Results:No two of the flames looked exactly alike, but they all had some things
incommon.The candle flame was mostly yellow, but thecentralportionwas
blue. The alcohol flame was very blue (if the wickofyour burnerwas clean)
but it, too, had a central,brighterblue cone. The gas flame (if the stove was in
good working order) was blue also, but itscentralcone was even more distinct.
These differences were due to the fact thatyou wereburningdifferent fuels.
However, if you remember the definitionofa fuel (page 63), you know that
they are usually hydrocarbonsand produce carbon dioxide (and/orcarbon
monoxide) and watervaporwhen burning. Thecentralcones form as a result
ofan incomplete supply of oxygen. The fuel burns best at itsouteredges,
where it comes incontactwithair-thatis where it gets the oxygen it needs.
In the centerofthe flame, the gases are incompletelyburnedorhardlyburned
at all.Thatis why you could lead them offthroughthe glass tube and burn
them again at the nozzle end.
The hottestpartofany flame is directly above the inner cone. Canyou
guess why? When the flameofa hydrocarbonis yellow, or when the inner cone
is very large incomparisonwith theouterone, the fuel is not being completely
burned. This means waste,andwaste is expensive. This would be a good time to
check your gas stoveandask yourparentsto have it fixed if it isburningyellow.
HOWYOUCANSHOWTHATFIRESNEEDAIR
Gather these materials:Two small glasses; 2 large glasses; 2 glasschimneys;
6 birthdaycandles;and 9 corks.
Follow this procedure: On a fireproof portion ofyour laboratorytable,
arrangethe candles sothatthey areabout8 inchesapart.Fastenthem to the
table with their own wax, so theywon'tfall overduringthe experiment.Arrange
the piecesofglassware as follows: a small glass behind eachofthe first two
candles, a large glass behind eachofthe next two candles, and a glass chimney
behind eachofthe last two candles. Put three corks near the second,fourth,
and sixth candles. Light candle No. 1.Cover it with the small glass, inverted.
Notethe behaviorof the flame. Light candleNo.2.Arrangethe corks in a
trianglearoundits base and place the glass on the corks. Watch the flame and
see how it behaves.Repeatthisprocedurewith theremainingcandles and the
glassware behind them. Each time observe thebehaviorofthe flames,andat the
end,compareyourobservations.
Results:In the glassesthatdidn'trest on corks, the flames wentoutrather
quickly. The large glass, however, allowed the flame toburnlongerthanthe
small one did. In the glasses resting on corks, it is possiblethatthe flamesdidn't
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