Wednesday, July 15, 2009

He Watches Over Us

First a few words about spectroscopy. That link has a cool animation of what looks like Pink Floyd’s Dark Side Of The Moon album cover where a prism splits a beam of white light into the colors of the rainbow--the spectrum (pl = spectra) of white light.
Early chemists used colored lines in spectra for the identification of materials when placed in flames.* The flame spectra of individual elements lack the full spectrum of the sun, and more or less resemble a bar code, that is, the spectra have one or several discrete lines separated by spaces. The discrete lines are a “fingerprint” or spectroscopic signature, unique for each element. With that brief introduction, we go back in time to 1868:
On 18 August 1868, a total eclipse of the sun was visible in India, and a number of scientists went there to make observations of the solar prominences. One who examined photographs of the spectra was Joseph Norman Lockyer (1836-1920) who although a civil servant at the War Office had already in his spare time done valuable work in astronomical spectroscopy.
Lockyer was particularly interested in a so called D3 line in the yellow region of solar spectra that had been obtained during the eclipse in India. It was known that the well-known sodium D line was in fact two lines close together, called the D1 and D2 lines. The D3 line could not be obtained from any substance in the laboratory, and Lockyer boldly suggested that it was caused by a new element, found in the sun but apparently not on earth. He gave this new element the name helium, from the Greek helios, the sun.
~The World Of Physical Chemistry, Keith J. Laidler
Lockyer’s hypothesis illustrates one of two ways to advance a theory in science: The first is to amass so much data that the subsequent explanation almost sounds obvious; the second is to boldly assert something with little or no support, and await experimental confirmation.

Helium is the second most abundant element in the universe after hydrogen. Where it does occur naturally on earth, it originates from the radioactive decay of heavier elements. The bulk of our domestic helium supply comes from deposits underground found with gas and oil. Helium is a non-renewable resource: even if made synthetically using radio-decay processes, the supply could not meet demand: link. We recognize helium's use in filling balloons but it is also used in welding and to replace nitrogen in synthetic breathing gas for deep-water diving because its lower solubility in blood minimizes occurrence of the often fatal "bends." However, its greatest use is in liquefied form to cool instruments and for cryogenic research. I used to use lots of it to cool the NMR supercon magnets found associated with nearly every modern chemistry lab.

Helium sits atop the northeast corner of the Periodic Table. From that vantage point, it is possible to look downwards through the eastern border of the chart all the way to the bottom. The elements directly beneath He are the so-called noble or inert elements on account of their general failure to interact chemically with other elements. The other related elements were all given Greek names: Neon (new), Argon (inert) Krypton (hidden), Xenon (strange), and Radon (named after radium but with its suffix changed to conform to the others). The discovery of the noble elements at first confounded the construction of the table--was there another family further to the right? But it was eventually recognized that the noble gas family perfected an understanding of the physical nature of the elements (more on that when we get to Lithium next).

So how many helium balloons would it take to lift a man? Mythbusters apparently did this experiment (I didn’t see it) with helium weather balloons and used about 45 of them, and their balloons were 2.5 meters diameter. I once tried to fill one of those inflatable love dolls (a gag gift) with helium to get it to float for a Halloween party- it didn't work. :(
*Robert Bunsen was a 19th century German chemist interested in the flame emission spectra of the elements--guess what he invented?


  1. Imagine constructing the periodic table, or predicting the existence of missing elements. The natural world is wonderful. I have really been digging on the general theory of relativity this year. I can't do the math, but there is an excellent discussion in a book called On The Shoulders Of Giants by Hawking. The gigabytes of brain covered there awe me.

  2. @dr. kill: The element technetium was "found" at least a couple of times, named various things before being prepared synthetically (hence the name that stuck).
    The early history of the chart is fascinating. The Russian chemist Dmitri Mendeleev (1834-1907) rightly deserves the credit, although a German chemist, Lothar Meyer worked out essentially the same system almost simultaneously, rather like Newton and Leibnitz with calculus.

  3. It's neat to me that in the fullness of time, scientific truth was revealed almost simultaneously. Are there other examples of this?

  4. @Ruth Anne: Off the top of my head: The discovery and proof that HIV is viral (Gallo vs Montaigne) is the most recent. Independent discovery is much more common. First to discover is analogous to first to invent and depends on who took and kept the best records. The US Patent office has procedures and protocols in place to determine first to invent in cases of competing claims. It's relatively rare, but it does occur.

  5. RAA- read about the way people have predicted the existence of unseen mass (planets, galaxies) from observing known orbits and gravitational effects. Also Einstein calculating to the second (1/3600 of a degree) how the mass gravity of the sun would bend light.

    Astrophysics, quantum mechanics- some smart people do this math

    Imagine simply measuring something affects the physics.

  6. Dude I didn't know you were like Mr Science and that. Cool.

  7. So since you know about science and all that how much helium does it take to fill up those gasbags on the Judciary commitee?

  8. Troop-this series is kind of a "Remembrance of Thing Pabst" for me.

    The trouble with those bilious windbags is gas blowby. They are never filled because they've always got it coming out both ends of their alimentary canals. Of course, this doesn't apply to my Congressaman Darrell Issa, who really should run for Senate or CA governor.

  9. I love helium. Is there any other element that people like to play with?

  10. I used to play around with mercury both when it was more common and also in the lab. We had this cool apparatus call a Toepler pump which is essentially a glass-contained mercury piston pump. I used it to collect and measure non-condensible gases.

    Xenon is another hoot. You can fill a balloon with the stuff and it looks normal but when you toss it to a friend it has obvious heft.

    The other day I tweeted a link about that Michigan teenager David Hahn who collected elements, including the radioactive ones. Link.

  11. We have a once a month use for liquid Nitrogen, and when the kids were young, no element was more interesting.

    Very cheap entertainment.