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.Ê We learned about that in the Baker Safety Course in 1978.Ê But flame arresters have not been standard on those containers,
even with the knowledge of the safety factor.Ê 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.ÊEven 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.Ê 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 demonstrationÊwhere
no flames are used.Ê 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.Ê Then, premeasure the materials before the demonstration.Ê Not every compound being used, such as sodium bicarbonate,Êneeds to be premeasured, but they should
all be in small sized labeledÊcontainers for dispensing.Ê Flammable liquids and corrosives must definitely be premeasured.Ê 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.) ÊBigger is NOT better.
The demonstration should be set up in theÊproper venue.Ê 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,Êappropriate safety
shields, fire extinguisher, and proper PPE.Ê The audience must be at a safe distance from the demonstration.Ê If there is any possibility of liquids or particulaes escaping toward the audience, then safety eyeware is mandatory.
OnceÊthe 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.Ê If the presenter wants the audience to see it again, remove the spent demonstration materials and set up a fresh demonstration.Ê Follow the proper procedures and
do the demonstration again.Ê
There are safety guideline for demonstrations and presentations, but they do not guide the presenter in the safe way to perform the demonstrations.Ê 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.Ê It is not an effectiveÊdemonstration 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.Ê 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,Êare not bright enough or persist long enough to observe spectral lines.Ê For those few elements, the instructor can demonstrate those colors by aspiratingÊ particulates
of the salts through a Bunsen burner flame.Ê My procedure for doing this is on my web site at
http://www.chymist.com/Colored%20flames.pdfÊ(Some photographs of the colored flames are included.)
A good demonstration may provide some entertainment value, but it must provide educational value.Ê 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.Ê That does not mean that something won't go wrong,Êaccidents do happen.Ê In my personal experience, no one has been harmed and nothing has suffered
severe damage.
_________________________________________________________________________
Ê
Ê David A. KatzÊÊÊÊÊÊÊÊÊÊÊÊÊ
Ê Chemist, Educator, Expert Demonstrator, Science Communicator, andÊ Consultant
Ê Programs and workshops for teachers, schools, museums, and the public
Ê 5003 Canby Dr. * Wilmington, DE 19808-1102 *Ê USA
Ê voice/fax: (302) 509-3282 * email:
dakatz45@msn.com
ÊÊÊÊÊÊÊÊÊÊ Visit my web site:Ê
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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