Thank you, Peter, for stating the best solution for proper demonstrations: proper preparation and the knowledge of what you are doing and what all the hazards are.
In my more than 20 years of teaching teachers how to do chemical demonstrations, I have always stressed safety.
The videos on flame jetting are excellent. I fully support the use of flame arresters on containers of flammable liquids. We learned about that in the Baker Safety
Course in 1978. But flame arresters have not been standard on those containers, even with the knowledge of the safety factor. J. T. Baker never put them on their 4 L bottles of those liquids.
For science teachers doing demonstrations with flammable liquids, not only are there not flame arresters on their containers of flammable liquids, but some of these
teachers bring large containers of those liquids into their classrooms or lecture halls. That's just asking for a possible accident. Even with the proper knowledge, you can't fix stupid.
We went through the pros and mostly cons of the rainbow flame demonstration on this listserve over a year ago. Yes, you can do a rainbow flame demonstration! Yes,
there are alternatives, but the rainbow demo is impressive as one can observe the colors side-by-side.
As a career chemistry teacher and demonstrator, I vigorously oppose the banning of what may be a very good demonstration and the banning of methanol and other alcohols
or flammable solvents, even if those liquids are used for a demonstration where no flames are used. I prefer to see the banning of ignorant invidivuals who don't know what they are doing or what they are working with. Administrators should be asking their
science teachers about their training and experience in the proper presentation of demonstrations. A response from a teacher such as "I've never had a problem with this before" is totally unacceptable.
The proper procedure for any demonstration is test it in advance in a safe area. Then, premeasure the materials before the demonstration. Not every compound being
used, such as sodium bicarbonate, needs to be premeasured, but they should all be in small sized labeled containers for dispensing. Flammable liquids and corrosives must definitely be premeasured. If the presenter thinks that the demonstration is too small
for good audience visibility, project it onto a screen. (Many schools have document cameras in classrooms which can be used.) Bigger is NOT better.
The demonstration should be set up in the proper venue. That means good ventilation, safe surfaces for the demonstration or a safe cover for that surface, means
to safely contain the reactions, overflow and splashing, appropriate safety shields, fire extinguisher, and proper PPE. The audience must be at a safe distance from the demonstration. If there is any possibility of liquids or particulaes escaping toward
the audience, then safety eyeware is mandatory.
Once the demonstration is assembled, all remaining chemicals and equipment must be removed from the immediate vicinity before initiateing it..
Under no circumstances should a demonstration be "refueled" to prolong it. If the presenter wants the audience to see it again, remove the spent demonstration materials
and set up a fresh demonstration. Follow the proper procedures and do the demonstration again.
There are safety guideline for demonstrations and presentations, but they do not guide the presenter in the safe way to perform the demonstrations. They do not provide
any safer and effective alternatives, such as substituting ethanol for methanol in the rainbow flame demonstration.
The rainbow flame demonstration is a way to show the range of colors of different chemical salts. It is not an effective demonstration to allow students to use small
spectroscopes to observe spectral lines of those metal elements - the flames do not always last long enough to view the spectra. The alternative methods using wood splints, or similar apparatus, are safe for individual student groups to do in a proper laboratory
setting.
In some cases, colored flames produced by these alternative methods, are not bright enough or persist long enough to observe spectral lines. For those few elements,
the instructor can demonstrate those colors by aspirating particulates of the salts through a Bunsen burner flame. My procedure for doing this is on my web site at
http://www.chymist.com/Colored%20flames.pdf (Some photographs of the colored flames are included.)
A good demonstration may provide some entertainment value, but it must provide educational value. That educational value may be provided by follow-up experiements
in a laboratory.
In my almost 50 years of presenting demonstrations, I have maintained a 100% safety record. That does not mean that something won't go wrong, accidents do happen.
In my personal experience, no one has been harmed and nothing has suffered severe damage.
_________________________________________________________________________
David A. Katz
Chemist, Educator, Expert Demonstrator, Science Communicator, and Consultant
Programs and workshops for teachers, schools, museums, and the public
5003 Canby Dr. * Wilmington, DE 19808-1102 * USA
voice/fax: (302) 509-3282 * email:
dakatz45**At_Symbol_Here**msn.com
Visit my web site:
http://www.chymist.com
_________________________________________________________________________
----- Original Message -----
Sent: Saturday, June 22, 2019 9:15 AM
Subject: Re: [DCHAS-L] Letter to the National PTA regarding the rainbow flame
demo
One thing I notice about this letter and many other comments about this demonstration directed to educators is the frequent absence of guidance on how to perform
it more safely, or on alternative, less hazardous, demonstrations that would illustrate the same principles.
In my experience, it is usually more effective to provide alternatives than to simply say "don't do that."
Decades ago, my then boss at Princeton University used to say to faculty members something along the lines of "I am not telling you that you can't to that; I am telling
you that you can't do it in the way you have been accustomed to doing it."
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