1997-2006 Academic Years
12 September 2000 Bill Shanks (Joilet West HS, ret)
held up a starter used with fluorescent light fixtures. It is a cylinder about 4-5 cm long and about 2-3 cm diameter. He took it apart to show us that the inside apparently had two parts, something that looked silvery in color (mercury?) on the inside, and the other was maybe some sort of small coil. Bill asked, "How does it work? What are these parts? What does it do?"
In the discussion that followed, someone pointed out that a fluorescent bulb has filaments at each end, and the starter causes current to flow in the filaments, making them hot enough to vaporize mercury in the tube, so the mercury could then be ionized by the high voltage (supplied by the ballast, ie, high voltage transformer) applied across the tube. Once the mercury is ionized, the ions give off light when atoms go back to states of less energy. The light energy, mostly not in a useful visible range, then reaches the phosphors coating the inside wall of the fluorescent bulb, and the phosphors then absorb that energy and emit light in a useful range for us to see by. Rapid start fluorescent bulbs do not require starters (which eventually go bad), apparently because the ballasts provide a voltage high enough to ionize the mercury vapor that is present at room temperature. Maybe someone will supply us with definitive answers about how fluorescent bulbs and their fixtures work at a future meeting?
This got us into a discussion of possible dangers of fluorescent bulbs - the hazards of mercury. Many of us recalled "playing" with silvery liquid mercury in our classrooms found in the barometers. And Earl Zwicker remembered how his 8th grade science teacher heated a red, powdered solid (mercuric oxide) in a beaker and it turned into the liquid, silvery mercury. Lee Slick told us that oxygen is driven off, and if it was captured, this was an easy way to get oxygen for use in experiments. Earl pointed out that mercury vapor from the liquid was very dense, and stayed close to the floor. The most dangerous forms of mercury are in the form of organic compounds which can be ingested. Manufacturing processes may put mercury into rivers and lakes, and it may be ingested by fish as organic compounds. Then we (and other creatures) eat the fish. Ann Brandon pointed out that not long ago - and even these days - we had warnings not to eat too much fish from our lakes, because of the hazard of mercury. But she said that fish that were caught during the early 1800s - before manufacturing processes could have put mercury into the water - showed much the same levels of mercury being found today!
Bill Shanks drew a diagram on the board showing a "motor" consisting of a battery, a pool of mercury, and a spring suspended above the pool with its bottom end touching the mercury pool surface. One terminal of the battery was connected to an electrode placed at the bottom of the mercury pool, and the other terminal to the top end of the spring. A current would then flow, the coils of the spring would be magnetically attracted to each other - causing the spring to shrink - which moved the spring out of contact with the mercury pool, interrupting the current. The spring would then relax to make contact again, and the cycle would repeat, making the spring jump up and down. What about mercury vapor that was released into the classrooms where this experiment was done by science teachers? Who knows?
12 September 2000 Lee Slick
pointed out that the Mad Hatter in Alice in Wonderland was mad from the effects of mercury used in the manufacture of hat bands. Apparently this sort of thing really happened in the past! Lee also informed us that mercury cost about $60 per pound about 5 years ago.
05 March 2002: Fred Farnell (Lane Tech HS Physics) -- Dangers of
Fred saw a tank truck containing Liquid Hydrogen on the Dan Ryan Expressway, and raised the question of safety. This issue was discussed, and it was generally felt that Liquid Hydrogen is probably no more dangerous than such materials as Liquid Natural Gas [LNG], Kerosene, Propane, Butane, or Gasoline --- and that the most dangerous material for transport is considered to be Liquid Oxygen, according to Physics Guru and Sage Bill Shanks.
Here is an excerpt from a BBC Report on the Power of Hydrogen:
... Hydrogen can be a dangerous explosive and the thought of carrying large amounts in the tank of a car could be a bit disconcerting. But Detlef Frank believes the dangers of hydrogen are no greater than many other hazards of daily life:
‘The danger is not higher, it is different. Hydrogen is a gas that is 18 times lighter than air. So if you have a hole in your tank, for example, it just evaporates straight up. If you have a hole in a tank of, let's say, a diesel truck, you will find a little lake under your vehicle. If you are in an accident and this burns then you will be in a very bad condition. So it depends on the type of accident you have.'
See also the website of the California Hydrogen Business Council: http://www.californiahydrogen.org/, as well as of the Institute of Ecolonomics: http://www.ecolonomics.org/, founded by Dennis Weaver [remember Chester?].
