Re: Boyle's Law and how to demonstrate it

Doug,
here are a few examples that may work for you.

1)  automobile engine.  The volume of the cylinder is constant (piston at 
rest) when the gas/air mixture is initially ignited.  The pressure rises 
in this region because several molecules of gaseous products are formed 
from a smaller number of molecules of air and gasoline.  the force of the 
gas pressure pushed the piston out (volume increasing) until the end of 
the stroke (envision the crankshaft).  Another set of cylinders fires at 
this point, driving the piston upwards decreasing the volume and 
compressing the gas in the cylinder.  this "push" removes the combustion 
products.  This example shows the balance between pressure and volume.

2)  2L soda bottle crush.  Pass around an empty (and sealed) 2L soda 
bottle.  Ask students to crush it...they'll have a problem doing it.  Pour 
boiling water in, cap the bottle quickly, and immerse in a cold water 
bath.  Try this out before demo-ing, but it should work.  I've seen this 
done with paint thinner cans too.  What happens is that the water vapor 
condenses, dropping the pressure inside the bottle.  The volume of the 
bottle changes to accomodate the pressure difference.

3)  potato chips on the airplane.  Airplane cabins are pressurized at less 
than atmospheric pressure.  At 35000 feet (fairly typical cruising 
altitude for a large airliner), atmospheric pressure is probably about 50% 
or less that at sea level.  Food that is packaged at sea level and sealed 
will then expand against the lower pressure in the cabin of the plane.

make sure to check out:  UofWisconsin

It is a great UofWisconsin site with descriptions of many useful demos.  
The expanding marshmallow is a favorite of mine.  Shakashiri's book 
(referenced there in many places) is the classic book on chem demos.

Hope this works for you.  feel free to email me at weibelm@battelle.org if 
you have further questions.

Best Regards,
Mike