An "Egg-Splosive" Demonstration Robert Becker Kirkwood High School, Kirkwood, MO 63122
A wide varietv of containers has been used for illustrating the explosive power of a wmbustible gaseous mixture.' These ex~losionsare especially impressive when set up as time-delayed reactions-with a flame burning over an upper orifice, then backfiring into the wntainer.' The following demonstration is the latest addition to this bevy of booms, but it utilizes one of nature's oldest containers. Materials one egg, any size an ice pick or a sharp nail 1&15 cm of wire piece of masldng tape or putty source of hydrogen gas (either a lecture bottle or a ZniHC1 reaction) t h e upper portion of a plastic 2-L soda bottle ta serve as a small base for the egg Procedure Wash the egg thoroughly. Then, with the ice pick or nail, eentlv" tan a small hole ( 2 3 m m in diam.) in the to^ (narrower eni) of the egg and a slightly larger hole (3-4hm in diam.) in the bottom. Insert the wire and stir UD the volk. Over bowl, blow into the small hole to force the egg'a"contents out throueh the lareer hole. This mav take some doing! ~ i n soutihe e inside several times, and allow the egg to drv ovemieht at room tem~eratureor for 30-40 min in a wakn (100'~) oven.
-
a
Demonstration Caution: The demonstrator should wear goggles and a safety shield should be plated between the egg and the au-
dience. Fill the egg completely with hydrogen gas. To do this, cover the top hole with a piece of tape or putty and introduce the hydrogen through the bottom hole via a long capillary tube extending upward almost to the top of the egg. Use a generous volume of hydrogen to ensure a thorough flushing of the egg. Using the top of the soda bottle as a support, stand the egg in an upright position with the taped hole on top. Then, to initiate the combustion reaction, simply remove the tape and hold a burning match briefly to the top hole (see the figure). Stand back! 'Alyea, H. N. In Tested Demonstrations in Chemistry (1965) several containers for the Hz + O2explosion are referenced including: soap bubbles, balloons, cardboard milk cartons [Fine, I. J. Chem. Educ. 1931, 8, 9291; iron pipes [Walton,J. H. J. Chern. Educ. 1942. 19, 4531; Pyrex tubes wrapped in Scotch tape [Ransford,J. E., S. J. J. Chern. Educ. 1950, 27, 2011; bell jars [Sellers,J. J. Chem. Educ. 1927,4,914];andtin cans [Arenson, S. B. forwarner,J. C. J. Chem. Educ. 1941, 18,1681. Shakhashiri. 8.2. In Chemical Demonstrations, Vol. 2 (University of Wisconsin Press, 1985),delayed-explosion demonstrationsfor hydrogen in bell jars and in art off2-L soda bottles (131-136) and for methane in empty paint cans (196-197) are discussed. Irwin Talesnick pelforms the tirne-delayed hydrogen explosion in an inverted Pringle's potato chip canister, and the blast sends the container flying.
ohole wer)j(
/
egg
I
'
,top of 2-L bonle
et-upfor "eggs-sploding"the egg After a small initial "pop" sound, nothing appears to happen. Then, a short while later: "BOOM," and the egg is gone. Discussion The initial pop is caused most likely by a small portion of the hvdroeen leakine " - out.. mixine with the air immediatelv above the hole and forming a minute wmbustible mixture there. Then, as more hydrogen gas slowly escapes through the ton hole. it continues to react with the oxveen in the air and bums with a n essentially invisible and silent flame. At the same time, oxygen-containing air is being drawn up into the egg through the bottom hole and mixing with the remaining hydrogen there. When enough air has entered to form a combustible mixture inside the egg, the flame backfires down through the hole and ignites the mixture. Since the reaction is very exothermic, and since the holes in the egg are not large enough to accommodate the rapid expansion of the gases, the pressure inside the egg increases rapidly and explodes it into several small pieces. The time-delay between the initial lighting m. - of the eand the subsequent explosion can vary quite significantly, lastine anvwhere from a fraction of a second UD to 3 0 4 0 s " depending on the size of the egg, the size of the two holes, and the extent to which the air inside the egg was effectively flushed out by the hydrogen. When the eee described above is chareed with methane rather than hydrogen, the demonstration fails, for the flame bums out almost immediately, long before a combustible methandoween mixture is reached. This amears to . be a result of the small hole size, with the methane unable to leak upward a t a rate sufficient for sustaining a flame above the egg. In order for a methane flame to sustain itself, the holes must be enlarged substantially. When this is done, as described below, the demonstration works but with a noticeably different outcome.
-
-
--
-
--
-
.-
&
Volume 69 Number 3 March 1992
229
Variation The Flashina Eaa
- --
procedure described for the hydrogen Follow the egg, but make the holes each about 10 mmin diameter and charge the egg with methane from the gas jet. Unlike hydrogen, the methane burns quite visibly, starting off bright orange and 15-20 cm tall and diminishing to a small blue flame a s the methane concentration inside the egg de-
230
Journal of Chemical Education
creases. When the flame appears to be completely extinguished, the combustion reaction backfires into the egg, similar to the backfiring for hydrogen. However, since the holes in the egg are so much larger, rather than an explompm,,sound is produced and the entire egg sion, a
with a quick, flash. lights Although perhaps somewhat less dramatic than the hydrogen egg, at least the methane egg is reusable!