Porter Johnson mentioned that hydrogen gas has a positive Joule-Kelvin
[or -Thomson, who later became Lord Kelvin]
coefficient over a
wide range of temperatures: [http://en.wikipedia.org/wiki/Joule-Thomson_effect]
The decrease in temperature which takes place when a gas expands through a throttling device as a nozzle. Also called Joule-Thomson effect. The rate of change of temperature T with pressure P in the Joule-Kelvin effect is called the Joule-Kelvin coefficientInteresting questions, Fred!
l = [ dT / dP ] hwhere h denotes constant enthalpy. For the Joule-Kelvin effect to take place the gas must initially be below its inversion temperature; if above the inversion temperature, the gas will gain heat on expansion. The inversion temperature of hydrogen, for example, is approximately -183 °C
07 May 2002: Don Kanner (Lane Tech HS, Physics) Liquid Nitrogen
Don described an experiment in which he poured Liquid Nitrogen into a bin to form a layer about 2 cm deep, and then placed a beaker containing about 20 ml of water slowly into the bin. When the water was solidly frozen, he and the class observed that the water had frozen into ice that had formed a peak at the center of the beaker. How come? The effect apparently occurs because water expands when freezing, since ice is less dense than water. The ice forms first near the outside of the glass, causing the liquid inside to be pushed upwards. One can also see "central peaks" in ice cubes formed in refrigerators, for the same reason. We then discussed the inherent dangers in handling Liquid Nitrogen LIN (or LN). In addition, taking precautions because of its low temperature [71 K], one must be careful NEVER NEVER to close or clog the vents on a LIN container. The liquid continually vaporizes in a room temperature environment, and in the process of evaporation its density is reduced by a factor of about 1000. Unless the vapor is allowed to exit the LIN container, a dangerously high pressure [up to about 1000 atmospheres] will arise fairly quickly. Good, Don!
25 February 2003: Roy Coleman [Morgan Park HS,
Replacement of Mercury Thermometers
Roy explained that he had taken all the mercury thermometers in the physics laboratory to central headquarters, where he gave them to somebody in a hazardous waste disposal costume, in exchange for new thermometers that did not contain mercury. When he read the documentary information, he learned that these thermometers contained toluene, kerosene, aniline compounds, and other Volatile Organic Compounds, which posed a potentially significant carcinogenic and hazardous risk. Roy expected to receive thermometers containing a colored alcohol-water mixture, but because of some cross-up in the order, he had received the wrong thermometers.
21 October 2003: "F" Lee Slick [Morgan Park HS,
physics] More on Matches and
burning stone = sulfur]
Motivated by the Paper Match Rocket presentation by Bill Blunk at the last meeting, Lee held a contest in his science class to see which team could shoot a rocket over the greatest distance. The girls team won, because they followed the directions more carefully! Lee also raised the question of the chemical reactions involved in burning sulfur in matches. The usual reaction is given as S + O2 ® SO2, which is misleading in several respects. First, burning sulfur in air results in a mixture of SO2 and SO3, depending on the temperature and the amount of oxygen present. In a match, the production of SO3 dominates that of SO2, because of the lower temperature and oxygen-enriched environment. Second, the sulfur is usually present in the poly-atomic form S8. Thus, a more correct chemical reaction would be S8 + 12 O2 ® 8 SO3. Put that in your pipe and smoke it -- making sure to use non-toxic matches in lighting your pipe! Good work, Lee!
For additional information see the websites Sulphur and its Compounds: http://www.jghs.edu.ky/Departments/Chemistry/chwssulp.htm and The History of Matches: http://inventors.about.com/library/inventors/blmatch.htm.
06 April 2004: John Scavo called attention to the Energy Information Administration (DOE) website on Oxygenates in Gasoline: http://www.eia.doe.gov/emeu/steo/pub/special/mtbe.html. For additional information see the USGS website on Fuel Oxygenates: http://toxics.usgs.gov/definitions/fuel_oxygenates.html.
20 April 2004: Dihydrogen monoxide: threat or menace? [Chicago Reader, 05 April 2004]. "The city council of Aliso Viejo CA almost voted to ban dihydrogen monoxide -- H20, alias water -- after being informed that it was an odorless, colorless, tasteless compound that could kill you if you breathed it in. ... No word on whether anyone in the local government ever passed high school chemistry." Thanks to Bill Colson for this little tidbit.
25 November 2005: Bud Schultz (Aurora Middle
Bud started talking about temperature, a topic he covers in his various science classes (see also his handout). Bud's students often ask why we define and measure temperature the way we do. When posed with this question Bud has the students do a thought experiment with a balloon: as it is cooled in a freezer, it shrinks; as it warms up again it gets bigger. This correlates with a decrease and then an increase in the kinetic energy of tje air molecules in the balloon. He found that one experiment particularly excited the interest of his students: the "Fire Piston" (as Earl pointed out, is also known as a Fire syringe). (See the websites http://www.onagocag.com/piston.html and http://en.wikipedia.org/wiki/Fire_piston.) The fire piston is really an ancient device, but Bud showed us his newer version:. a glass, cylindrical tube with its bottom end closed off. As we watched, Bud placed a small (dime sized) piece toilet tissue in the bottom of the tube. He then held up a rod (about 25 cm long) with a piston at its end. The piston was fitted with O-rings. Holding the rod, he slid the piston into the top of the tube. With the lights dimmed, Bud ran the piston down into the tube as hard and quickly as he could. There was a bright flash of light at the bottom of the tube! Amazing! We then could see that the tissue had ignited and burned. By rapidly (and adiabatically) compressing the air in the tube, the air temperature was raised high enough to ignite -- reminding us of Ray Bradbury's novel Fahrenheit 451. Bud told us that this really galvanized his students to ask a lot of questions, and take a real interest in trying to understand how it works. Thanks, Bud!
