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JAMES 0. SCHRECK Univemity of Nonhem Colorado
Greeley, CO 80639
Collapsing Containers Justina L. Brown Northmont High School, Clayton, OH 45315 Rubin r at ti no' Wright State University, Dayton. OH 45435
We live a t the bottom of an ocean of air that exerts a considerable pressure of which we are generally unaware. Otto von Guericke demonstrated this dramatically many years ago with his famous Magdeburg hemispheres that two teams of horses could not pull apart. One typical mode m demonstration is to evacuate a onegallon rectangular paint thinner can. However, these cans are nolonger easily available. Another demonstration is to create a partial vacuum in a paint thinner can or, even more popular, a thinwalled soda pop or beer can by boiling water in the vessel, and then putting the cap on the thinner can or quickly immersinc the upside-down beverace can in cold water (13). In this articie we will describe&eful variations of these demonstrations as well as some svstematic studies. In all cases we use steam either generited externally or internally to the wntainer to sweep out any residual air. At our location, the barometric pressure is about 750 torr. Some relevant vapor pressures of water are (pressure in torr and temperature in C in parentheses): 0(4.6), 10(9.2),20(17.5), 25(23.8), 30(31.8), 40(55.3). Thus, a room temperature of 25 "C decreases the pressure by a factor of about 32 (750123.8) and ice water about 163 (75014.6). These pressure differences brought about by condensing steam are quite adequate to crush many containers. There are some interesting exceptions, however.
lapses. This can be speeded up by cooling with water. A pressure gradient seems to build up in the jug (and the pop cans) and shaking sometimes briefly reverses the wllapse. As the container collapses sometimes sharp creases are formed, and it springs a leak. This also occurs for the pop cans. Screw caps work more satisfactorily than the snap closures, which, in our experience, are more likely not to seal tightly enough. An alternative procedure is to generate steam by boiling water and flushing the container out for 3-5 min before
Plastic Milk Jug
1 cm H,O Aluminum Pie Tin
Plastic Containers
Because metal soda pop cans are small, their crushing is not as dramatic or visible in a large lecture hall as the old gallon rectangular cans. The gallon cans are hard to wme by, but plastic milkjugs in the one and one-half gallon sizes are not. There is an old trick of boiling water in a paper cup (4). We have tried this with milk "iues and thev char and melt, even when placed on a wregauzc. Howevcr, wc have found that makinea "boat" out ofseveral ,we use four) lavers of aluminum Toil that extends about 3 cm beyond t i e edge of the container, and angled up a t about a 45" angle for another 3 cm,that water can be safely boiled directly in these plastic jugs. "L)isposablenaluminum pie tins work well over the wire gauze as shown in Figure 1.After seeing the steam (really condensed water vapor) escape for 3 4 min, the jug's cap is simply screwed on tightly, and it is removed from the ring stand.
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Wire Gauze
Ring
Caution: The jug is hot. Insulated gloves, tongs, or heat pads should be used in handling it.
One satisfying aspect of doing the atmospheric pressure demonstration in this manner is that the jug slowly wl'~uthorto whom correspondence should be addressed 514
Journal of Chemical Education
Figure 1. Set-upfor heating water in a plastic jug.
Metal Containers
2 Lner
Pop eonle
4 Liner
Beaker
Ice Water
Figure 2. Set-upfor putting steam in a plastic pop bottle. removing the tubing that extends to near the bottom of the container, and then sealing. Plastic orangejuice containers work as well as the plasticmilkjugs. Plastic liquid laundry detergent containers satisfactorily crush, and we recommend the live steam for them rather than direct boiling. Plastic liquid bleach containers that are thick-walled do not work well on direct heating and live steam should be used instead. They sometimes are sturdy enough that they do not collapse at all. Transparent plastic soda pop bottles are made from a plastic different from the translucent milk jugs (polyethylene terephthalate versus polyethylene) and are heat shrinkable. Attempts to boil water directly in these soda pop bottles fail due to the shrinkage of the bottle. Live steam has the same effect. However, if the bottle is immersed up to its neck in a large (we use 4 L) beaker containing ice water, then the live steam technique works well with no evident heat shrinkage as shown in Figure 2. Of course, most of the steam entering the bottle is condensed. W~tha vigorow steam generator enough swam escapes to ouree the air in the bottle. Aauick and safe removal ofthe steam tube and sealing results in a satisfactory collapse of the bottle. This is a tough plastic, and we have used some of these pop bottles several times. There are two incidental demonstrations that can be done with plastic pop bottles. The labels also are heat shrinkable. The ring labels can be separated carefully from the bottle by using a small steel rule or similar piece of sheet metal (carefully rounded and deburred, of course).A hair dryer or heat gun used cautiously can get the label to shrink tightly around a beaker. The other demonstration involves drilling a 1-1.5 mm hole in the cap, filling the bottle close to the top with cold water, and screwing the cap on tightly. Directing a heat gun (1500-W hair dryers do not supply heat fast enough) over the pop bottle will cause it to shrink sending a stream of water 1-2 m or more into the air.
