This demo is not a "barking dog" demonstration. It is a variation of the "whoosh bottle" demo. See https://www..flinnsci.com/media/484580/95010-r.pdf My personal opinion is that this is not a demo to do at home nor should it be performed by an untrained demonstrator. (The Flinn description, referred to, here, lists the safety precautions.) The video states that all the oxygen is used up in the reaction. That is not true. In the "classic" whoosh bottle demonstration, the bottle opening is quickly covered, the bottle and fuel agitated, and a second spark or flame is introduced. There is sufficient oxygen for a slow flame to burn the fuel through the bottle.
As shown is the video, there are no safety precautions taken. The bottle appears to be a standard household bottle which is most probably not suitable for this type of reaction and could break or shatter during the reaction. (Even a large 5 gallon plastic water bottle becomes weakened by repeated use for this demonstration.) Such a bottle should be wrapped with a clear plastic coating such as Contact adhesive shelf liner, which would be readily available to a home experimenter, to protect against the glass shattering. There should not be any excess alcohol in the bottom of the bottle as the mouth of the bottle shown is too wide and can allow enough fresh air into the bottle to allow the alcohol to continue to burn. Although isopropyl alcohol does burn with a yellow flame, it is still not bright enough to see in a well lit room. Methanol and ethanol burn with a blue flame that is even less visible. In addition, the video shows the reaction being repeated without bottle being cooled to room temperature and insuring that there are no flames in the bottle. A screw cap should not be used as it can allow for a pressure build-up in the bottle. Safety shielding is required.
If someone wants to do this demonstration, they should be adequately trained in the procedure. They should know the safety precautions necessary, and what to do in the event of an accident.
The true barking dog demonstration uses a mixture of carbon disulfide and nitrous oxide which is totally unacceptable in a non-laboratory environment.
David A. Katz
Chemist, Educator, Expert Demonstrator, Science Communicator, and Consultant
Programs and workshops for teachers, schools, museums, and the public
133 N. Desert Stream Dr. * Tucson, AZ 85745-2277 * USA
voice/fax: (520) 624-2207 * email: dakatz45**At_Symbol_Here**msn.com
Visit my web site: http://www.chymist.com
_________________________________________________________________________----- Original Message -----From: Patrick A CeasSent: Wednesday, April 27, 2016 12:10 PMSubject: [DCHAS-L] "safe" barking dog demoJust a quick yes or no, please. Would you lump the "Safe Barking Dog Demo" in the same category as the Rainbow Demo & Tornado Demo (i.e., it is an open flame demo, where additional flammable fuel -- let's say 95% ethanol -- could be added to an already confined ignited situation, therefore it is not prudent to perform, especially at a local grade school). We are having a discussion about it.Here are two links that show/explain it:http://chemistry.about.com/od/funfireprojects/a/Fire-In-A-Bottle-Barking-Dog-Chemistry-Demonstration-Alternative.htmThanks.Pat--
Previous post | Top of Page | Next post