When the Barking Dog Bites the Hand that Feeds It A Safety Caution The demonstration of the spontaneous combustion of white phosphorus better lmown as the '%barkg dog" experiment has been a popular way of showing the powerful chemical reactivity of the element phosphorus in its white allotrooic form for manv "ears. This n o t e is m e a n t t o a l e r t users t o o n e ~ a r t i c u l a wh a z a r d o u s a m e c t of t h i s demonstration. Same time ago I used the "barking dog" demonstration as a part of a series to show oxidation-reduction n. artion. 1 followed all the Chemical Demonstrations. Shakhashiri notes ..... efferta i.. -.. .~~~ ~~~-instructions in -~Shakhashiri's under rhe Hazards sertron that one should wear glows during rhc prrparntmn of rhe phosphonu-cartton d~sullide solutmn and when using the ~ o l u t i o n s This . ~ seemed a good ldea tu me su during the prepanlon ofthe solurmns I wnrc rubber gloves. On the day of the demonstration I picked up a packet of disposable plastic gloves and took them to the lecture hall with me. When I came to the harking dog experiment I donned the gloves and began adding t h e carhon disulfide solution to the fdter papers. As I worked my way down to the last graduated cylinder the first one comhusted and made a loud noise. Agirl in the front row, startled, gave forth with a blood curdling scream. This caused me to jump and some of the disulfide solution sloshed out of the container and onto the plastic glove on my l e e hand. I was revieved I had the glove on, but not for long. I out the battle on the table and was talkine with the class far anlv a few minutes when I noticed they all seemed to be side. I danced a&l was amazed to find on fire. With a soked that mieht ~- &ine "at mv left ~ ~ down~ ~ ~the olastic , elove ~ ~ have made Suprrmnn hlush I got the glove offand laid it upon the table whrrr it continurd m hum. I had a few pa~nful reminder8 on rhc tlp of my forefinger and index finger of what mrlrcd plssttc fwla l!ke. The students thought ~t was part of the act, hut of course it wasn't. I have tried no experiments with neoprene gloves or other types to see what happens when they are doused with carbon disulfide-phosphorus solution, but my experience dictates that plastic gloves should not he used a t any point during this demonstration and caution should he exercised in the choice of gloves before carrying out this demonstration. ~~~~~
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'~hakhashiri,B.Z. ChemicalDemonstrations: University of Wisconsin Press: Madison, WI, 1983:Voi. 1. pp 74-76
John D. Worley S. Norbert College DePere. WI 541 15
Volume 69
Number 3 March 1992
241
