tried (or at least observed). Breathing UF6 seems just so wrong at so
might not "couple" at all with such a heavy and odd element. I suppose
wicked. And all the hydrocarbons playing in there somewhere too I
> A really spectacular (and somewhat dangerous) demo involves what I
> would guess is the densest gas of all, uranium hexafloride, with a
> mass of 352 gm/mole. Remember that at equal temperature and pressure a
> mole of any gas whatsoever occupies a volume of 22.4 liters, so the
> grams/mole is proportional to the grams/liter.
>
> The demonstrator breathes in the UF6 and then talks with a very deep
> voice, the opposite effect to breathing in helium and talking with a
> very high voice. The explanation is that the vocal cavity dimensions
> don't change, so resonant wavelengths don't change. The speed of sound
> in a gas is similar to the average speed of molecules in the air,
> which is v = sqrt(3kT/m), where m is the mass of one molecule, k is
> Boltzmann's constant, and T is the absolute temperature. Therefore the
> speed of sound is much higher in helium than in air, and much lower in
> UF6 than in air. Since the speed of sound = wavelength/period =
> wavelength*frequency, the frequency of a resonance in the voice cavity
> is high in helium and low in UF6.
>
> In the helium case, it's easy to get rid of the helium and replace it
> with air because the helium has lower density than air. But to get rid
> of the UF6 the demonstrator has to lean over or stand upside down to
> spill the heavy gas out of the lungs. (Note: the radioactivity of
> ordinary uranium, which is 99.3% U238, or of "depleted" uranium from
> which the U235 has been removed, is quite low. U238 has a very long
> half-life of 4.4 billion years, so the number of decays per second in
> the UF6 is low. The danger in breathing in UF6 is from lack of oxygen,
> not from radioactivity.)
>
> In an atmosphere with approximately constant absolute temperature and
> no convection, the density of a particular gas is proportional to e
> raised to the power (-mgy/kT), where m is the mass of one molecule in
> kilograms, g is 9.8 N/kg (gravitational field strength), y is the
> height above the ground in meters, k is Boltzmann's constant in
> joules/kelvin, and T is the absolute temperature in kelvins. For
> oxygen, at a height y = 7920 meters (roughly the height of Mt.
> Everest), (-mgy/kT) = 1, so the density is down by a factor of e to
> the -1, which is 0.37. In other words, in this simplified model the
> density of oxygen at the top of Everest is about one-third what it is
> at sea level. (Note that some climbers have made it to the top
> breathing only what air was available there.)
>
> The corresponding "mean heights" for various gases in this model:
>
> oxygen 7920 m
> nitrogen 9050 m
> CO2 5500 m
> helium 63400 m (way above almost all of our atmosphere)
> UF6 720 m
>
> Note that the mean heights for oxygen and nitrogen aren't very
> different, so one can expect mixing to destroy any significant
> separation. On the other hand, one can expect helium to escape from
> the Earth, and it does, and one can expect some significant pooling of
> UF6 when you pour it out onto the floor.
>
> Bruce
>
> On Tue, Jun 12, 2012 at 12:33 PM, Roger Critchlow<
[hidden email]> wrote:
>> Nick --
>>
>> N2 weighs 28 gm/mole, O2 weighs 32 gm/mole, Ar weighs 40 gm/mole, CO2 weighs
>> 44 gm/mole, and H2O weighs 18 gm/mole.
>>
>> Why would anyone expect the lighter components of a mixture to fall down
>> more than the heavier ones? If anything, you'd expect the heavier ones to
>> concentrate toward the bottom.
>>
>> And why would anyone expect a mixture to spontaneously separate into pure
>> components? That happens in real life like where?
>>
>> As it happens, CO2 is the heaviest normal component and it does pool in
>> confined spaces often enough that CO2 alarms are available in hardware
>> stores. Propane, C3H8, weighs 44 gm/mole and is notorious for pooling in
>> confined spaces and then exploding, often in the bilge of a boat and
>> spectacularly.
>>
>> -- rec --
>>
>> On Tue, Jun 12, 2012 at 10:44 AM, Nicholas Thompson
>> <
[hidden email]> wrote:
>>> So, somebody asked me, in my role as a weather nerd, how come the nitrogen
>>> in the atmosphere doesn’t all fall to the bottom on still nights and
>>> suffocate us all. I asked the question of
>>> stupid-answers-to-stupid-questions-asked-by-stupid-people.com and THEY said,
>>> well, there’s just too much going on. N molecules and the O molecules are
>>> just too busy, what with convection and windcurrents, and all, to separate,
>>> even on still nights. Now, that business doesn’t prevent cold molecules of
>>> Nitrogen and Oxygen to separate from warm ones, or wet ones (not sure what
>>> that means) to separate from dry ones. I was hoping that somebody on FRIAM
>>> could give some sort of a clue what kind of a mixture AIR is? It is
>>> suddenly seeming kinda special.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Nicholas S. Thompson
>>>
>>> Emeritus Professor of Psychology and Biology
>>>
>>> Clark University
>>>
>>>
http://home.earthlink.net/~nickthompson/naturaldesigns/>>>
>>>
http://www.cusf.org>>>
>>>
>>>
>>>
>>>
>>>
>>> ============================================================
>>> FRIAM Applied Complexity Group listserv
>>> Meets Fridays 9a-11:30 at cafe at St. John's College
>>> lectures, archives, unsubscribe, maps at
http://www.friam.org>>
>>
>> ============================================================
>> FRIAM Applied Complexity Group listserv
>> Meets Fridays 9a-11:30 at cafe at St. John's College
>> lectures, archives, unsubscribe, maps at
http://www.friam.org> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9a-11:30 at cafe at St. John's College
> lectures, archives, unsubscribe, maps at
http://www.friam.org>
Meets Fridays 9a-11:30 at cafe at St. John's College