black soot) _absorb heat freely_ from the burning coals.

Q. _Why should the FRONT and TOP of a kettle be CLEAN and well polished?_

A. Because polished metal _will not radiate heat_; and, therefore, (while the front and top of the kettle are well polished) _the heat is kept in_, and not suffered to escape by radiation.

Q. _Why is the INSIDE of a KETTLE and SAUCEPAN WHITE?_

A. _White will not radiate heat_: if, therefore, the inside of a boiler be _white_, the liquor in it is _kept hot much longer_.

Q. _Why is the BOTTOM of a KETTLE nearly COLD, when the WATER is BOILING HOT?_

A. Black soot is a very _bad conductor of heat_; and, therefore, the heat of the boiling water is some considerable time, before it gets _through the soot_ which adheres to the bottom of the kettle.

Q. _Why is the LID of a KETTLE so intensely HOT, when the water boils?_

A. The bright metal lid of the kettle _is an admirable conductor_ of heat; and, therefore, _the heat from the boiling water pours into our hand_ the moment we touch it.

Q. _Show the benefit of SMOKE in COOKING._