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Regarding a question on another Stack Exchange site which identifies a weighted Lego brick to be some kind of metal, I wanted to know how to identify a metal, perhaps limited to household objects like scales or a bowl of water to measure volume.

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Sounds like you already know how to do it using Archimede's principle.. that sheen is a dead giveaway but unfortunately the name of the material is slipping my mind right now. –  user2963 Jan 24 '12 at 21:51
    
I was wrong, that finish is a chromate coating which can be applied to a number of materials. I'd say check for magnetism and try the density test. –  user2963 Jan 24 '12 at 22:03
    
InRe moving to chemestry.se: I'm inclinded to say that my answer below is a physical one as much as a chemical one. I can ask the Chemistry mods if you would like, but I know of few explicitly chemical tests one could run with stuff found around the typical home. –  dmckee May 24 '12 at 20:22
    
@dmckee: I don't mind. I know migrations to beta sites aren't done lightly. –  Ambo100 May 24 '12 at 20:27
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The operative question is: is this question off topic here? I don't think so, though on this site the scope of the question will be limited to physical tests (measurements of density or specific heat, or mass spectrometry, or so on). So I think it'd be worth asking this question again on Chemistry to get another answer which will tell you about chemical tests you could do. –  David Z May 24 '12 at 20:41
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1 Answer 1

up vote 5 down vote accepted
  • Your big problem is that metallic alloys are so numerous that it very hard to do in general.

  • Your big advantage is that people mostly use things that are common, easy to get and cheap.

    This is especially true for something as mundane as a weight. Who's going to spend a lot of money sourcing something unusual? (Special case answer, when you need a lot of weight in a small space you might pay for tungsten.)


If I was tackling the problem in general I'd start with a simple visual inspection and then check the two properties that zerphy suggests in a comment are (density and magnetic character), and possibly ductility. They are easy to check with tools you'll find around any lab (and indeed around many houses).

As often the surface can be coated (e.g. hot-dip galvanizing) you can try scratching of a bit with sandpaper to see if the bulk material is different from the surface material. Many metals can be distinguished by their color already if you have a clean and polished surface.

At this point you should be able to sort out iron, steel (may not be magnetic and may be denser than iron), copper, aluminum, silver, lead, gold, bronze and brass.

(Note that telling one steel from another beyond stainless versus high-carbon versus other is not easy outside of a materials laboratory.)

If you are still stumped consider slightly exotic things like pewter, nickel, cobalt-steal{#}, titanium{+}, tungsten{#}, platinum, electrum, zinc, tin, and magnesium. Many of these have useful properties like extreme surface hardness (so taking a steel file to the sample could be useful) or unusually high or low density (which you would already know). Tin has a very low melting point. Magnesium of course burns easily and brilliantly (to the point of posing a significant hazard).

I suppose might encounter copper-berylium, but I'm not sure what you'd use to ID it beyond it's distinctive appearance.

After than you may want to take it to an expert.


{#} I've seen men's jewelry made of this stuff in recent years. Very spiffy.
{+} Increasingly available in consumer products. The body and band of my watch are titanium: it feels as light as a toy.

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Made community wiki to encourage contribution of more easy observations. –  dmckee Jan 24 '12 at 22:40
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