Ferro fluid experiment safe?
February 14, 2010 8:25 AM   Subscribe

Is this experiment safe to try with my students?

I'm not a science teacher, but at the end of the month if everyone's worked hard we try and do one or two special things as motivation. One student (this is Junior High) really wants to try this experiment (how to make magentic fluid – ferro fluid).

It looks messy, and I don't know if we'd have to wear face masks or if there are any toxins involved here.

If there's a simpler version of this experiment, that would be better! Thanks for any help.
posted by fantasticninety to Education (16 answers total) 9 users marked this as a favorite
 
Best answer: The experiment is simple.

As for toxins, the only conceivable thing in that experiment that would be dangerous is inhalation of the printer toner powder or broken glass.

Rare earth magnets and vegetable oil are not dangerous, nor is glassware properly handled, nor is printer toner that is not inhaled.
posted by dfriedman at 8:31 AM on February 14, 2010


Let me amend my statement about rare earth magnets.

Rare earth magnets of the size shown in the video are not dangerous. Large rare earth magnets can be dangerous if, for example, you hold one too close to another large one and the magnetic force between the two crushes your hand.

Rare earth magnets will also destroy credit cards (possibly a benefit, depending upon your view of credit card debt) and ruin CRT monitors.
posted by dfriedman at 8:38 AM on February 14, 2010


That is beyond cool! But someone is going to ruin their uniform. I'd get a permission slip signed ahead of time to avoid the angry parent who has to go buy new clothes. Also, have the kids wear trash bags over their clothes and get some baby wipes for small spills and hand-wiping.
posted by debbie_ann at 9:08 AM on February 14, 2010


The other danger with rare earth magnets is when you swallow them. In fact, the ones I've bought came with a specific warning about the quite nasty things they can do to your innards (i.e. stick together and rip holes in your digestive tract).

And of course it'll be rather messy, so gloves and an apron might be wise.
posted by le morte de bea arthur at 9:17 AM on February 14, 2010


Looks pretty safe and it's most definitely cool, but why does it work? Why is toner magnetic? What makes the ferro fluid shapes the way they are? You owe it to your students to at least have these explanations on hand, even if you're not planning on making it a lecture.

Have fun :)
posted by DavidandConquer at 9:27 AM on February 14, 2010


As to what a ferrofluid is: wikipedia has a good explanation.

Here: http://en.m.wikipedia.org/wiki/Ferrofluid?wasRedirected=true

Possibly above a junior high school student's comprehension.
posted by dfriedman at 10:23 AM on February 14, 2010


just know that spilled toner is a pain in the ass to clean up.
posted by dogwelder at 11:23 AM on February 14, 2010


Best answer: When it comes time to clean up toner, be sure to use COLD water. Heat fuses toner; hot water will just fuse it to whatever you're trying to wash.
posted by reeddavid at 11:44 AM on February 14, 2010


I'd make a couple of minor changes to the procedure if I were doing it with a group.

1. I'd use mineral oil instead of vegetable oil. Mineral oil doesn't go rancid, so you could store the fluid afterward and reuse it.

2. I'd mix up the fluid ahead of time, rather than having the students do it. Powdered toner is a mess to deal with, and inevitably someone will spill it, or get some on their hands, and then it'll be all over the place and all over everyone's clothes. Assuming your students know how to mix 200mL of something with 2 Tbsp (interesting choice of units in the video) of something else, it's not like they'd really be missing much by just getting a vial of the stuff from you. Maybe you could do a batch in front of everyone and then pass it out.

3. I'd think very seriously about handing out the ferrofluid in sealed containers that the students don't have to open to complete the experiment. There's nothing going on in the video that requires the flask to be open; it would work just as well if it were closed. Then you'd have zero risk of the stuff ending up all over the magnets and the students and your classroom and probably the ceiling.

I do wonder though, whether really understanding what's going on — at anything more than a "gee whiz that's neat" parlor-trick level — would be beyond the level of most junior high students. I'm all for making science and physics more interesting, but I question the value of just looking at ferrofluid in a magnetic field without really understanding why the ferrofluid is behaving in the way that it is, how its density is changing, what magnetic flux is ... it would be a good intro to an in-depth discussion, but without that in-depth discussion I tend to question the value. So if your students aren't up for the theory, there are probably more meaningful — and equally impressive — experiments that would fit in with the curriculum better.

