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Author: Subject: Identification of a mystery metal
opfromthestart
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[*] posted on 2-5-2019 at 03:39


The density was calculated by my teacher when she received the sample. I was incorrect when I said that she recieved it with that label.
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opfromthestart
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[*] posted on 2-5-2019 at 03:52


Quote: Originally posted by ScienceHideout  


Also, looking at the bottle, it is probably a single metal and not an alloy. It has an analysis on it that says 100.0%...

[Edited on 2-5-2019 by ScienceHideout]


I hadn't noticed that. However, as elementcollector1 said, the only pure metal with that density is terbium, which is the first thing I tested it for. Since it did not react I suspect it is not a pure metal.
Also, the container itself may be not specific to the metal and may have been intended for something else, if that is a possibility.
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opfromthestart
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[*] posted on 2-5-2019 at 06:44


I heated some scrapings of the metal in a crucible with a Bunsen burner. It didn't appear to melt but quickly oxidized when I held the inner blue cone of the flame. It oxidized into a black solid.

I will try dissolving the solid in nitric and hydrochloric acid to see if it has any distinctive metal ion colors.
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[*] posted on 2-5-2019 at 06:51


Small pieces of scrapings would probably completely oxidize before they could melt. Try larger pieces.

[Edited on 190502 by fusso]




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elementcollector1
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[*] posted on 2-5-2019 at 17:06


Assuming that black isn't soot, it's a good start. Metals with black oxides, according to the list, are:

-Chromium (II) oxide. Very unlikely owing to the nature of its existence.
-Chromium (IV) oxide. Also unlikely.
-Cobalt oxide. Hardness of the metal is entirely wrong for cobalt.
-Iron (II) oxide. Hardness is wrong, same as cobalt.
-Iron (II, III) oxide - magnetite. See above.
-Copper(II) oxide. Color is wrong.
-Lead (IV) oxide. Now this is a possible candidate.
-Manganese (IV) oxide. See cobalt and iron.
-Silver (I) oxide. I might almost believe this one, honestly. Pure silver is more dense than the sample, but alloyed silver is still on the table.
-Tin (II) oxide. Apparently it's flammable, burning to tin (IV) oxide, so if the black color remained after burning for a while it's probably not this.

Of those, the two best candidates are lead and silver, and my money's definitely on lead, alloyed with something lighter like tin.

[Edited on 5/3/2019 by elementcollector1]




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[*] posted on 2-5-2019 at 20:22


Quote: Originally posted by opfromthestart  
The density was calculated by my teacher when she received the sample. I was incorrect when I said that she recieved it with that label.


I understand, but...

1. We are dealing with a pure metal, according to the analysis.

2. The only metal with a density close to that is terbium.

3. It was determined that said metal is not terbium.

So something is wrong: it is either the label, the density, or the confirmation of not-terbium.

Unless the bottle was recycled (unlikely), the analysis is probably correct. You tested for terbium and got a negative result, which I believe for several reasons.

Density, on the other hand...

We are all human. Your AP chemistry teacher is, too. She may have made a mistake while determining the density. This is why analysts often do measurements in triplicate when applicable. This is not to say she is stupid, just that accidents happen! In situations like this in particular, an experimental blunder could go unnoticed because it wouldn't propagate a big, blatant, questionable error: Something as simple as forgetting to tare the balance, or pressing the wrong button on the calculator could have given her the wrong density, and we have no way of knowing since it was measured only once.

It doesn't take very long to put a piece on a scale, and then submerge it in water. Sure, you might find that your teacher's analysis was correct, and you still cannot confirm the identity. BUT, there is also a chance that you come up with a different number, and those couple minutes of double checking could provide a definite answer. If you have time to play around with corrosive acids and fire, you have time to do this. :P

TL;DR- It pays to double check. Take another density measurement to assure that your teacher didn't overlook a simple mistake. It only takes a few seconds.




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Fulmen
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[*] posted on 3-5-2019 at 05:11


Quote: Originally posted by ScienceHideout  
Unless the bottle was recycled (unlikely)

What lead you to that conclusion?

