I hadn't actually done the Curie Point snack for several years, so I set it
up and tried it before writing you. I didn't have a large lantern battery, so
I tried it with four D cells in series (using a strand of wire from braided
picture hanging wire and an ordinary ceramic donut-shaped magnet). It didn't
work -- just as you said, the wire wouldn't get hot. I actually measured the
current, and was getting about 2.5 amps. Then I put a couple of C cells in
series with what I already had, and got up to 3.5 amps, but that didn't do it
either.
At this point, I broke down and got a 6 volt lantern battery as specified in
the materials list and shown in the picture with the snack. That gave me
around 7 amps, which made the wire glow red and released the magnet in less
than five seconds! I did it a few more times, and noticed that the current
went down to about 4 amps or less when the wire was glowing, which is
logical, since the hot wire has greater resistance than the cold wire.
Finally, I tried two stacks of four D cells, with the two stacks wired in
parallel, still giving 6 volts, but in theory giving more current capacity.
But I could only get a little over 4 amps maximum, which didn't heat the wire
enough. Maybe you can play around with even more D cells, but I'm not
optimistic.
So the bottom line is that the snack works with the large lantern battery.
The bad news is that the large lantern battery can now very expensive -- a
Duracell was almost $20 at one hardware store! Maybe you can shop around to
find the cheapest one available. Also there is a smaller size 6-volt lantern
battery that's cheaper -- maybe that might work, but I don't know.
Hope this helps. Let us know how things turn out!
Don Rathjen
Exploratorium Teacher Institute
donr@exploratorium.edu
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