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Sulaiman

Tue Apr 25 2017, 10:33AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Physikfan wrote ...

Hi Sulaiman

Please, could you show me the link to
"After watching the Cody's Lab video"

Do you have the possibility to do such experiments outdoors or in a glovebox?
As you may know, very small, almost invisible mercury globules can spoil the air in a closed room for years.
As a teenager I once had a mercury poisoning through a broken fever thermometer in the bedroom.

The second link in my first post on this topic, above.

Most experiments like this I do in my alfresco laboratory, recently relocated and repainted.

I doubt that you had significant mercury poisoning due to the vapour from the liquid mercury of one thermometer,
unless you sleep on the floor,
the vapour pressure is so low that mercury evaporates very slowly,
even a little ventilation (opening the door twice a day) should make mercury vapour concentrations negligible.
Were you clinically diagnosed using blood tests ?
(very often chemical exposure can cause psychosomatic symptoms)

If you do have a small mercury spill, use powdered sulphur.
......................................... .................................
"The limiting factor of such pumps is the vapor pressure of the liquid media.
Normal vacuum pump oil about 10 ** - 3 mbar
Mercury at 20 Â° C also about 10 ** -3 mbar"
................................................. .........................
True, but rotary pumps do not get down to the vapour pressure of the oil due to mechanical limitations,
and oil instead of mercury for a Sprengel pump would require a very long drop (c11m) due to the difference in density.

Proud Mary

Tue Apr 25 2017, 03:08PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Mr Physik,

have you heard of The Bell Jar : Vacuum Techniques and Related Topics for the Amateur Investigator?

It is full of good stuff, some of it dating back more than 50 years.

johnf

Tue Apr 25 2017, 07:31PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Heres the link to home made tubes
i'm sure the toepler pump is in there somewhere

jpsmith123

Tue Apr 25 2017, 07:41PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Speaking of the Bell Jar, this article may be of interest:

On my mechanical vacuum pump, I use two traps in series; a shredded copper trap to block back-streaming pump oil, followed by a molecular sieve trap, which will trap both oil vapor and water vapor. I also have some Edwards "Ultragrade 19" mechanical pump oil which is supposed to have a relatively low vapor pressure.

I'm not sure how low this system will go, but it rapidly buries my Varian 531 TC gauge; so I think it's well below 0.001 torr.

Physikfan

Tue Apr 25 2017, 08:15PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Sulaiman

I have read about the Sprengel pump in Wikipedia, the free encyclopedia.
"The device was later found capable of reducing the pressure to less than 1 mPa (9.87 x10âˆ’9 atm).[5]"
This source [5] is "The New Student's Reference Work/Air Pump"
with the following statement without a further reference:
"A pump of this type is capable of producing a vacuum in which the pressure is only 100,000,000th of an atmosphere."
I cannot believe that a mercury filled Sprengel pump could produce a pressure which is lower by a factor of 100 than the vapor pressure of mercury itself.

Please I am looking forward to all your comments.

Physikfan

Tue Apr 25 2017, 08:29PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Ad my mercury poisoning as a teenager:
I slept very close to mercury droplets inside a carpet during weeks.
As a consequence I had several times a very large increased salivation which is a typical phenomenon for a mercury poisoning.

Sulaiman

Tue Apr 25 2017, 11:49PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Physikfan wrote ...

"A pump of this type is capable of producing a vacuum in which the pressure is only 100,000,000th of an atmosphere."
I cannot believe that a mercury filled Sprengel pump could produce a pressure which is lower by a factor of 100 than the vapor pressure of mercury itself.

Please I am looking forward to all your comments.

Although the vapour pressure of mercury at room temperature is about 1 Pa
it is about 0.1 Pa at 0C and the triple point of mercury is -39 C, 0.2 mPa
and 1/100,000,000 atmosphere = 1 mPa
... seems achievable, but not easy.

Physikfan

Wed Apr 26 2017, 12:53PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

I have used a vapor pressure calculator

to compute a few vapor pressure values for Hg and Ga:

Hg:

T(K)___T(Â°C)_p(mbar)
233.2 - 40.00
238.2 -35.00 5.33e-6
243.2 -30.00 1.01e- 5
248.2 -25.00 1.85e-5
253.2 -20.00 3.31e- 5
258.1 -15.00 5.81e-5
263.1 -10.00 9.98e- 5
268.1 -5.000 1.68e-4
273.1 0.000 2.77e- 4
278.1 5.000 4.50e-4
283.1 10.00 7.17e- 4
288.1 15.00 1.12e-3
293.1 20.00 1.74e- 3
298.1 25.00 2.64e-3
303.1 30.00 3.97e- 3
308.1 35.00 5.88e-3
313.1 40.00 8.61e- 3
318.1 45.00 0.0124
323.1 50.00 0.0178

Ga:

T(K) __T(Â°C)__p(mbar)
303.1 30.00 6.08e- 38
308.1 35.00 3.39e-37
313.1 40.00 1.79e- 36
318.1 45.00 8.94e-36
323.1 50.00 4.26e-35

At the moment the vapor pressure values for gallium seem to me extremely low, even uncredibly low.
I will try to find real scientific papers on vapor pressures of liquid gallium to verify these numbers above.
For 100 g gallium I found prices around 50 Euro at ebay.

The question is:
How much liquid gallium is necessary to realise a Sprengel pump with liquid gallium at 40Â°C?

Physikfan

Wed Apr 26 2017, 01:33PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Here are another sources for the vapor pressure of gallium:

"This very efficient cooling and the very low vapor pressure for
liquid gallium (less than 10**-12 Torr at 100Â°C) make liquid gallium a very
attractive cooling fluid for high vacuum synchrotron applications."

Sulaiman

Wed Apr 26 2017, 04:44PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Physikfan wrote ...

The question is:
How much liquid gallium is necessary to realise a Sprengel pump with liquid gallium at 40Â°C?

In Sprengel's original document he mentions that for mercury, 2.5 to 2.75 mm i.d. is optimum,
(smaller = slower pumping, larger - air able to 'bubble' up past the mercury - not trapped)
so using id = 2.5 mm and drop tube = 1000 mm, volume = 4.9 ml maximum in the tube,
so probably at least 100 g... if mercury.
as gallium is 5.91/13.54 the density of mercury,
the drop tube would need to be > 0.76 x 13.54/5.91 = 1.74 metres MINIMUM,
probably at least 2m required.
If the id is the same then the mass is the same as for mercury, or any other fluid.
(pressure, area and gravity fixed, therefore mass also fixed)

I don't know if it is significant; gallium wets glass and most other materials, mercury does not.

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