Or he can tape or glue or tie a range objects - chunk of steel wool, 5 types of screws, a nail or 3 to a cardboard piece; immerse that in the tupperware container. Do the same layout for half a dozen type of water. The trick is, the metals cant touch each other. If they do (randomly) there may be a secondary effect from dissimilar metals touching in some cases that would distort the result. Be sure they dont come loose when you slosh the container to re-wet the metals.
Oh, and since no one said it yet (and this is the SDMB), since he’s going to be intentionally handling rusty metal everyday for the next 45 days (unless you mount it to something)…if anything is at all sharp, it might not be a terrible idea to make sure he’s up to date on his tetanus shots. Since he’s in 4th grade, I’m sure he is, but getting a copy of that from the doctor might be a nice little bit of above and beyond/extra credit for the judge/teacher.
If he’s a precocious he could even make the call himself to ask for a copy of his immunization record and when he’s due for his next tetanus booster.
The chances of getting tetanus from rusty metal are no higher than from anything else; the myth comes from the fact that objects like nails (which are often rusty when lying on the ground, but rust has nothing to do with tetanus bacteria, which live just about everywhere, including on your skin) are particularly prone to cause tetanus, but it is only because the bacteria need an anaerobic environment, as found in puncture wounds.
I did not know that. However, I did look it up on a few other sites to confirm it since that is a horribly written article.
Use ordinary bright nails (tin coated). Drop into a screw-top jar half filled with a variety of liquids. Screw the lids shut. Results within a week.
Liquids to try:
tap water
distilled water
boiled water – no dissolved oxygen
nail fully immersed
nail fully immersed with thin layer of oil on top
salt water
It should be easy to show that a combination of water and available oxygen is required for rusting and that salt accelerates the corrosion process in this case.
Daily photos would be the simplest method for recording the process.
(Metallurgical engineer and secondary school science teacher – done this expt many times.)
If you are going to be using steel wool, you might want to dissolve the lacquer coating off of it with acetone prior to attempting to rust it.
So we started the project yesterday and used 3 different waters:
- Ocean water
- Pond water
- Tap water
- Bottled water
- Tonic water
I bought a long ungalvanized steel rod and chopped it into pieces, had him scar up the metal with a file and dropped them into baby food jars with the water right away.
Several things are noteworthy after only 24 hrs:
-
The 4 rods that are rusty started rusting right away. Like within an hour you could see the red rust on the rods. Now they are already very rusty with nice harsh rusty areas on them. Happy about this but more interesting (to me)…
-
One of the rods hasn’t rusted at all. I mean AT ALL. Still looks totally new this morning like it just came off the shelf. It’s the Tonic Water. Hasn’t rusted at all.
Anyone have any idea why that may be? I was expecting them all to at least rust a little.
Poking 'round yon internet, it seems that quinine interferes with oxidation. Tonic water contains quinine.
don’t tell the young cub, let him practice reasoning and fact finding for a bit.
Are you documenting the experiment with photos? You could also run a inexpensive camera that captures video, Speed it up later to show the rusting in time lapse.
A security cam is ideal for capturing the video inexpensively.
go to the auto parts store and get a few cheap pieces of exhaust pipe. I think you can still find a lot of generic stuff that is non-aluminized and non-galvanized.
a couple of jobs ago I worked for a test lab in which one of the tests we offered was salt fog testing per ASTM B-117. After a day in a salt fog, plain steel items would be holy bejeezus rusted.
Did you miss the part where the op was made eight months ago and how it was just reanimated now to ask about the first result of the experiment? He’s not going to run out and restart with exhaust pipe.
I did indeed.
The tonic water corrosion resistance is an cool thing to accidentally find, congratulations. I’d have guessed it would rust fastest.
As mentioned, it appears quinine is providing the anti-corrosive properties. Also note that tonic water has some sodium which I think is working against the quinine. I’m not sure because it isn’t sodium chloride. It would be interesting to make a quinine-free tonic to see the samples side by side.
the thread was started 11-03. 1 month ago. 
The OP posted today that they started the experiment yesterday. Which is why I suggested capturing it on video, for a time lapse vid later.
I’m not sure how a 30 day time lapse vid would work. Somehow you’d have to edit together several videos. Then speed it up so that 30 days is shown in 1 min.
methinks naita is reading it in the non-US way (day-month-year.)
Nuhu! The date has been forged to make me look foolish! 
ETA: I did think it was a bit odd to plan school projects that far ahead…