Sciencemadness Discussion Board - Mercury Brownian Motion Demo

Mercury Brownian Motion Demo

pHzero - 24-5-2009 at 06:03

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 - 24-5-2009 at 10:32

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 - 24-5-2009 at 10:41

Quote: Originally posted by bfesser

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, maybe you could try to determine the density of your mercury vapour and estimate the density of the glass beads?

[Edited on 5/24/09 by bfesser]

[Edited on 5/24/09 by bfesser]

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 - 24-5-2009 at 10:44

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 - 24-5-2009 at 16:18

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 - 25-5-2009 at 07:46

Who is the manufacturer, by the way?

pHzero - 25-5-2009 at 07:53

Quote: Originally posted by bfesser

Who is the manufacturer, by the way?

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 - 25-5-2009 at 14:06

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 - 25-5-2009 at 14:11

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 - 25-5-2009 at 15:17

Quote: Originally posted by panziandi

I quote from the website he obtained this from:

Quote:

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 - 25-5-2009 at 18:44

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 - 26-5-2009 at 01:03

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 - 26-5-2009 at 11:23

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 - 26-5-2009 at 11:49

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 - 27-5-2009 at 05:30

True. I don't know what I was thinking. Are there any suitable metals or ceramics that come to mind?

pHzero - 27-5-2009 at 05:44

Quote: Originally posted by bfesser

True. I don't know what I was thinking. Are there any suitable metals or ceramics that come to mind?

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 - 27-5-2009 at 06:20

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 - 27-5-2009 at 12:33

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 - 27-5-2009 at 12:35

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 - 27-5-2009 at 13:11

Kinda makes me wonder if supercritical carbon dioxide would be a more attainable and less hazardous option--besides the obvious explosion hazard.

bfesser - 27-5-2009 at 13:13

Kinda makes me wonder if supercritical carbon dioxide would be a more attainable and less hazardous option--besides the obvious explosion hazard.

pHzero - 27-5-2009 at 13:23

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 - 1-6-2009 at 02:32

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 - 17-7-2011 at 08:20

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 - 25-7-2011 at 06:55

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.