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Author: Subject: How to discover if something is made of Magnesium?
PyroPlatinum
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[*] posted on 22-1-2019 at 22:48
How to discover if something is made of Magnesium?


Hello guys.
I've searched the forum for a while (found nothing) and trying some alternatives that some sites suggest, and i know it sounds like a dumb question, but, how do i discover if a metal is indeed Magnesium?
What are the bestest ways to find this out?
What reactions can i do to discover it? (Even destructively)
That's what i want to know.
(Oh and i'm sorry if i posted this in the wrong section)
Thanks and have a great day!

[Edited on 23-1-2019 by PyroPlatinum]
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Vomaturge
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[*] posted on 22-1-2019 at 23:10


To destructively test a large object: take the backside (blunt side) of a knife or a conveniently shaped piece of sheet metal (don't cut yourself), and scrape a corner of it against it until dust and little curly strips of metal come off. Then, put them on a piece of toilet paper and ignite it. If there's Mg involved, you should see a few shavings 'fizzle' and turn white (magnesium oxide), and a few other particles vaporize in tiny white fireballs. The fizzle type reaction is especially prominent if they are ignited by exposure to sparks from a ferrocerium rod.

Source: I've practiced lighting a fire using one of those ferrocerium and magnesium 'metal matches'

here is what the 'fizzle' combustion looks like with a lot of magnesium and a flammable substrate. Unfortunately you can't see any flashes there, but believe me-you'll know when you see them.

Of course, this test only works on pure elemental magnesium, and not any of its compounds. Also, check your sample with a magnet before you waste your time scraping and burning.

[Edited on 23-1-2019 by Vomaturge]




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PyroPlatinum
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[*] posted on 22-1-2019 at 23:34


Quote: Originally posted by Vomaturge  
To destructively test a large object: take the backside (blunt side) of a knife, and scrape a corner of it against it until dust and little curly strips of metal come off. Then, put them on a piece of toilet paper and ignite it. If there's Mg involved, you should see a few shavings 'fizzle' and turn white (magnesium oxide), and a few other particles vaporize in tiny white fireballs. The fizzle type reaction is especially prominent if they are ignited by exposure to sparks from a ferrocerium rod.

Source: I've practiced lighting a fire using one of those ferrocerium and magnesium 'metal matches'


Hmmmm that sounds simple enough. Nice to know that.
Thanks!
I've heard that if you put some drops of vinegar (acetic acid) on it, it will begin to fizz. But i never tried that. I would like to know what reaction would be taking place that make it fizz.
Anyways. I've heard about a silver nitrate method too that if you are in doubt that a metal is aluminum or magnesium you put some drops of a silver nitrate solution on it, and if it leave a black precipitate (silver?) it is magnesium and if it is aluminum it will not react. But i never confirmed the veracity of this one too because i have no silver nitrate at the moment.

[Edited on 23-1-2019 by PyroPlatinum]
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Metacelsus
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[*] posted on 22-1-2019 at 23:53


Quote: Originally posted by PyroPlatinum  

I've heard that if you put some drops of vinegar (acetic acid) on it, it will begin to fizz. But i never tried that. I would like to know what reaction would be taking place that make it fizz.


Mg + 2 H+ -> Mg2+ + H2

Many other metals will also form hydrogen, so this test isn't very specific.

[Edited on 2019-1-23 by Metacelsus]




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PyroPlatinum
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[*] posted on 22-1-2019 at 23:59


Quote: Originally posted by Metacelsus  
Quote: Originally posted by PyroPlatinum  

I've heard that if you put some drops of vinegar (acetic acid) on it, it will begin to fizz. But i never tried that. I would like to know what reaction would be taking place that make it fizz.


Mg + 2 H+ -> Mg2+ + H2

Many other metals will also form hydrogen, so this test isn't very specific.

