Humboldt State University

Robert A. Paselk Scientific Instrument Museum

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Spectrometer

Wm. Gaertner & Co.

Humboldt S-T-C; c.1926

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Usage/History

The oldest optical method for chemical analysis, Bunsen and Kirchhoff introduced spectroscopy as a laboratory method in 1860. The basic features of the spectroscope (or spectrometer) include a slit and collimator to produce a parallel beam of light which then falls on the dispersive element (a prism or grating). The resulting spectrum is then observed through a telescope. Spectrometers are particularly valued in two types of studies: 1) The identitfication and quantification of elements by the observation of line spectra (emission or absorption), 2) The identification and quantification of substances by the observation of absorption bands.

In this spectrometer the prism table, the collimator, and the telescope positions may be determined relative to a graduated circle. This example is Gaertner's student instrument. It could be used for the determination and analysis of spectra using either a prism or grating. It could also be used in the measurement of angles between prism faces, the determination of angles of refraction and reflection etc. In another common type of instrument, the Bunsen Spectroscope, there is no graduated circle, instead measurements are made relative to a projected scale.
 
Some contemporary/early descriptions of the spectroscope and its use are provided below:

Description

Gaertner small model spectroscope. The graduated aluminum circle is 125mm dia, with divisions every 30' and two verniers reading to 1'. A black japanned brass plate protects the graduated circle, having oval cutouts at 180° for reading the verniers. The instrument is stamped on the plate in white filled letters: WM. GAERTNER & CO / CHICAGO / 323. The circle with the attached telescope and the vernier plate move independently, and are both equipped with clamp and tangent screws. The aluminum prism plate is 80mm dia, and is fitted with leveling screws and a clamp for the prism (missing). The telescope and collimator are each held in a cast iron double cradle by five adjusting screws: two near the objective provide a pivot, while the remaining three provide horizontal and vertical angular adjustment. The entire instrument sits on a substantial cat iron tripod. All adjusting screws are of polished nickel plated brass with checkered knurling. The telescope and collimator each have 25mm objectives and 160mm? focal length. The slit has nickel silver jaws, adjusted by a screw to the side (replacement). The telescope focuses by means of a knurled ring. The eyepiece is equipped with a beam splitter accessed through a hole to the right side for superimposing scales etc. on the spectral image. An oval brass tag, attached with brass pins to the opposite right of the collimator, is stamped: HUMBOLDT S-T-C / 2103.

Bibliolgraphy

Bennet, J. A. The Celebrated Phaenomena of Colours: the early history of the spectroscope. Whipple Museum of the History of Science, Cambridge (1984).

Brand, John C. D. Lines of Light: The Sources of Dispersive Spectroscopy, 1800-1930. Gordon and Breach Publishers (1995)

Minor, Ralph S., Physical Measurements, A Laboratory Manual in General Physics for Colleges: Part 2, Magnetism and Electricity, Sound and Light 3rd ed, Associated Student's Store, Berkeley (1956) pp. 118-121, 122-124, 158-159.

 


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Last modified 30 August 2010