Banned Chemistry Supplies

Editor,

I recently tried to order some chemicals for home use by my company and was turned down by the Aldrich Chemical Company.

It would appear that buying chemicals and related equipment from, for example, Fisher Scientific, is now impossible. I have been able to buy some chemicals for photography and plant biochemistry.

I found a Drug Enforcement Agency (DEA) list of "watched" chemicals. Just about every common chemical that anyone would use was on the list, including sodium sulfate, acetone, ethyl alcohol, methanol, acetic acid, and citic acid.

It would appear that amateur science involved with chemistry and crystal growing is now nearly impossible. When I was in high school in the 1960s, I used to carry out experiments involving analytical chemistry (titrations), inorganic qual tests and spot and flame tests, and organic synthesis of such compounds as acetanilide, fluorescein, eosin, and azo dyes. Now all of this would be impossible. All forms of phosphorus are on the DEA watch list.

There has been discussion on TV of illegal drugs using red phosphorus. In Mary Elvira Weeks excellent, but old, "Discovery of the Elements," she discusses how phosphorus was first prepared by heating a mixture of urine and sand in the 17th century. This would probably make a BAD amateur project because the yellow phosphorus is highly toxic and flammable.

Sincerely,

Howard McPherson

Readers: Have you had problems acquiring materials and supplies for legitimate scientific purposes? Please send your report to "Backscatter." Please type "Backscatter" in the subject line. An editorial in this installment of The Citizen Scientist addresses the issue raised by Dr. McPherson and related matters. Editor.

Thanks to Shawn Carlson "for Keeping Science Alive for the Rest of Us"

If I can help, I am willing. My web page skills are limited to HTML coding and a little Javascript. Though I have not been in the field for a very long time, my drafting skills are good, and I have also worked as a commercial artist. I have software to convert to different graphic file formats. I have a scanner and digital camera. If you see anything skill-wise or resource-wise that may be of service then please let me know.

Meanwhile, thanks, Shawn, for keeping science alive for the rest of us.

Yours,

Steve Mills

Remembering Jim Scanlon, Citizen Ozone Scientist

Dear family and friends of Jim,

I have been thinking two week about Jim loss, he was a very good kind of person, truly and reliable, my family will miss him too much like as I will miss to my friend, also all the team here in the Ozone Laboratory in Punta Arenas. Perhaps we could finish some work by him.

I could write too many things about Jim, but I will do other things he would want.

Best wishes for all,

Andrés Hernández S.
Laboratorio de Ozono y RUV
Universidad de Magallanes, UMAG
Centro de Estudios Cuaternarios, CEQUA
Avda. Bulnes 01855
Punta Arenas, Chile

Einstein's Tea Leaves Revisited Editor,

By coincidence this is the second time in the past month or so that someone has requested an explanation of why tea leaves gather in the center of a stirred cup of tea, rather than at the cup walls (see "Einstein's Tea Leaves" in "Backscatter," The Citizen Scientist, 17 June 2005). Here is a slightly modified version as I put it to a Dutch colleague of mine.

When a person stirs a liquid in a cup, they create a primary flow of the liquid that involves a constant rotation around the center of the cup. Almost like the rotation of a solid body. In order to go around in circles, which involves acceleration toward the center of rotation, the liquid requires a centripetal force on each unit mass. A pressure gradient directed outward through the rotating fluid, and terminating at the solid wall of the cup, supplies this force; and a person can see the effect of this pressure gradient by noticing that the rotating fluid free-surface is shaped like a parabola with the highest fluid surface out near the cup rim. This state of affairs is not in equilibrium, unfortunately, and there develops a secondary flow of liquid which is the real focus of our attention in explaining the behavior of the tea leaves.

This secondary flow of liquid depends on the free surface of liquid in the cup, and friction (viscosity) of the liquid at the cup surface. It occurs in the following way. Viscosity prevents any relative motion between the liquid and the cup at the point of contact. In effect the fluid is "stuck" to the solid surface of the cup, and must come to rest there. A fluid dynamicist would say that there is fluid in a thin "boundary layer" near the solid cup surface in which fluid behaves differently than it does in the bulk of the primary flow. Fluid is also at rest along a vertical line at the exact center of rotation near the center of the cup. But there is a greater height of fluid near the cup wall than there is at cup center, and what results is a pressure gradient that sends fluid along the floor of the cup inward. This disturbs the basic solid rotation of liquid throughout the cup.

Thus a secondary flow now develops that consists of fluid that flows inward at the bottom of the cup, rises at the center of the cup (center of rotation actually), flows outward near the surface, and finally downward along the walls. This secondary flow will sweep loose material, like tea leaves, toward the center of the bottom of the cup. A fluid dynamicist would say that there is a "point of stagnation" on the bottom of the cup near the center, and once materials reach this stagnation point they remain there. Eventually this secondary flow will de-spin the liquid, flatten the surface, and bring everything to a state of rest.

It is interesting to speculate about how the flow of tea would change if one were able to put a rigid lid on the cup of tea that would eliminate any free-surface with a parabolic shape. Perhaps this is a good challenge to the readership.

Regards,

Kevin Kilty

Another Tea Leaves Explanation

Editor,

When you stir the liquid in the container, which I assume is round, you create a whirlpool, which does not throw the leaves outward. The center of the whirlpool turns faster than the outside, which cause the leaves to to be drawn into the center. This is like an ocean whirlpool. A skater draws in his/her arms to increase the speed of rotation.

