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The "burning candle" experiment may have been largely replaced by the 
"rusting steel wool" experiment.  I would think the latter may actually be 
pretty good for demonstrating that air is roughly 20% oxygen.  But it takes 
several days, I believe.

Our testing of the "burning candle" experiment with teachers in Zanzibar 
some 15 yy ago generated a lot of good discussion about chemistry and 
physics and good thinking about experimental method and reproducibility and 
design.  I think a lot more learning happened than would have had we done 
the "rusting steel wool" experiment instead.

----Original Message Follows----
From: "Robert V. Lange" <[log in to unmask]>
Reply-To: Science for the People Discussion List              
<[log in to unmask]>
To: [log in to unmask]
Subject: burning candle esperiment
Date: Sat, 21 Jul 2007 17:39:42 -0400


Actually the burninig candle experiment is a great opportunity to introduce 
careful experimentation into the classroom.? Of course the usual 
interpretation is false.?? Eric Entemann and I and Mike Savage introduced 
this experiment in a workshop for teachers in Zanzibar.? Eric made a 
sparking device and was able to light the candle after the beaker was 
already firmly placed over the candle and in the water.? Of course, the 
candle went out long before the water level went up at all.? Obviously CO2 
takes up as much space as O2, and oxygen is simply replace by the gases 
given off in combustion.? And besides, there is still lots of oxygen in the 
beaker when the candle goes out anyway.? Combustion requires more than 
simply the presence of an O2 molecule or two.

The entire effect is due to the heating of the air around the candle before 
you put the beaker over it.? We and the teachers were able to get the water 
to rise up much further than one fifth by manipulating the air heating and 
the way we put the beaker on, and by having more than one candle, etc.

So rather than worry about expunging this falsely interpreted experiement, 
couldn't we consider it an opportunity to raise issues about interpretation, 
about having observation and interpretation being colored by apriori 
assumptions, and all that??? It should be kept as an example of false 
interpretation that is very educaitonal, maybe more educational then just 
the "right answer".

bob (lange)



-----Original Message-----
From: herb fox <[log in to unmask]>
To: [log in to unmask]
Sent: Sat, 21 Jul 2007 5:18 pm
Subject: Expunge the burning candle experiment from science TEXTBOOKS


Dear friends:
??? There is a cute "demonstration" that air is 20% O2 wherein a burning 
candle in an overturned glass on a saucer of water is extinguished by virtue 
of consuming 20% of the included volume of air.? Hopefully most of you know 
that the demonstration is a fraud.? In spite of the authenticity of the 
demonstration having been questioned since the mid 19th century, it still 
appears unquestioned in some elementary science, physical science and 1st 
year chemistry textbooks.
??? Sudipta Saraswati has written papers on various aspects of this myth 
from analytical and experimental demonstrations of its falsity to 
discussions of the persistence of science myths long after they are 
discredited.? At this point he is frustrated in his search for US textbooks 
that perpetuate the myth, primarily because of his limited access to the 
texts, not to mention the inappropriateness of writing publishers to 
identify texts from their catalog that are in error.
??? Dr Saraswati's email to me is attached.? I believe his work is important 
and would very much appreciate responses to his request.? Please respond to 
him directly at [log in to unmask]
thank you
herb fox





Attached Message




From:

Sudipta Saraswati <[log in to unmask]>



To:

herb fox <[log in to unmask]>



Cc:

Sudipta Saraswati <[log in to unmask]>



Subject:

Seeking your help in my search for the burning candle experiment in American 
school science TEXTBOOKS



Date:

Wed, 18 Jul 2007 22:43:34 -0400







Dear Herb,

As I explained to you during our meeting earlier, in spite of the best
of my efforts, I have not yet managed to get an access to
middle and high school physical science TEXTBOOKS in Boston to find out 
whether
the burning candle experiment (described below), which is being 
misinterpreted
in many countries including India and Britain, is featured in American 
school
science textbooks.

A typical description of the burning candle experiment is as follows:
Place a burning candle at the center of a shallow pool of water and then 
cover
it with an inverted beaker. Eventually, the candle goes out and the water 
level
rises to occupy approximately 20% of the beaker. It is claimed that this 
proves
that the proportion of oxygen by volume in the air is 20%.

It will be of great help for me if you could kindly request a few of your 
school
science teacher friends to browse through middle and high school textbooks 
of
physical sciences to look for whether the burning candle experiment is 
featured
in any of those as an experiment to measure the percentage of oxygen in the
air.

Looking forward to hearing from you.

Thank you.

Best regards,

Sudipta
-------













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