[Edited on 3-5-19 by Fulmen]




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opfromthestart
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[*] posted on 3-5-2019 at 08:11


She just tested the densities of two of the samples and they came back as 6.407 g/cm^3 and 7.337 g/cm^3. Since this disparity seems too great to be due to measurement error and I did the calculations myself(and checked it), I believe the samples may be different metals or at least different compositions of a similar alloy. One of my classmates will be testing the other 4 samples later today.



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[*] posted on 3-5-2019 at 12:13


Those are either solder bars/sticks for making stained glass windows or babbitt in extruded wire form
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[*] posted on 3-5-2019 at 13:20


Fulmen, I don't believe that bottle was recycled because I have seen metal sticks packaged in that type of bottle before. So unless someone took some sticks out, and put others in, I doubt it was recycled.

Opfromthestart, That is certainly interesting. I'd be willing to bet that they all are the same metal: I don't see why there would be different ones in the same bottle that look the same, and again, unlikely that there are various alloy compositions due to "100%" being on the bottle. That being said, both 6.407, 7.337, and 8.19 are all very different measurements. I am really looking forward to the results from your classmates- this could provide one single accurate measurement. Out of curiosity, have you guys ever tried either a pycnometric method, or hydrostatic weighing? These could both help improve your density measurements by omitting the need for volume measurement.

OldNubbins, They do certainly look like that! Does stained glass solder normally come in a bottle like that, though? What is the typical melting point of stained glass solder?

[Edited on 3-5-2019 by ScienceHideout]




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[*] posted on 3-5-2019 at 15:30


Regular 50/50 or 60/40 solder (no rosin core) is used, nothing special. Melting point around 400°. Comes in various sizes depending on the application. i have seen bars larger then the OP's. You can tell the OP's material is extruded because of the seams on the sides and tapered ends. There's no way to know if the paper tube in the OP's picture is the original package - wouldn't really help anyways since it can come in anything or nothing.
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[*] posted on 3-5-2019 at 17:57


Quote: Originally posted by OldNubbins  
You can tell the OP's material is extruded because of the seams on the sides and tapered ends.


Is this why you believe it's solder, though? I mean, a lot of metals are extruded...




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[*] posted on 3-5-2019 at 19:01


Quote: Originally posted by ScienceHideout  

Is this why you believe it's solder, though? I mean, a lot of metals are extruded...


True, but that plus other evidence is increasingly leaning towards solder or something similar. For reference, a eutectic lead/tin solder alloy (63% Sn, 37% Pb) has a density of approximately 8.4 g/cc.

Still, chemical tests will likely tell us something more. OP could also differentiate between silver-based and lead-based by checking if the bulk metal melts on stovetop heat (though if it's lead, might want to turn the vent fan up. Or use a hotplate in a fume hood).




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[*] posted on 3-5-2019 at 21:53


Quote: Originally posted by ScienceHideout  
Quote: Originally posted by OldNubbins  
You can tell the OP's material is extruded because of the seams on the sides and tapered ends.


Is this why you believe it's solder, though? I mean, a lot of metals are extruded...


The extrusion marks are only one of the examples I gave. I am convinced it is solder or some other low melt alloy. You don't have to be, you are welcome to investigate further, unfortunately with the limited amount of information the OP has given, we are at an impasse.
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[*] posted on 3-5-2019 at 21:59


Quote: Originally posted by elementcollector1  
Quote: Originally posted by ScienceHideout  

Is this why you believe it's solder, though? I mean, a lot of metals are extruded...


True, but that plus other evidence is increasingly leaning towards solder or something similar. For reference, a eutectic lead/tin solder alloy (63% Sn, 37% Pb) has a density of approximately 8.4 g/cc.

Still, chemical tests will likely tell us something more. OP could also differentiate between silver-based and lead-based by checking if the bulk metal melts on stovetop heat (though if it's lead, might want to turn the vent fan up. Or use a hotplate in a fume hood).


