Candles, jars and water
Marcus Houlden
I heard in yesterday's news about an alternative explanation for the
experiment where water rises inside a glass jar if a candle has been
burning inside it. The explanation I was given at school was that the
oxygen in the jar was burnt off and the space where the oxygen was was
filled up by water. However, it now seems that it happens because the
air in the jar gets hot and it cools down (and contracts) when the
candle burns out. Any comments on this?
--
Marcus Houlden
http://www.bigfoot.com/~Marcus.Houlden Marcus....@bigfoot.com
http://members.xoom.com/mhoulden Marcus....@stud.umist.ac.uk
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Sherilyn
In article <35701ABA...@bigfoot.com>, Marcus Houlden
<Marcus....@bigfoot.com> writes
>I heard in yesterday's news about an alternative explanation for the
>experiment where water rises inside a glass jar if a candle has been
>burning inside it. The explanation I was given at school was that the
>oxygen in the jar was burnt off and the space where the oxygen was was
>filled up by water. However, it now seems that it happens because the
>air in the jar gets hot and it cools down (and contracts) when the
>candle burns out. Any comments on this?
To eliminate this effect, use a large jar and a small candle.
--
Sherilyn|Had a premonition lately? Get it registered! Get it noticed!
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Luser 7
In article <VIpG90AlnFc1Ew$P...@sidaway.demon.co.uk>, Sherilyn
<Sher...@my-dejanews.com> wrote:
#In article <35701ABA...@bigfoot.com>, Marcus Houlden
#<Marcus....@bigfoot.com> writes
#>I heard in yesterday's news about an alternative explanation for the
#>experiment where water rises inside a glass jar if a candle has been
#>burning inside it. The explanation I was given at school was that the
#>oxygen in the jar was burnt off and the space where the oxygen was was
#>filled up by water. However, it now seems that it happens because the
#>air in the jar gets hot and it cools down (and contracts) when the
#>candle burns out. Any comments on this?
#
#To eliminate this effect, use a large jar and a small candle.
#--
#Sherilyn|Had a premonition lately? Get it registered! Get it noticed!
#misc.predictions.registry http://www.manx2.demon.co.uk/news/faq.htm
You haven't completely described the experiment. I am interpreting this
as follows:
A glass jar is inverted and immersed in water with and without having
a candle burned in it first.
When the candle is burned in the jar, the air (or smoke) under
the jar is hot. Hot gas is less dense at the same pressure, so there is
actually less in the jar. When it's cooled down by placing it in water,
the temperatures are equalized and the jar with less gas in it has a
smaller bubble.
As a minor aside, a lot of the hot gas in the jar is water vapor (steam)
produced by burning the hydrogen in the candle wax. Most of the vapor
probably condenses out when it's cooled and this exaggerates the
effect.
Luser 7
Sherilyn
In article <luser-ya02408000...@news.idt.net>, Luser 7
<lu...@home.com> writes
So using a large jar and a small candle will reduce this effect.
>
>As a minor aside, a lot of the hot gas in the jar is water vapor (steam)
>produced by burning the hydrogen in the candle wax. Most of the vapor
>probably condenses out when it's cooled and this exaggerates the
>effect.
Ditto, as it happens.
--
Sherilyn|Had a premonition lately? Get it registered! Get it noticed!
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Matthew Wootton
>>I heard in yesterday's news about an alternative explanation for the
According to New Scientist, the oxygen burnt off becomes carbon dioxide
of similar density - meaning that what you were taught at school was
bull.
--
Matthew Wootton
Ron Hunsinger
In article <3fJbzAAA...@akooka.demon.co.uk>, Matthew Wootton
<ma...@akooka.demon.co.uk> wrote:
> According to New Scientist, the oxygen burnt off becomes carbon dioxide
> of similar density - meaning that what you were taught at school was
> bull.
Assuming you're burning a hydrocarbon, some of the oxygen combines with
carbon to make carbon dioxide (C + O2 = CO2), which makes no net change in
the number of gas molecules. But you also have some of the oxygen combining
with hydrogen to make water, which then condenses out as liquid. (If it
didn't, you'd actually have an increase in the number of gas molecules. 4H
+ O2 = 2H2O).
