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 Joule-Kelvin 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 [mp100703.html], 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://en.wikipedia.org/wiki/Sulfur 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.