pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
Mercury Brownian Motion Demo
I came across a brownian motion demo a little while ago. It was an evacuated borosillicate tube with a splodge of mercury and some glass beads at the
bottom. It claimed that if you heated it over a spirit burner, the mercury would boil, and since the mercury gas would be so dense, the glass beads
would become suspended in it and would fly around the tube randomly.
This seemed a bit far fetched, glass beads just flying around in a vacuum, but I was intrigued so i bought one.
I heated it, and the mercury boiled, agitating the glass beads. But they still stayed sitting there at the bottom of the tube. Some of it had clearly
boiled, cause I could see a mercury mirror forming at the colder end of the tube.
So does anyone know what I'm doing wrong? Anyone else seen/used one of these before? Are the mnufactuer's claims realistic, can such large particles
of solids be suspended in a gas?
Here's a video on youtube, from back before I had a bunsen and a retort stand and had to make do with the kitchen hob and my hand instead.
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Somewhat related to one of your questions:
http://www.youtube.com/watch?v=qi7lTeXZu0o&feature=chann...
In this case, the air inside the aluminum boat is less dense than the surrounding sulfur hexafluoride, and therefore causes buoyancy...
So, a first step might be to determine the density of your mercury vapour and estimate the density of the glass beads?
Doesn't seem like the safest demonstration, however... especially in an ill-equiped kitchen! Be sure to review the relevant safety information for
mercury. Also, be exercise extreme caution when heating closed systems.
[Edited on 5/24/09 by bfesser]
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
Ah, very interesting 
I'm off out right now but when I get home I'll try and estimate the density of the mercury vapour. I guess it would be volume of Hg*density of liquid
Hg/volume of the tube
|
|
|
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
The density of mercury vapours is only seven times greater than that of air, at least according to its MSDS data sheet (that would be about
8.4 mg/mL at RT). That is a lot for something in its gas phase, yet not higher than the density of glass (>2000 mg/mL). You would have to have a
really high pressure of Hg vapours in order to achieve a density higher than that. I hope that is not what is supposed to be done with that
tube or else it is quite a dangerous toy!
Bfesser, thanks for the interesting video.
[Edited on 24/5/2009 by Nicodem]
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
Quote: Originally posted by Nicodem  | The density of mercury vapours is only seven times greater than that of air, at least according to its MSDS data sheet (that would be about
8.4 mg/mL at RT). That is a lot for something in its gas phase, yet not higher than the density of glass (>2000 mg/mL). You would have to have a
really high pressure of Hg vapours in order to achieve a density higher than that. I hope that is not what is supposed to be done with that
tube or else it is quite a dangerous toy!
Bfesser, thanks for the interesting video.
[Edited on 24/5/2009 by Nicodem] |
Yup, I just looked up the density of glass and its about 2.5g/cm3 liquid mercury's 13.5
So that would mean the tube would need to be 18.5% Hg, and that would have to be completely boiled. Then the tube would explode from the pressure.
Then youd have mercury gas everywhere. And the mercury gas would burn your flesh. And the mercury would enter your bloodstream. Then you'd be as mad
as a hatter.
[Edited on 25-5-2009 by pHzero]
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Who is the manufacturer, by the way?
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
I got it from rapid electronics: http://www.rapidonline.com/Educational-Products/Science/Labo...
It says that its made by RVFM, but I think that's their own brand.
|
|
|
panziandi
Hazard to Others
Posts: 490
Registered: 3-10-2006
Location: UK
Member Is Offline
Mood: Bored
|
|
I quote from the website he obtained this from:
| Quote: |
A superb demonstration of kinetic theory of matter and Brownian motion of molecules.
* A tube filled with small glass beads and mercury under highly evacuated condition
* When heated on a spirit lamp, the mercury boils quickly due to the low pressure and violently imparts bombarding motion to the glass beads
* Simulates Brownian motion with the glass beads behaving as gas molecules contained in an enclosed vessel
* Easily observable with the naked eye |
I do not believe that the glass beads float in the mercury vapour. Rather I think its the fact that the liquid mercury is SO dense that when it begins
to boil it "sploshes" around throwing the relatively light glass beads around the inside of the tube and its the random "dancing" of the glass beads
that simulates Brownian motion. And nothing to do with the beads floating on the mercury vapours!
However had the glass beads been aerogel then yes you could float them on mercury vapour!
