🚀 go-pugleaf

   In response to Donald Simanek's questions about the electrocuted
pickle and the spectroscope we used, here's a little more information.
   We use inexpensive spectrscopes developed by Project Star that are
sold by Learning Technologies, Inc.  These have a holographic grating
equivalent to about 600 line/mm with a scale calibrated in nm and eV
that's visible when one looks in the spectroscope. The scale can be moved
back and forth a little bit for calibration, and a table of known
wavelengths is printed on the spectroscope for that purpose.  We use the
546 nm green line in the mercury spectrum from a fluorescent light as
a convenient calibration check.  I think the specified accuracy of the
spectroscopes is something like +/-5 nm, but with careful calibration
they are good to a couple of nm or better.  The Na doublet isn't resolved
but that's mainly due to the short optical length of the spectroscope
(about 25 cm).  The contrast of the gratings is very high, so even faint
lines can be seen fairly easily.  (The Fraunhofer lines in sunlight are
clearly visible when one observes the sky through the spectroscope.)
When students calibrate their spectroscope carefully, they usually find
a wavelength of 590 nm for the yellow light from a low pressure Na lamp.
   When we observe the glowing pickle, the perceived color is yellowish,
but not pure yellow.  Remember that the pickle itself is green, and that
affects the color of the light observed.  However, when the glow is
observed through the spectroscope, a line is clearly visible at 590 nm
(or whatever wavelength had previously been recorded for the Na D line),
so we can be reasonably sure the pickle contains Na.  Obviously, other
elements produce yellow light (for example, Hg has a yellow doublet at
577 and 579 nm, and these are clearly visible from a fluorescent lamp),
but it's unlikey that a pickle out of a jar will contain a significant
amount of Hg.  What I want the students to do is compare the pickle
spectrum to other spectra they have just observed and look for
similarities and differences.
   By the way, I was surprised when I described this part of the experiment
to the students to be told by one fellow that his uncle does this trick
every year for part of his New Year's Eve celebration.  (I wonder what
is the significance of electrocuting a pickle to welcome the new year.)
Also, one of my colleagues reported to me a couple of days ago that she
saw the electric pickle demonstration on an early-morning science show
on TV this past Saturday.

Steve Luzader
sluzader@fre.fsu.umd.edu