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Before describing the experiments with thin-walled popbeer cans, we will discuss our findings with other metal containers. Rectangular one gallon (or other size) metal containers with good sealing caps work well when you can fmd them. Metal ("tin can")juice containersin any size will not collapse because they are designed to "contain" vacuum. Cylindrical ether cans also will not collapse. We punch small (about 6-mm or 114-in.) holes in the full juice containers with a clean scratch awl and then drain the contents. After boiling water in them, the holes are sealed with a strip of black plastic electrical tape. After cooling, any of these sturdy containers will give a satisfactory "hiss" upon unsealing. We have found no differences in the behavior of standard thin-walled steel or aluminum soda pop or beer cans and will simply refer to them as pop cans hereafter. Our interest was to develop reproducible methods for the slow collapsing of these containers because this is more dramatic. The easiest way to work with these cans is to punch an approximately 6-mm hole (in the unopened can) with a clean scratch awl or similar device in the area on a line with the flip-top opening and about one-half way between the center and the rim. (This hole also can be drilled.) The liquid may be sucked out using a straw or "pumped" out into a glass for drinking. Rinse and add the appropriate amount of water, about 25 mL in most cases (see later for variations). The water may be boiled on a hot plate, over a Bunsen burner, or using a propane torch. After steam (condensed vapor) is emitted for about 5 min, remove the can from the heat source (using appropriate protection), and immediately wver the hole with a 4;cm strip of blackplastic electrical tape. Soon the can will collapse slowly in a most satisfying manner. The most commonly available pop cans are those that have already been used and that have rather large openings. Remove the tab ring carefully. Rinse and add water (see the table for volumes).We have tried a variety of tapes (duck, masking, black plastic electrical, package, scotch, fiberglass reinforced, and label tape) to seal these openings. We recommend using the faintly pink 4-in. wide label tape that is used for completely covering labels on envelopes or packages. Cut a piece about 4-in. long. Then cut it into four roughly equivalent pieces. Place each piece on the can carefully so that the tape adheres smoothly with no ridges or pockets. Punch a hole in the same place as before. (Use a sheet metal drill; ordinary drill bits put in ragged holes. The scratch awl is easy to use and makes clean holes.) After boiling, again use a piece of black plastic electrical tape to seal the hole. (Note: Use wide tape for covering the large holes and electrical tape for the small punched holes.) A satisfactory way to seal pop cans is to use the plastic beverage container lids available i n supermarkets or kitchenware stores. A4-6 mm hole is punched off center in Volumes of Water and Times for Soda Pop Cans mL water
boil time (min)
steam time (min)
crush time (s)
Volume 71 Number 6 June 1994
515
the plastic lid using a cork borer. After filling, line up the hole over the tab opening. After boiling, seal as before with a strip of the black plastic electrical tape. Be careful to properly seat the plastic lid tightly on the can. These lids are reusable. The table gives the amount of time it takes when filling the pop cans with various amounts of room temperature tap water. The filled cans are placed on an already heated hot plate. We obtain an interesting effect by using four cans filled with 25,50,75, and 100 mL of water. The cans are placed on the hot plate at the same time. The cans are ready to be removed in about 15 min, and each is sealed with tape as fast as possible. The cans satisfactorilycrush in sequence with a variation of about 1s from the indicated times. Remember, sometimes you can get a can to expand briefly by swirling.
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Journal of Chemical Education
Caution: Hot containera look exactly the same as cold mntainers. Determine the need, and use protection when handling hot containers.
Acknowledgment
JLB was supported by NIH Minority High School Research Apprenticeship Program. We thank all those who pioneered this demonstration. Literature Cited 1. Mebane. R. c . ; R~bolt,T. R.AdwnNres 8"ithAtoms ond M&ulrs; Bwk In. Eoslow, 1991. p 33. 2. 'Fun dthchemistry-AGuidebwkfarK.12 Aetivitid, ~ i i t u t e f m c h e r m c aEdueal
tion lW1.239.143. 3.Kaufman, G.B. J Cdl. Sri. Teoch. 1986, N,364. 4. Liem, T. L. Inuitotions tob'cienn Inp.uiy.2nd ed. Ginn Reas: Lexington, 1981, p 16.
