Classic Kit has turned into something of an obsession – this is shown by the fact that this month is the 75th column in the series. Looking back at the early ones, I wish I could rewrite them and correct some of the omissions. This month gives me the opportunity to do just that as I finally decided to write about Robert Kirchoff and his spectroscope. It’s an opportunity to do slightly more justice to Robert Bunsen, whom I rather demeaned when I wrote, rather lazily in retrospect, about the Bunsen burner.
What I failed to do was to draw proper attention to Bunsen’s incredible contributions to chemistry, from his battery to his role in the development of spectroscopy and in the characterization of the rare earth elements (which you can find in my Terra Rara lecture from the Royal Institution).We have an old but solid spectroscope in our teaching lab – slit, prism, collimator lens etc that our students use. Although some look at it and think “relic” and ask why on earth we use something so old fashioned, the point is that it’s not a black box, unlike a typical UV/Vis spectrometer. You can see all the bits and follow the path of the light as it travels through the device and you get to actually see for yourself that the sodium D line is a doublet.
The device was not completely Kirchoff’s, of course, similar devices had been built before him. I’ve had to condense that part of the story down to just a list of names. But what is important is that it was Kirchoff, with the aid of Bunsen, who joined the dots and realized the true importance and utility of the device. In doing so, the two of them changed our world.
I give you Kirchoff’s spectroscope.
[I should mention that we also have an undergraduate experiment in which students construct a spectroscope from a cardboard box and a diffraction grating, using a helium spectrum to calibrate their scale and then use the device to measure Ryderberg's constant for hydrogen. It's a lovely, simple experiment and again it's a way of deconstructing scientific ideas by getting students to use almost improvised methods.]