Natrium Facit Saltus

Metallic sodium is hot stuff.  It's sold in chunks or slabs immersed in oil to protect it from air and moisture.  I used to play around with it in the lab. I'd cut up chunks with a spatula (butter knife) and weigh it out for various uses.  It was always fun to toss any excess into a bucket of water and watch it sputter and bluster, forming itself into a smaller and smaller ball as it skittered across the surface, held aloft by the hydrogen gas it was forming. Sometimes it would even catch fire.  Here is a video showing this: link.

The thing about sodium is that it is so ubiquitous.  Universally, not just terrestrially. Unlike plants, we humans need sodium, yet nowhere near as much as we get. The whole "salt" debate is controversial. For leading links, check out the comment section in the following link.

Lesser known about sodium is that it gives us a pretty peach color which we associate with fire. But not the fire of the sun.  The orange blaze of the sun is really white light filtered by our atmosphere and lacks the orange color of sodium. Let me explain.

The sun floods us with a spectrum of visible light.  Here is the solar spectrum sorted according to ROY G. BIV wavelength:

Missing from the solar spectrum are several well known "lines" having alphabetical designations. These Fraunhofer lines were discovered in the 19th century by early German spectroscopists who first analyzed sunlight.  The black bands are "missing" wavelengths caused by the absorption of those colors by different chemical elements present in the outermost regions of the sun. Sodium in the sun causes the pair of lines labeled "D" in the solar spectrum. We don't notice that the lines or specific colors are missing from sunlight because our eyes aren't able to distinguish a missing wavelength, especially when surrounded by others (especially ones close in wavelength).

Here on earth, sodium in flames gives an intense orange glow which is the exact color missing from sunlight. Try sprinkling a little salt on an open flame sometime--you should see an intense light that looks like this:

The sodium spectrum above reminds me of an old-fashioned AM/FM radio dial found in 20th century automobiles and stereo systems. Sheesh I'm getting old fast.
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When I was researching this blog post, I kept running across articles which ascribed the color of campfires and the like to the intense color of sodium. I thought this was odd because plants for the most part do not require sodium, so any sodium present in wood must be adventitious and probably sequestered away.  It turns out that the common orange color seen in burning wood is partially due to residual sodium, but mostly comes from luminescent soot particles, a phenomenon first explained by Michael Faraday (link).