Anna Hillier

Einstein Himself Explains Meandering Tea Leaves

Editor,

"Albert Einstein And Meandering Rivers" by Kent A. Bowker contains Einstein's explanation for the helical flow of tea leaves.

Ralph J. Coppola

Art Winfree, the Butterfield Encoder and the Benham Effect

Editor,

I just signed up for SAS, and I enjoy your newsletter.

In some old pages I ran into something very interesting, and I have a question.

I am a physics teacher, and I am preparing a lesson series on Benham’s effect. On your site, the late Art Winfree had a page devoted to the Butterfield encoder, a color TV system that uses Benham’s effect. Luckily the page is still on the web. Winfree mentions on his page that he had footage of a recording of an advertisement produced with this technique. See .

I contacted Art Winfree's children, and they reported back that I was the second person this year to request this tape. Unfortunately, they can’t find it.

I would love to show a video recorded with this technique. Would you know of any other resource that I can go to buy a VHS/ DVD of this effect?

Recently I learned that there were more recordings of commercials, including one in which Thunderbird redwine is poured into a glass that turns red (personal communication from Professor Von Campenhausen, a world expert on Benham’s disk).

Thanks in advance,

Henk Buisman

Readers: Can you help Henk with this request? Please place "Backscatter" in the subject line of your e-mail. Editor.

The Scientific Exploration Society

Editor,

For those members who like both science and off-beat travel, the following link might be of interest: http://www.ses-explore.org/

It points to the home page of an organization that I only recently found out about, the Scientific Exploration Society.

Brian Chapel
Victoria, BC

A Remarkable Science Museum

Editor,

While visiting the spectacular new bridge designed by Lord Norman Foster, I came across a sign: MICROPOLIS cité des insectes.

I took the exit and found a remarkable museum. See for yourself at MICROPOLIS.

Tom Gartner

Using LEDs to Measure Sunlight

Editor

I am looking for an LED to measure sunlight at about 470 nm. Would a Radio Shack 500 nm LED work best or is there a better option? I could use a 468 nm LED as a source light and test various LED's against it. The LED with the highest voltage would be close. Since many white LEDs emit at 450 nm - 470 nm perhaps they might also be considered. I'm just trying to find a simple low cost method of measuring sunlight at about 460 - 470 nm.

As I cannot seem to find this information published anywhere, a note in "Backscatter" may be helpful to others as well.

Tom Teresa

Gallium nitride blue LEDs detect light with a sharp spike at about 373 nm and a broad shoulder out to about 400 nm. Various chemistries are used for 500 nm LEDs. A GaAsP-type green LED detects with a peak of about 525 nm. Gallium nitride green LEDs peak below that, but I've not measured them. Most white LEDs are blue LEDs coated with a phosphor. They will detect light at the same wavelength band as a blue LED but with less signal due to the phosphor coating. Some white LEDs use blue, green and red LED chips on a common substrate. The individual LEDs can be used to detect various wavelengths of light, and I built a shirt-pocket sun photometer based on this idea in 1992.

Some of my Radio Shack books and various scientific papers discuss the use of various kinds of visible and near-infrared LEDs as detectors, including:

F. M. Mims III, Sun Photometer with Light-Emitting Diodes as Spectrally Selective Detectors, Applied Optics, 31, 33, 6965-6967, 1992.

F. M. Mims III, An Inexpensive and Accurate Student Sun Photometer with Light-Emitting Diodes as Spectrally Selective Detectors, Proceedings of the Third Annual GLOBE Conference, 232-239, August 1998.

F. M. Mims III, and David R. Brooks, Sampling strategies for the GLOBE Sun photometer network, Proceedings of the Fourth Annual GLOBE Conference, University of New Hampshire, July 1999 (www.globe.gov).

Brooks, D.R., F.M. Mims III, G.Strachan, S.Kim, J.Yeung, B.N.Holben, and A.Smirnov, Calibrating the GLOBE sun photometer, AGU Spring Meeting, Boston, MA, May 31-June 4, 1999.

F. M. Mims III, An International Haze-Monitoring Network for Students, Bulletin of the American Meteorological Society 80, 1421-1431, 1999 (cover article).

F. M. Mims III, Solar Radiometer with Light-Emitting Diodes as Spectrally-Selective Detectors, Optics and Photonics News 11, 3-4, 2000.David R. Brooks and Forrest M. Mims III, Development of an inexpensive handheld LED-based Sun photometer for the GLOBE program, J. Geophysical Research 106, 4733-4740, 2001.

F. M. Mims III, An inexpensive and stable LED Sun photometer for measuring the water vapor column over South Texas from 1990 to 2001, Geophysical Research Letters 29, 20-1 to 20-4, 2002.

Forrest M. Mims III and David Brooks, Validation of remote-sensing satellites using inexpensive, ground-based instruments (GLOBE Annual Meeting, July 2002).

F. M. Mims III, Five years of photosynthetic radiation measurements using a new kind of LED sensor, Photochemistry and Photobiology 77, 30-33, 2003.

Editor.

Letters to "Backscatter" are welcome. Letters are subject to light editing to correct punctuation, spelling and grammar. By placing "Backscatter" in the subject line, you give us permission to consider publishing your letter. Send your letter to Backscatter.