P.S. My god pHzero, please do these experiments outside with a propane welding torch! You have food out on the side, and I/m sure you removed the gas
hob and were burning the gas straight from the gas pipe! SERIOUSLY dangerous. I'd never use mercury inside it's vapours readily absorb into the porous
wall and linger for ages, not to mention doing similar to your brain  (I can
almost imagine a certain continental member of this forum screaming like a banshee whilst watching that video  - sorry Jor )
|
|
|
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
Hahaha yes I agree. Although encapsulated what do you think would happen if say, you didnt heat the ampoule evenly... or you did and suddenly you drop
it because it gets too hot to hold. And this sort of thing is beyond KITCHEN chemistry! No chemistry should be done in the kitchen, ESPECIALLY when
there is food out, but generally it is a big no-no. Unless you're making CH3COONa from baking soda and vinegar! And when was the last time you cleaned
your kitchen....
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
| Quote: Originally posted by panziandi | I quote from the website he obtained this from:
| Quote: |
A superb demonstration of kinetic theory of matter and Brownian motion of molecules.
* A tube filled with small glass beads and mercury under highly evacuated condition
* When heated on a spirit lamp, the mercury boils quickly due to the low pressure and violently imparts bombarding motion to the glass beads
* Simulates Brownian motion with the glass beads behaving as gas molecules contained in an enclosed vessel
* Easily observable with the naked eye |
I do not believe that the glass beads float in the mercury vapour. Rather I think its the fact that the liquid mercury is SO dense that when it begins
to boil it "sploshes" around throwing the relatively light glass beads around the inside of the tube and its the random "dancing" of the glass beads
that simulates Brownian motion. And nothing to do with the beads floating on the mercury vapours!
However had the glass beads been aerogel then yes you could float them on mercury vapour! |
Oww thats a bit boring  I wanted floaty glass
But nah they definitely aint aerogel - you can feel as you shake it that theyre the mass of normal glass.
| Quote: | | P.S. My god pHzero, please do these experiments outside with a propane welding torch! You have food out on the side, and I/m sure you removed the gas
hob and were burning the gas straight from the gas pipe! SERIOUSLY dangerous. I'd never use mercury inside it's vapours readily absorb into the porous
wall and linger for ages, not to mention doing similar to your brain (I can
almost imagine a certain continental member of this forum screaming like a banshee whilst watching that video - sorry Jor ) |
Haha yeah I do everything involving fire outside or in my bedroom now, but when I made that video I couldnt. I've got a bottle of butane and a bunsen
now though.
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Your idea is interesting, though.
What if hollow (evacuated, gas, or air filled) beads were used instead of the solid glass? If the beads were carefully blown to match the density of
the mercury vapor at such and such a pressure... anyone have the time/resources to try it out?
|
|
|
panziandi
Hazard to Others
Posts: 490
Registered: 3-10-2006
Location: UK
Member Is Offline
Mood: Bored
|
|
bfesser: that thought did cross my mind too, my main concern would be that the beads may have such thin walls that when the mercury is sploshing
around as it boils the glass "balloons" may break. But alas I have no time/resources to try it out.
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Don't they sell calibrated density plastic beads for some biochem application? Protien gradient goo or whatever they do...
If they're sufficiently impermiable to the mercury, perhaps they'd be suitable. If not, maybe coat them with a very thin layer of fluorocarbon lube.
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
| Quote: Originally posted by bfesser | Don't they sell calibrated density plastic beads for some biochem application? Protien gradient goo or whatever they do...
If they're sufficiently impermiable to the mercury, perhaps they'd be suitable. If not, maybe coat them with a very thin layer of fluorocarbon lube.
|
I think it'd have to be glass - Hg doesnt boil till about 300 degrees, don't most plastics melt or degrade at that temperature?
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
True. I don't know what I was thinking. Are there any suitable metals or ceramics that come to mind?
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
I was just reading about something called carbon nanofoam on wiki. Apparently it's got about 1% of the density of an aerogel, only a couple of times
the density of air. If you put that in a tube of mercury gas, it'd probably float on the top like a helium baloon.
Ah now there's an idea. Small, hollow beads of glass about 1mm wide or so, either evacuated or filled with hydrogen or helium?
|
|
|
panziandi
Hazard to Others
Posts: 490
Registered: 3-10-2006
Location: UK
Member Is Offline
Mood: Bored
|
|
They sell glass beads for coating with DNA/Protein and for cell lysis IIRC but not too sure about if they have a specific density. Also the fact the
tube is evacuated is likely so that the mercury can be boiled at a lower temperature, that website mentions a spirit burner is sufficient to heat the
tube, so likely the mercury boils below its normal bp at a temperature that would be easily and quickly obtained by a spirit burner.
