The Bunsen-Kirchhoff Spectroscope.
A short time ago, while walking through the rows of stalls at the Arezzo antiques fair, held every first Sunday of the month, I noticed on the table of one of the many stalls, the barely perceptible golden reflection of a Bunsen spectroscope, almost submerged by knick-knacks of every kind. It was a long and tiring negotiation to get a reasonable price.
It is disconcerting how an object, for a highly symbolic chemist, can be found lost among “superfluous” things. The name of the manufacturer and the place are engraved on its surface: “A. Krauss – Hamburg”
The date of manufacture is not reported. But I discovered that a spectroscope of the same generation, completely similar, is preserved in the Physics Museum of the University of Rome. The latter was purchased in 1887 by the Royal Physical Institute of via Panisperna, where Enrico Fermi worked. It is therefore a spectroscope intended for research.
Il primo spettroscopio
Il primo Spettroscopio ideato da Bunsen e Kirchhoff risale al 1859-60.
It is described in an article published in the journal Annalen der Physik und der Chemie entitled “Chemical Analysis by Observation of Spectra” by Gustav Kirchhoff and Robert Bunsen:
The second version of the spectroscope
The spectroscope found at the Antiques Fair is precisely the model that Bunsen and Kirchhoff obtained with the improvements made to the first version.
The first model of spectroscope was modified by Bunsen and Kirchhoff with some improvements. The small telescope separate from the rest of the spectroscope, used for the orientation of the prism and the graduated scale, now constitutes a third arm D fixed in the body of the spectroscope. It has a lens at one end and at the other a reference scale for the wavelengths (generally engraved on a glass plate) which, when suitably illuminated, superimposes its image on that of the spectrum being examined. The telescope C, containing the observation optics, is equipped with a gear system (with micrometric screw) that allows the mutual angle of collimator B and telescope to be varied for the resolution of the different spectral lines. Next to the slit (the opening of which is adjustable by means of a micrometric screw), there is a small prism, used for the direct comparison between a reference spectrum and the spectrum under study (this element is missing in the spectroscope, it is visible in the image of the spectroscope in the Pisa museum). This was achieved by covering half of the slit with this prism, and making light from a source (a small Bunsen burner) placed on the side of the collimator A fall on it. In this way, the spectrum produced by the additional prism was superimposed on that due to the main prism, thus allowing a simultaneous study of the two spectra.
After a few years this instrument will spread in the chemistry and physics laboratories of Europe marketed by the company of A. Krüss Optronic, one of the oldest and most prestigious German industries in the field of optical instruments, founded in 1798 with headquarters in Hamburg, still operating.
The spectroscope found at the Arezzo Antiques Fair is thus added, as I reported some time ago in a post always in this blog, to the complete Encyclopedia of Prof. Francesco Selmi of 1870 and to the collection of lessons of General Chemistry of Prof. Gioacchino Taddei of 1850.
What will be the next discovery?
