Science by Mail, Packages 11-16

25 Sep 2008

Original Blogger tags: Science by Mail

More element samples and other nifty things to show to students.

Here is a sample for Carbon: a really magnificent, shiny, hand-filling piece of anthracite coal. Most young people living in 2008 have probably never handled a piece of coal, but it is stuff of great significance, since it is our biggest greenhouse gas producer and the source of most of our electricity.

I also already had some small pieces of natural graphite and some small pieces of jet, which is a coal-like substance that also formed from fossilized plant material, but wood in particular. Jet is very cool stuff and someday I’d like to stumble across a real Victorian-era necklace of genuine faceted hard jet pieces, but this mourning jewelry seems to have had a resurgence among modern goths, so the real stuff has become rather expensive. (If you want to find something really creepy, though, look for Victorian hair jewelry — not jewelry that goes in your hair, but jewelry made of hair).

But I digress, as usual. The next package contained a sample of crude oil. Given how important this is to our infrastructure and daily lives, you’d thing we’d be more familiar with the raw material, but just like we generally buy cartons of milk without seeing cows, we fill our cars with gas without seeing what the source material looks like. It’s thinner and runnier than you might expect. People used to drink it as a tonic. (NOTE: I can’t advise that.) We might pour some out so people can smell it and touch it.

Another stand-in for diamonds, these look even more like diamonds than the “Herkimer Diamond” quartz crystals. These are cubic zirconia. They actually look brighter and prettier than real diamonds, but don’t tell DeBeers. If the large one were real real it would be a 6.5 carat flawless cut diamond worth… well, Google diamond prices for yourself. Let’s just say I could probably retire. The fake one cost me $10.

Next up, a sample of gallium. Gallium is a metal that melts at about 86 degrees Fahrenheit. In other words, it melts in your hand, although it might take a long time to get it to melt completely. My sample came in a polyethylene bag, and I probably shouldn’t have put it in a glass jar, for a couple of reasons. The first is that it expands when it freezes, like water, so it could crack the jar. I wouldn’t want to have it spill — it’s both expensive and very messy. The second is that it sticks to glass, which means if you shake up the jar, it will coat the inside and you won’t be able to see in, unless you melt it again and scrape it off the sides somehow.

Gallium is not toxic like mercury; you can hold it in your hand, if you want to. But you probably don’t want to, since it sticks to everything, and leaves a powdery, gray residue on your hands. So it pours like mercury, but mercury doesn’t stick to glass like this and so is a lot cooler to pour or shake. I actually own some mercury, but I keep it sealed up in a jar inside a tin — because of its toxicity I don’t want to run the risk of a spill.

Another weird property of gallium is that it supercools. After you get it liquid, it takes forever to get it solid again. You can cool it far below its melting point — I had the jar lying sideways in the freezer — and it was very cold to the touch, but after an hour, some of it was still liquid. Very weird stuff. I’ll have to see if I can find a more suitable container for it — some kind of teflon-like plastic that it won’t stick to would be nice, but it would also be nice if it were transparent. I’m not sure there’s a plastic that meets both those requirements. I should ask Theodore Gray.

2022 followup: I did ask him. He said that didn’t know of any material that gallium wouldn’t stick to.

The jar is one of those tiny single-serving Heinz ketchup jars that you sometimes get in hotel room service meals. They’re useful for all kinds of things.

The next item is not really an element: it’s to illustrate the distinction between silicone and silicon. Silicon is an element; silicone is a whole family of compounds ranging from rubber-like materials to caulk to a dry-cleaning solvent. Silicone contains silicon. These are some of those awareness-raising rubber bracelets, in this case for breast cancer, which killed my mother in 2008.

Finally, this is a sample of calcium, which as you can see in its pure state is a metal. It oxidizes (and produces a nitride) giving itself a gray/black coating rapidly in air, especially humid air, so this sample is submerged in mineral oil, in another little glass jar wrapped with tape.

It was very blackened when I got it, which kind of ruined the effect — the whole point was that it should look like a shiny metal, because we don’t think of calcium that way. So I took it out of the oil and polished it up with a piece of emery paper, removing all the oxidation I could easily take off without sanding away too much of my sample. It’s not dangerously explosive or inflammable like sodium, although it oxidizes quickly enough that if you left the dry metal out for — I don’t know, maybe an hour or two, maybe a day or two — it would be completely gray/black with oxidation again.

Will it stay shiny in the oil indefinitely, or does oil hold dissolved oxygen that will oxidize it, just more slowly? I must confess I have no idea. I think for a really bright shiny sample you need to get a freshly cut and polished piece that is ampouled under argon gas.

That’s all for this round. The packages have slowed down to a trickle! There are still a few more coming, though, most notably the iodine, silicon, and the gas discharge tubes and apparatus (that should make some nifty photos!)

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