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Wouldn't the goal be to match the density of the beads with the density of the mercury vapor for neutral buoyancy? Wouldn't it be best to have the
beads float randomly within (3D) rather than atop (2D) the Hg vapor? Of course, this would be finicky.
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
| Quote: Originally posted by bfesser | | Wouldn't the goal be to match the density of the beads with the density of the mercury vapor for neutral buoyancy? Wouldn't it be best to have the
beads float randomly within (3D) rather than atop (2D) the Hg vapor? Of course, this would be finicky. |
Yeah, sorry i was being unclear. I meant it would be possible to get them to float on top, so that presumably means you could make them the same
density
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Kinda makes me wonder if supercritical carbon dioxide would be a more attainable and less hazardous option--besides the obvious explosion hazard.
|
|
|
bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Kinda makes me wonder if supercritical carbon dioxide would be a more attainable and less hazardous option--besides the obvious explosion hazard.
|
|
|
pHzero
Hazard to Self
Posts: 89
Registered: 16-5-2009
Member Is Offline
Mood: Fully substituted
|
|
| Quote: Originally posted by bfesser | | Kinda makes me wonder if supercritical carbon dioxide would be a more attainable and less hazardous option--besides the obvious explosion hazard.
|
Hmm, possibly, but dont supercritical fluids look like liquids? The idea really is just for the wow-factor of a solid floating in a gas, right? If you
want brownian motion in a liquid, you can just shake up a snow globe xD
SF6 would be great - nontoxic, unreactive, dense. Xe's more of the same but a lot more expesnive
Hydrogen filled glass beads in SF6 maybe?
|
|
|
panziandi
Hazard to Others
Posts: 490
Registered: 3-10-2006
Location: UK
Member Is Offline
Mood: Bored
|
|
No. Supercritical fluids are more like gases. If you have a glass vessel with both liquid CO2 and gaseous CO2 - and you heat the vessel the meniscus
disappears. They behave as a cross between liquids and gases. Why didn't you opt for a snow globe? It would have been the safer option for your
food-laden kitchen
[Edited on 1-6-2009 by panziandi]
|
|
|
Endimion17
International Hazard
Posts: 1468
Registered: 17-7-2011
Location: shores of a solar sea
Member Is Offline
Mood: speeding through time at the rate of 1 second per second
|
|
Sorry for lifting an old thread, but I was looking for something about mercury (that's why I registered; btw hi everyone), and this came up in the
search.
After all, I'm not spamming, but offering a solution which never appeared in the discussion.
I've seen this experiment long time ago. It is possible, but there won't be any floating.
Here it is.
The key is to have light pieces of flat glass, so the heavy atoms of Hg will be able to bump into them and bounce them upwards.
The tube should be quartz, under vacuum, and you should work over a heat resistant bucket or something, and strong ventilation is a must. I'd put some
water in the bucket, too.
Just imagine the danger of tube cracking and hot, boiling metal splashing around.
I hope it helps.
BTW you should really check CHEM Study videos. I've seen those on Archive.org a long time ago, and now they are on Youtube, too.
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
That's an interesting video Endimion17, and I think this was what the original poster had in mind.
The correct construction of this demonstration device is obviously crucial for both safety and functionality.
First, the tube has to be evacuated since this prevents it from building overpressure when the upper walls of the long tube are colder than the
boiling point of mercury at atmospheric pressure. A wet cloth around the upper part of the tube should be sufficient cooling.
Also, it must be made of quartz due to the temperature gradients.
Secondly, I think that this special "brownian motion" effect in the video only works in a vacuum since only there the mercury atoms can move freely
enough and reach a high speed in the upwards direction.
Perhaps the effect has more to do with the high flow velocity of the gaseous mercury that is expanding into a vacuum and recondensing at the cold
upper part of the tube?
Kremer sells hollow glass beads under the name Scotchlite K1, which have a nominal density of 0,125 g/ml and an average size of 46 micrometers. These
aren't going to truly float on mercury vapor, but might be ideal for this demo if they don't burst from their inner pressure in a vacuum.
I wonder whether some light materials like styrofoam can be gotten to float on an extra heavy, not too hot gas like the vapors from boiling carbon
tetrachloride... if styrofoam were resistant towards CCl4 (which it isn't) then it could work! Perhaps seal it into very thin PE foil?
Another extra high density gas that comes to mind is perfluorohexane, C6F14.
http://en.wikipedia.org/wiki/Perfluorohexane
Molar mass far higher than SF6, low boiling point- seems like an ideal super-heavy gas (hey, even heavier than Radon!) when working at warm
temperatures. It has a steep price, but since you don't need a gas cylinder like for SF6 it might be the more economic choice for demonstrations.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