But some of the oxygen does go into making water (and also some of the CO2
produced will dissolve in the water), so you should wind up with some
decrease in volume, largely for the reason given by your high school
teacher.
-Ron Hunsinger
Sher...@my-dejanews.com
>
> According to New Scientist, the oxygen burnt off becomes carbon dioxide
> of similar density - meaning that what you were taught at school was
> bull.
Diatomic O2 is replaced by molecular CO2. By Avogadro's Law,
they occupy the same volume. (22.4 l/mole at stp if my
alchemy teacher was right--yep, I left school that long ago!).
The only description of the demonstration I could find on the WWW
made a special note of the formation of water vapor on the inside
of the jar. This is correct. The only net reduction in volume
would be from oxidations that produce non-gaseous compounds--
primarily condensed water vapor.
http://personal.cfw.com/~rollinso/SciPhys.html
Use a large jar to reduce thermal expansion effects.
--
Sherilyn
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John Holmes
Sher...@my-dejanews.com wrote in message
<6l350k$k4n$1...@nnrp1.dejanews.com>...
[snip]
>The only description of the demonstration I could find on the WWW
>made a special note of the formation of water vapor on the inside
>of the jar. This is correct. The only net reduction in volume
>would be from oxidations that produce non-gaseous compounds--
>primarily condensed water vapor.
That sounds reasonable to me, but I also wonder about other non-gaseous
products. A candle flame is a fairly inefficient means of combustion,
particularly as the oxygen in the jar is being depleted. Won't there
also be some partially burnt hydrocarbons-- sort of tarry sooty gunk
deposited on the inside of the jar? Doesn't candlewax contain some
aromatics (i.e. with C6 rings) which aren't going to burn so readily all
the way to CO2 and H2O?
Can any organic chemists comment?
(I agree, though, that the main volume reduction is caused by the
cooling of the air.)
Regards,
John.
hol...@smart.net.au
email copies of any replies would be appreciated.
Carl Fink
On Thu, 4 Jun 1998 05:50:32 +1000, John Holmes <hol...@smart.net.au> wrote:
>That sounds reasonable to me, but I also wonder about other non-gaseous
>products. A candle flame is a fairly inefficient means of combustion,
>particularly as the oxygen in the jar is being depleted. Won't there
>also be some partially burnt hydrocarbons-- sort of tarry sooty gunk
>deposited on the inside of the jar? Doesn't candlewax contain some
>aromatics (i.e. with C6 rings) which aren't going to burn so readily all
>the way to CO2 and H2O?
Yes, but so what? Would there be a volume change if long-chain
hydrocarbons in the candle become shorter-chain hydrocarbons (and
presumably alcohols and whatnot) on the surface of the jar?
--
Carl Fink ca...@dm.net
Q. Why do some people take astrology seriously?
a. Because they have unusually small brains. --Dave Barry
John Holmes
Carl Fink wrote in message <6l4vlj$1kt$1...@carlf.dialup.access.net>...
>On Thu, 4 Jun 1998 05:50:32 +1000, John Holmes <hol...@smart.net.au>
wrote:
>>That sounds reasonable to me, but I also wonder about other
non-gaseous
>>products. A candle flame is a fairly inefficient means of combustion,
>>particularly as the oxygen in the jar is being depleted. Won't there
>>also be some partially burnt hydrocarbons-- sort of tarry sooty gunk
>>deposited on the inside of the jar? Doesn't candlewax contain some
>>aromatics (i.e. with C6 rings) which aren't going to burn so readily
all
>>the way to CO2 and H2O?
>Yes, but so what? Would there be a volume change if long-chain
>hydrocarbons in the candle become shorter-chain hydrocarbons (and
>presumably alcohols and whatnot) on the surface of the jar?
Well, if they use up some of the oxygen in doing so, it might contribute
slightly to a volume reduction. I wasn't suggesting it was anything
major.