[Edited on 2019-1-23 by Metacelsus]


Hmmm... I was suspecting that it was Hydrogen.
Yeah, i would like to know a more distinct form of discovering it.
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[*] posted on 23-1-2019 at 07:05


Many other metals will also form silver, so that test isn't conclusive either. I guess it's supposed to work based on aluminum having a protective oxide layer while magnesium doesn't.

If it's a geometric shape or small enough to use water displacement, calculating density is another option.
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Morgan
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[*] posted on 23-1-2019 at 07:16


I remember cleaning the surface of a chunk magnesium firstarter and putting it in a flask with methanol. A little gentle heating and the metal started to fizz profusely. The very fluid remains would have easily clogged a drain, for the reaction with water forms a gel of amazing proportions.
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[*] posted on 23-1-2019 at 07:49


Testing with acid and burning are not definitive tests.

If you use an acid to dissolve some into solution, the following link gives some instruction on how you can test for ions present. Mg2+ is later in the video.

https://www.youtube.com/watch?v=RK1gdK7MHy0
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Fulmen
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[*] posted on 23-1-2019 at 10:29


The silver nitrate test works fine, I've tried it a number of times. It is fairly specific to pure Mg, none of the common alloys should react.

Other than that or the burn test? The density should be a dead give-away.




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[*] posted on 23-1-2019 at 12:24


I'm surprised the silver nitrate test is so specific. Why wouldn't it react with alloys? Surely the alloying elements are still more active than silver?
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Fulmen
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[*] posted on 23-1-2019 at 14:18


Idunno, but it works. Pure Mg always turned black while neither AM50/60 or AZ61/91 reacted. I suspect the aluminium oxide surface coating prevents the reaction.



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[*] posted on 23-1-2019 at 14:39


I used to know someone who worked in a scrap yard. I watched him sort a load of scrap one time. If they couldn't tell by sight they would shove it in a bench grinder and watch the sparks (or lack thereof) to determine the composition. I guess if you do it day in and day out you get an eye for it but it would be pretty subjective without training.



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[*] posted on 23-1-2019 at 20:27


Quote: Originally posted by BromicAcid  
I used to know someone who worked in a scrap yard. I watched him sort a load of scrap one time. If they couldn't tell by sight they would shove it in a bench grinder and watch the sparks (or lack thereof) to determine the composition. I guess if you do it day in and day out you get an eye for it but it would be pretty subjective without training.


The grinding test is the classic way for roughly determining the carbon content of steel. It's quite instructive to compare the spark patterns of mild steel versus those from pieces of known tool steel. And cast iron has a different pattern to all the others. This is very handy for blacksmiths who use odd bits of steel from scrap yards.

It would never have occurred to me, though, to test magnesium that way. I wonder if it is possible to accidentally ignite a smallish sample of Mg in this way. That would be one spectacular test if it did ignite!
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[*] posted on 24-1-2019 at 08:58


Not sure, I have ground Mg with a belt sander and that did not ignite. This was a setup using a water washer to "defuse" the dust, without it one spark would have made for a very bright death.



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[*] posted on 25-1-2019 at 07:31


For a quick non analytic test for magnesium test with magnet, Mg has little to no attraction to strong magnet. Secondly, skratch the oxide layer magnesium is very shiny, thirdly drip a tiny amount of vinegar on the suspected magnesium it will react were as 5% acetic acid doesn't react with aluminum, stainless, etc. This is obviously not an difinitive test how ever along with a burn test and a spark test
1+2+3+4+5 probably = Mg yay
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[*] posted on 26-1-2019 at 05:45


If you have a large enough chunk of the metal you can test its density.
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[*] posted on 26-1-2019 at 09:02


There is a classic qualitative analysis wet chemistry test for Mg++. Look it up.



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[*] posted on 26-1-2019 at 09:12


But is the sample alloyed with other metals like Al?



Useful sites:
Balance Chemical Equation: http://www.webqc.org/balance.php
Molecular mass and elemental composition calculator: https://www.webqc.org/mmcalc.php
Solubility table: https://en.wikipedia.org/wiki/Solubility_table
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