From: SFPhysics@aol.com
Date: Tue Oct 22 2002 - 02:05:46 PDT
From: SFPhysics@aol.com Message-ID: <19d.aa0b48a.2ae66eea@aol.com> Date: Tue, 22 Oct 2002 05:05:46 EDT Subject: Whosh Bottle - Vacuum Bell Jar - Safety
Thanks Eric.
In reviewing the explosion in Bakersfield I suspect that the ambient lab
temperature may have been higher than usual causing the vapor pressure of the
methyl alcohol (CH4O) to be higher and also accelerating the reaction.
Bakersfield in August can be in the low 100's Fahrenheit. The Chem teacher
in my school used Ethanol (CH3CH2OH) with its lower vapor pressure and slower
combustion rate in the San Francisco normally cool ambient temperatures. The
smaller methyl molecule is too close to the fast combustion propane (or
methane) which I used for my potato canon in the ballistics demonstrations
for me to be comfortable using it. Chem people please enlighten me if my
thinking is flawed.
On any experiment that even remotely has the possibility of explosion or
implosion there should be adequate safety precautions. A quarter inch mesh
wire screen purchased from a hardware store and made into a protective cover
is what I used for all my bell jar vacuum demonstrations for 33 years and was
lucky enough never to have an implosion. Today there is Lexan (the trademark
of a bullet resistant polycarbonate acrylic) which could be placed in a
sturdy frame between the demonstration and the students. I got a sheet from
the school district glaziers who were replacing broken windows and made a
frame myself. That way I had the wire screen and the Lexan for those last
few years. This was because my bell jar was very large and when evacuated
had very great forces on it.
Lastly, anyone know where I may purchase a small quantity of Ethanol to try
the experiment myself? No one will sell this to me now that I am a common
citizen who is not connected to a school.
Best wishes to all,
Al Sefl
Retired but keeping busy...
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