CHAPTER XIV.. 2.--Absorption of Heat.

2.--ABSORPTION OF HEAT.

Q. What is the difference between CONDUCTING heat, and ABSORBING heat?

A. To conduct heat, is to transmit it from one body to another through a conducting medium: to absorb heat, is to suck it up, as a sponge sucks up water.

Q. Give me an example.

A. Black cloth absorbs, but does not conduct heat: thus, if black cloth be laid in the sun, it will absorb the rays very rapidly; but if one end of the black cloth be made hot, it would not conduct the heat to the other end.

Q. Are good CONDUCTORS of heat, good ABSORBERS also?

A. No; every good conductor of heat is a bad absorber of it; and no good absorber of heat can be a good conductor also.

Q. Is IRON a good ABSORBER of heat?

A. No; iron is a good conductor, but a very bad absorber of heat.

Q. Why do the FENDER and FIRE-IRONS (which lie upon it) remain COLD, although they are before a good fire?

A. Because the metal fender and fire-irons have very little capacity for absorbing heat; although they are soon made hot (by conduction), when placed in contact with the hot fire or stove.

Q. Why does a KETTLE boil faster, when the bottom and back are COVERED with SOOT?

A. The black soot absorbs heat very quickly from the fire, and the metal conducts it to the water.

Q. Why will not a NEW KETTLE boil so fast as an OLD one?

A. Because the bottom and sides of a new kettle are clean and bright; but in an old kettle are covered with soot.

Q. Why would the KETTLE be SLOWER BOILING, if the BOTTOM and BACK were CLEAN and bright?

A. Bright metal does not absorb heat, but reflect it (i. e. throw the heat back again); and as the heat is thrown off from the surface of bright metal, therefore, a new kettle is longer boiling.

Q. Why do we wear WHITE LINEN and a BLACK outer DRESS, if we want to be warm?

A. The black outer dress quickly absorbs heat from the sun, and conveys it to the body; and the white linen (being a bad absorbent) abstracts no heat from the warm body.

Q. Why do persons WEAR WHITE dresses in SUMMER time?

A. White throws off the heat of the sun by reflection, and is, therefore, a very bad absorbent of heat; in consequence of which, it never becomes so hot from the scorching sun as dark colours do.

Q. Why do NOT persons WEAR WHITE dresses in WINTER time?

A. White will not absorb heat, like black and other dark colours; and, therefore, white dresses are not so warm as dark ones.

Q. What COLOURS are WARMEST for dresses?

A. For outside garments black is the warmest, and then such colours as approach nearest to black (as dark blue and green). White is the coldest colour for external clothing.

Q. Why are DARK COLOURS (for external wear) so much WARMER than LIGHT ONES?

A. Because dark colours absorb heat from the sun more abundantly than light ones.

Q. How can you prove that DARK colours are WARMER than LIGHT ones?

A. If a piece of black cloth and a piece of white were laid upon snow, in a few hours the black cloth will have melted the snow beneath; whereas the white cloth will have produced little or no effect upon it at all.

N. B. The darker any colour is, the warmer it is, because it is a better absorbent of heat. The order may be thus arranged:--1. Black (warmest of all).--2. Violet.--3. Indigo.--4. Blue.--5. Green.--6. Red.--8. Yellow: and 9. White (coldest of all).

Q. Why are BLACK KID GLOVES so HOT in summer time?

A. 1st--Because the black absorbs the solar heat: and

2ndly--The kid will not allow the heat of the hand to escape through the glove.

Q. Why are LISLE THREAD GLOVES so COOL in summer time?

A. 1st--Because thread absorbs the perspiration of the hands: and

2ndly--It conducts away the heat of our hot hands.

Q. Are Lisle thread gloves ABSORBENTS of heat?

A. As Lisle thread gloves are generally of a grey or lilac colour, they do not absorb solar heat.

Q. Why is a PLATE-WARMER made of UN-PAINTED BRIGHT TIN?

A. Bright tin reflects (or throws back) the heat, which issues from the fire in rays; and (by reflecting the heat upon the meat) assists greatly in roasting it.

Q. Why would not the tin REFLECTOR do as well if it were PAINTED?

A. If the tin reflector were painted, it would be utterly spoiled, because it would then absorb heat, and not reflect it at all. A plate-warmer should be kept very clean, bright, and free from all scratches.

Q. Why should a REFLECTOR be kept so very CLEAN and free from SCRATCHES?

A. If a reflector be spotted, dull, or scratched, it will absorb heat, instead of reflecting it; and, therefore, would be of no use whatsoever as a reflector.

Q. Why does HOAR-FROST remain on TOMBSTONES, long after it has melted from the GRASS and GRAVEL-WALKS of a church-yard?

A. Tomb-stones being white, will not absorb heat, like the darker grass and gravel; and, therefore, the white tombstones (being so much colder) retain the hoar-frost after it has melted from other things.

Q. If black absorbs heat, why have those who live in HOT climates BLACK SKINS, and not WHITE skins (which would not absorb heat at all)?

A. Though the black skin of the negro absorbs heat more plentifully than the white skin of a European, yet the blackness prevents the sun from blistering or scorching it.

Q. How is it known that the BLACK colour prevents the sun from either BLISTERING or SCORCHING the skin?

A. If you put a white glove on one hand, and a black glove on the other (when the sun is burning hot), the hand with the white glove will be scorched, but not the other.

Q. Which hand will FEEL the HOTTER?

A. The hand with the black glove will feel the hotter, but it will not be scorched by the sun; whereas the hand with the white glove (though much cooler) will be severely scorched.

Q. Why does the BLACK skin of a NEGRO NEVER SCORCH or BLISTER with the hot sun?

A. Because the black colour absorbs the heat,--conveys it below the surface of the skin, and converts it to sensible heat and perspiration.

Q. Why does the WHITE EUROPEAN SKIN BLISTER and SCORCH when exposed to the hot sun?

A. Because the white will not absorb the heat; and, therefore, the hot sun rests on the surface of the skin, and scorches it.

Q. Why has a NEGRO BLACK EYES?

A. The black colour of a negro's eyes defends them from the strong light of the tropical sun. If a negro's eyes were not black, the sun would scorch them, and every negro would be blind.

Q. Why is WATER KEPT COOLER (in summer time) in a BRIGHT TIN POT, than in an EARTHEN one?

A. Because bright metal will not absorb the heat of the summer sun, like an earthen vessel.

Q. Why is BOILING water KEPT HOT in a BRIGHT TIN VESSEL longer, than in an earthen one?

A. Because bright tin will not suffer the heat of the boiling water to escape in rays, as an earthen vessel does.