A brief anecdote: When I was in junior high, someone made the decision to buy a — I can only imagine astoundingly expensive — high-temperature superconductivity demonstration setup. It had two tiny cuprate superconductors and a CCTV camera with a macro lens so that everyone could see what was going on. You poured liquid nitrogen over them and, if everything went right and you had a steady hand, you could get one conductor to levitate and spin above the other one. It was impressive. But then someone asked a question about why it was happening, and … (cue crickets). I don't think anyone in the room really understood why it was happening, at least in any way that they could explain to the students. (I don't blame or fault them for this; I still found it to be mindfuck-worthy when I was an undergrad taking solid state for the first time, years and thousands of hours of class time later.) The end result was a lot of confusion all around, until someone started freezing things in the remaining liquid nitrogen and shattering them; the HTSC setup literally pushed aside.
posted by Kadin2048 at 1:00 PM on February 14, 2010 [4 favorites]


I'd also think about maybe putting the ferrofluid into plastic bags (maybe something heavier; tied-off latex gloves?) and letting the students see how it reacts to multiple magnets. Most practical uses of ferrofluids involve putting it between multiple magnets, and then taking advantage of how its density changes in response to flux. I've never used the MICR toner + oil fluid, but I'd imagine you'd be able to feel this effect with a couple of magnets.
posted by Kadin2048 at 1:04 PM on February 14, 2010


THIS IS A HOAX. Do not try to make it. It will not work.

Everything "Household Hacker" does is fake. He's been at it for years. (Here's a bit I wrote about him a while ago.)

Some of the Household Hacker parodies are so over-the-top that it should be obvious to any thinking human that it's a joke, but then there are ones like this that someone who doesn't have the appropriate knowledge could take for real.

In this case, the problem is that laser-printer toner contains only plastic and carbon black, and is therefore not magnetic. Mix it with oil, also not magnetic, and all you get is black oil. He just swapped in real, store-bought ferrofluid for the latter part of the video.

It is possible to make your own ferrofluid, or something at least somewhat like it, but you need to mix something that's actually ferromagnetic into the oil:
http://www.instructables.com/id/Make-your-own-ferrofluid-in-5-minutes/
http://www.popsci.com/diy/article/2009-09/making-ferrofluids-work-you
posted by dansdata at 3:24 PM on February 14, 2010 [4 favorites]


Good catch dandata!

Basically the instructables article is the same as teh hoax, but it replaces the laser toner w/ real magnetic ink.
posted by DavidandConquer at 4:04 PM on February 14, 2010


You guys, maybe I'm dumb, but maybe this one isn't fake?

Both links mention using MICR stuff.

And a search for MICR toner seems to get a ton of hits selling normal printer toner.

Yeah, I believe his other stuff is fake, but could this possibly be real?

Otherwise, convincing fake, household hacks! Congratulations. You got me.
posted by R a c h e l at 4:32 PM on February 14, 2010 [1 favorite]


Ok Rachael, now I'm back on board with you in the "not fake" camp.

I missed in the video how he is using MICR toner (he never says it, but her shows it and lists it in the video description). All he says is "laser toner" which as dansdata points out, usually has only a polymer in it to stick to the static electric charge.
posted by DavidandConquer at 4:54 PM on February 14, 2010


In the Olden Days, when dinosaurs and saber-tooth tigers roamed, we did something similar with iron filings sprinkled on a piece of paper and a bar magnet held underneath. Same principle, though not nearly as kewell.
posted by exphysicist345 at 5:16 PM on February 14, 2010


Yes, he does depict, though not identify, a MICR toner bottle at the beginning of the video clip. If the fluid he demonstrates is actually the fluid he made, though, I for one will eat the hat of your choice. It is not possible to make ferrofluid that works that well, that easily.

This, the Instructable I linked above, is some real MICR-ink ferrofluid. Note the ugly iron-filing-like spikes. Here's some that was made using the ferrite coating from old tapes dissolved in acetone; it also illustrates the principle passably well, but it's a sludgy mess compared with "proper" ferrofluid.

Proper ferrofluid does not just have tiny magnetic particles in it; the particles also need to have a surfactant coating so they can't clump together. Toner has no such coating.

There's also, as mentioned at the end of this page, a narrow range of particle sizes that will work. If the particles are too big, they come out of suspension; I think this is the usual problem with home-made ferrofluid. You have to keep stirring it up, and oil drips out of it when you magnetise it, giving rise to the "dry" spikes. If the particles are too small (if you made them with some chemical reaction that has a ferromagnetic precipitate, for instance), the fluid won't react to magnetism at all.

(I wrote some stuff about ferrofluid years ago, by they way.)

The surfactant coating makes the nanoscale particles in ferrofluid somewhat conceptually similar to the much larger particles of "Magic Sand". You can definitely make decent Magic Sand at home, since it's basically just ordinary clean sand (brightly coloured, in the commercial product) with a hydrophobic silicone coating. Water-repelling spray for clothes, like Scotchgard, will do the job on ordinary sand; here's a video tutorial.
posted by dansdata at 5:23 PM on February 14, 2010 [1 favorite]


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