07 February 2006:
Terry Donatello (Weber HS, retired!)
Terry started by noting that with the high price of oil and fears of carbon dioxide buildup in the atmosphere, nuclear power is on the upswing. The activity involves a game (Nuclear Sciences, described in the November 1990 issue of the journal Re-actions, published by the American Nuclear Society: http://www.ans.org/pi/edu/teachers/reactions/). It is played with a special deck of cards (handmade by Terry), each with a step in the nuclear chain reaction. There are seven different cards (steps) in each complete set. The "game" is best played in groups of about three or four, and a full deck will contain as many full sets as there are players. The cards are dealt to all players (5 cards each) with the remaining cards placed in the center. The object is to be the first one to get a complete set of seven cards (from the initial dealing and cards picked up from the pile in the center), describing the following complete sequence of steps:
We continued with a brief discussion of radiation dosimetry: http://en.wikipedia.org/wiki/Dosimetry. A person's average dose is 350 millirads per year -- slightly higher for those who live at higher altitude. Significant tissue damage occurs at a much higher level -- around one hundred rads. Foods containing potassium (bananas, oranges, potatoes, and meat) are somewhat radioactive, since about 1% of potassium occurs as the radioactive isotope K40. It was also mentioned that the dust accumulated on the screen of a television set or computer monitor may be somewhat radioactive, because ions from decay of Radon gas and Carbon-14 are attracted to that surface. For details see the Amateur Radiation Detection and Experimentation webpage http://www.blackcatsystems.com/science/radiation.html, from which the following has been excerpted:
"Did you know that the dust that's in the air and settling all over your house (and computer monitor) is radioactive? It's true, it contains radioactive decay products from naturally occurring Uranium and Thorium.
As an experiment, I wiped some dust from the TV screen onto a tissue, and placed it in front of the radiation detector. The reading went from a background reading around 10 CPM to around 1300 CPM, or 130 times the (background) reading!"
18 April 2006:
Jeff Terry (Professor of Physics,
Fun with liquid nitrogen
Following a suggestion by Don Kanner, Jeff poured out some liquid nitrogen from a 25 Liter Dewar container into a Styrofoam™ picnic cooler, and then into its upside-down lid on the table. Into the liquid nitrogen he then placed a 50 mL Pyrex ™ beaker containing about 25 mL of water. After about 10 minutes we checked the ice in the beaker and it had frozen so that the top surface was a nicely formed cone. This occurred because the water froze from the outside inward, and the volume of the ice was greater than that for the corresponding amount of water. The extra-volume ice was forced to go to the center of the beaker. Neat!
Jeff then took a moderately sized piece of dry ice and broke it into fairly big chunks (about 4 cm on a side) with a wooden mallet and then into much smaller (sand-sized) pieces. Jeff noted that a recent analysis of the material collected from a comet suggested that dusty rock material in the comet must have been formed at high temperature, and not at low temperature! This analysis stands in contradiction to the standard models of comet formulation in the Oort cloud of our solar system -- for details see Life under Bombardment in the 27 November 2000 issue of Astrobiology Magazine: http://www.astrobio.net/news/. Jeff then filled the the Styrofoam™ picnic basket about half full with liquid nitrogen. Jeff noted that the liquid nitrogen is cold (77 K), although not quite so cold as outer space. We mixed various "comet ingredients" to produce our comet: water, dry ice (solid carbon dioxide), dark Karo™ Syrup (organic material), ammonia, dirt, and some igneous stones. The recipe is given below.
The ingredients were mixed in a garbage bag and triple bagged, adding the dry ice (a few bigger chunks and some of the smaller stuff) last. They were mixed and shaken, then plunged into the liquid nitrogen, and held there for a few minutes. As the contents got colder the volume shrank. Jeff then opened the bag and removed the "comet". Just as we have heard comets described -- we got a dirty snowball! As we passed the comet around, we could hear it crackle as the CO2 sublimed away.
Jeff reminded us that dry ice -- and especially liquid nitrogen -- are potentially dangerous materials, which should be handled only with serious precautions. There is severe danger of frostbite with even brief exposures to dry ice or liquid nitrogen. In addition, Jeff pointed out that one liter of liquid nitrogen results in about 10,000 Liters of nitrogen gas N2. Thus it is dangerous to have very much liquid nitrogen in a confined space -- suffocation due to lack of oxygen gas is a real possibility.