ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************

A word of caution: since atmospheric pressure, about 15 pounds per square inch in customary units, translates into about one ton per square foot, a designer of any chamber being evacuated should be aware of the strength needed, especially when large-sized chambers are to be evacuated.  The tube being discussed, about 30 cm (or one foot) diameter, would presumably have flat end caps which would be subjected to an inward force of about 0.8 ton if there is vacuum inside and normal atmospheric pressure outside.  Recall the heavy, thick glass front faces of older television picture tubes, needed for strength to prevent implosion.

Albert J. Read
Director Emeritus, Science Discovery Center of Oneonta
State University of New York, College at Oneonta


-----Original Message-----
From: Informal Science Education Network on behalf of Ian Russell
Sent: Mon 10/23/2006 9:00 AM
To: [log in to unmask]
Subject: Re: Clear cylinders and pulling a vacuum.
 
ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************

Here in the UK it is possible to buy long Perspex (=Plexiglass) tubes 
with 30cm diameter. I have successfully produced a high-vacuum 
exhibit using this material. Mine used only a short length of ~30cm 
tube, but a longer length should be equally resistant to external 
pressure. Be careful to avoid bending forces though. Even with thick 
walls, it is possible to see inside with perfect clarity because this 
material is very precisely formed and highly transparent.

There's a photo of my version here (scroll down to "Silence of 
space") http://www.interactives.co.uk/hands_rumbo.htm


[log in to unmask] * http://www.interactives.co.uk
*
Give people facts and you feed their minds for an hour.
Awaken curiosity and they feed their own minds for a lifetime.
*
Ian Russell 

***********************************************************************
More information about the Informal Science Education Network and the
Association of Science-Technology Centers may be found at http://www.astc.org.
To remove your e-mail address from the ISEN-ASTC-L list, send the
message  SIGNOFF ISEN-ASTC-L in the BODY of a message to
[log in to unmask]


***********************************************************************
More information about the Informal Science Education Network and the
Association of Science-Technology Centers may be found at http://www.astc.org.
To remove your e-mail address from the ISEN-ASTC-L list, send the
message  SIGNOFF ISEN-ASTC-L in the BODY of a message to
[log in to unmask]