invisible water effect

[the guy]

cool take a look at this video:

http://uk.youtube.com/watch?v=tAsOfqCy4A0

cool isn't it?

is it just as simple as sulfur hexaflouride in a tank and a foil boat or is there more to it? If you put that stuff in a glass container with glitter in would it do the same thing as those snow storm souvenir ornament things with the man in which you shake?

[YT2095]

Aerogel "glitter" might work.

[the guy]

what's aerogel glitter?

[YT2095]

bits of Aerogel made shiny I guess.

expanded polystyrene might work also.

[swansont]

 

is it just as simple as sulfur hexaflouride in a tank and a foil boat or is there more to it?

 

No, that's all there is.

[hermanntrude]

i've been researching this stuff and i'd really like to use it in my lab for demos. the trouble is that it costs $300 for a small cylinder (lecture bottle). I'm not sure i can justify the cost

[YT2095]

couldn`t you sell Tickets and/or get a subsidy from your School?

[hermanntrude]

i wouldnt sell tickets because i'm an instructor, not a circus performer. And it'd be the school that paid for the whole thing... however, it seems like a lot of money for one demo, and i dont know if i can justify the cost to my seniors

[DrP]

OK - just watched the video without sound - so don't know how it's done. don't know alot about sulfur hexaflouride - I presume it's really dense. What about a heavy noble gas like Argon or Xenon? Would that work?

[Gilded]

OK - just watched the video without sound - so don't know how it's done. don't know alot about sulfur hexaflouride - I presume it's really dense. What about a heavy noble gas like Argon or Xenon? Would that work?

 

Argon isn't really dense at all. But SF6 has a density of 6.164 g/L and xenon has a density of 5.894 g/L. So it's doable with xenon, but I'm not sure if it's any less expensive than SF6.

[jdurg]

True, but I don't think the Xenon would have all the regulations associated with it as SF6 does due to it being a very potent greenhouse gas.

[Comandante]

to extend into this thread; is it possible to make a gas so that it's dense enough to be able to slow human fall through it, something like swimming in the water but swimming in the gas instead, just like the boat on sulfur hexafluoride? I can imagine that being very hard and my guess would be a no, but that's why I'm asking..

[Gilded]

to extend into this thread; is it possible to make a gas so that it's dense enough to be able to slow human fall through it, something like swimming in the water but swimming in the gas instead, just like the boat on sulfur hexafluoride? I can imagine that being very hard and my guess would be a no, but that's why I'm asking..

 

Seems like tungsten hexafluoride is pretty much as dense as a gas can be at STP, and it has a density of 13.1g/L vs. water's ~1kg/L. While an object will fall much slower through such a gas than it would through air the density would have to be dozens of times higher for swimming.

[npts2020]

You could probaby (in theory) pressurize any gas to be thick enough to swim in if you had some way of surviving the pressure.

[John Cuthber]

You could probaby (in theory) pressurize any gas to be thick enough to swim in if you had some way of surviving the pressure.

Probably not.

Some gases perhaps but not just any gas. Air is roughly a thousand times less dense than water so, by boyle's law you would need about 1000 bar pressure to get it as dense as water. However the critical pressures of oxygen and nitrogen are much lower than that so you wouldn't be swimining in a gas, but in a supercritical fluid (assuming it didn't do anything silly like solidify).

[Klaynos]

I suspect anything that dense at STP will have gone through a phase change from a gas into something else...

[npts2020]

Probably not.

Some gases perhaps but not just any gas. Air is roughly a thousand times less dense than water so, by boyle's law you would need about 1000 bar pressure to get it as dense as water. However the critical pressures of oxygen and nitrogen are much lower than that so you wouldn't be swimining in a gas, but in a supercritical fluid (assuming it didn't do anything silly like solidify).

 

True. I wasn't thinking about phase change under pressure. Would you accept me specifying any gas that didn't undergo phase change? Or are you saying that all gases would phase change before reaching sufficient density?

[Comandante]

hmmm, maybe there is a way to do it.

 

Speaking broadly, assuming that increasing the pressure increases the density and therefore the proximity of molecules in a gas, what if one was to use a gas of molecules that repelled each other due to external influence (maybe electrical stimuli or something along those lines) so that the phase change into liquid or other would be more difficult to happen and so greater density achieved with the given gas compound? I imagine that would require greater external pressure too to achieve the required density... but would it work?

[hermanntrude]

perhaps a plasma (which acts a bit like a gas) could get that dense

[jdurg]

perhaps a plasma (which acts a bit like a gas) could get that dense

 

Yes. Take a look at the sun or any other star out there. They are very dense and also very hot. Therefore, walking in there wouldn't be all that possible.

[npts2020]

Well you can't really walk on water either. My guess would be that you wouldn't sink to the center of the sun, until you were vaporized and some of the heaviest atoms in your body arrived there, as some strata before the center seems likely to be where you would be neutrally bouyant. I don't think anyone has really answered if any gas could possibly be bouyant enough to float a human, it seems probably not.

[the guy]

i know i am bringing this up after a very long time but going back to my question about the glitter, would very fine powder sink slowly in it as if it were water, like flour or something?

Edited October 3, 2010 by the guy

[the guy]

also, it says on wikipedia that

'In Europe, SF6 falls under the F-Gas directive which ban or control its usage for several applications. Since 1 January 2006, SF6 is banned as a tracer gas and in all applications except high voltage switchgear'.

 

1. does this mean just that all the other applications have been banned or that it is actually not allowed to be used for anything except switchgear, even if a new application came up?

 

2. does it mean that you can't buy it in canisters or use it for demonstrations?

 

oh and one more thing,

i've been researching this stuff and i'd really like to use it in my lab for demos. the trouble is that it costs $300 for a small cylinder (lecture bottle). I'm not sure i can justify the cost

 

why is it so expensive? i looked at how it is made and it is not a very complicated method, and as far as i'm aware sulfur and fluorine aren't that expensive either...