One way I check for lead is to melt the alloy (solder, babbitt, other low-melts) in question, throw some KNO3 into the melt and give it a mix. Yellowish litharge should form (PbO), Bob's your uncle!
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[*] posted on 4-5-2019 at 00:19


Quote: Originally posted by OldNubbins  
You can tell the OP's material is extruded because of the seams on the sides and tapered ends


I disagree. The seams looks more like mould lines, extruded bars will typically have fine axial lines around the entire perimeter. The surface also has wrinkles that looks more like cast (or perhaps even stamped) metal.
And just to be clear, not only have I seen cast and extruded lead before, I've even made it and the tooling myself.

Most of the ends aren't really tapered, they look more like they've been cut with bolt cutters. The tapering could be from use if it's solder.




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[*] posted on 4-5-2019 at 12:26


I remember a thread where someone found a mystery metal rod, which turned out to be actual platinum. (185 grams of it!)

Found it: https://www.sciencemadness.org/whisper/viewthread.php?tid=20...

[Edited on 4-5-2019 by phlogiston]




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[*] posted on 4-5-2019 at 13:08


Quote: Originally posted by phlogiston  
I remember a thread where someone found a mystery metal rod, which turned out to be actual platinum. (185 grams of it!)

Found it: https://www.sciencemadness.org/whisper/viewthread.php?tid=20...

[Edited on 4-5-2019 by phlogiston]


I read the thread, apparently there wasn't any real conclusion was there?

Regarding the mystery metal in this thread, those look like extruded metal rods, cut with a hydraulic shear. When you cut thick wire you the same pattern on the cut end. That narrows it to softer metals that can be extruded that way. I have a bar of cadmium that looks similar, different density though.
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[*] posted on 4-5-2019 at 13:51


Quote: Originally posted by opfromthestart  
She just tested the densities of two of the samples and they came back as 6.407 g/cm^3 and 7.337 g/cm^3.

ALARM !
... those are very precise numbers,
and different from each other and the original sample.

The test of density is surprisingly quick, easy and accurate.
It does not rely on the accuracy of the only instrument required, the scales,
it only relies on their linearity - for a weight ratio.

The crud will need to be mechanically removed from each stick
(keep the crud from each, separately, until you KNOW that it is worthless)
and, any tiny bubbles on the submerged surface will give significant errors.
I have used this method many times, and cross-checked by other means, 1% accuracy is easily attainable using cheap scales.
(Correction must of course be made for the variation of the density of water with temperature if accurate results are required.)

If there are three of you then each of you should measure all samples - then compare notes.
(using your teacher's results) as a reference - with an open objective mind)
Simple techniques are worth mastering - for confidence in your own abilities.
PLUS
it would enable more concise and precise discussions with other members.

P.S. I was refering to this type of measurement https://www.youtube.com/watch?v=xYdSEAm-7uI
https://www.youtube.com/watch?v=N1HCrNMnb9I

[Edited on 4-5-2019 by Sulaiman]




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opfromthestart
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[*] posted on 6-5-2019 at 05:12


The samples were tested with an analytical balance(the fancy one with doors, i think about .001g accuracy).

The samples tested around 7.3 but some were as high as 7.6(each was tested 3 times by both the teacher and my classmate, I wasnt there).

When my teacher removed most of the oxidation, the density dropped to 7.06. This sets the pure metal possibilities to Mn, Cr, and In, and possibly a few I overlooked.




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[*] posted on 6-5-2019 at 05:20


The few metal oxides that are denser than the metal are some alkali, earth & RE metals...

[Edited on 190506 by fusso]




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[*] posted on 6-5-2019 at 06:55


Quote: Originally posted by fusso  
The few metal oxides that are denser than the metal are some alkali, earth & RE metals...

[Edited on 190506 by fusso]


Well, it doesn't react with acid or water so i doubt its any of those.




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[*] posted on 6-5-2019 at 07:52


Most earth sulphates are insoluble so it may form some protective layer in H2SO4?



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[*] posted on 6-5-2019 at 08:00


If it would be a RE metal, it would probably have to be Ce, Pr, or Yb based on the density.



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[*] posted on 6-5-2019 at 08:15


Cerium and Ytterbium oxide are not black, and Praseodymium is paramagnetic, which the rods are not. So... still probably an alloy.



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