A sealed glass artifact consisting primarily of two horizontal elements that are joined at either end. The enclosure contains a significant amount of liquid mercury, the majority of which is pooled in lobes located at the end of each horizontal element. Connected to each lobe is a metal terminal through which an electrical current is passed through the liquid mercury.
Within each lobe is an inner “finger”. These are connected to each other by a tubular channel. At each side of this connection is an outlet that is connected to an external water supply. This forms a cooling circuit with water flowing through the fingers within mercury bulbs and back to the water supply.
This artifact was acquired with an annotated rolled printout of the Raman spectrum of C10H10 in a resealable bag.
Note that this artifact is photographed on a foam cradle that was made after it was acquired by the collection.
Accession Number: 2024.ph.886
Alternative Name:
Primary Materials: Glass, Mercury
Markings:
Dimensions (cm): Height = 25; Width = 15; Length = 35.
The Toronto Lamp is a high-power light source. It is a low-pressure mercury lamp, a form of gas discharge lamp, that was designed to provide a monochromatic source of light suitable for Raman spectroscopy. This is achieved by isolating the powerful 4358A peak in the spectrum of incandescent mercury using a filter typically consisting of a solution of sodium nitrite.
The lamp consists of two pools of mercury housed in separate electrodes. After the lamp started using a handheld Tesla coil, a current of around 15 to 20 amperes is passed across the electrodes causing an arc to form through the mercury vapour.
The electrodes are cooled by a flow of water through “fingers” projecting through the liquid phase, into the gaseous phase of each electrode. Cooling permitted the use of higher currents which increased the spectral line intensities relative to the background. The lamp could be operated over very long periods without any noticeable reduction in the spectral lines [Welsh et al, 1952]. In a typical experimental arrangement, several lamps illuminated the sample-containing Raman tube, forming a “Raman excitation unit” [Woodward et al. 1957, 222].
The Toronto Lamp was superseded as a monochromatic light source by the development of lasers in the 1960s.
The artifact is intact and in good condition. It was removed from its original metal housing, which was bulky and heavily corroded at its base from having been partially submerged in a tank of cooling water. The water inlet and outlet are discoloured where they were connected to rubber tubing. The electrical connections are slightly oxidized.
Associated Instruments:
Department of Physics, University of Toronto (Likely by glassblower Reuben H. Chappell)
Date of Manufacture: c. 1950s.
The early provenance of this particular artifact is unclear. It was used for some time in the from the University of Toronto Department of Physics undergraduate teaching laboratory in a teaching experiment involving Raman Spectroscopy. This lamp was decommissioned around 2019. It was replaced in the Raman teaching experiment with a more efficient laser diode.
This artifact was acquired from the University of Toronto, Department of Physics undergraduate teaching laboratory on February 27, 2024.
J. J. Heigl, B.F. Dudenbostel Jr., J.F. Black, and J.A. Wilson (1950) “Direct-Recording Raman Spectrometer.” Analytical Chemistry 22 (1), 154-159.
H. L. Welsh, M. F Crawford, T. R Thomas, and G. R Love (1952) “Raman Spectroscopy of Low Pressure Gases and Vapors.” Canadian Journal of Physics 30, no. 5: 577–96.
J. W. Kemp, J. L. Jones, and R. W. Durkee (1952) “A Source Unit for Raman Spectroscopy.” Journal of the Optical Society of America 42, no. 1: 811-814.
Boris P. Stoicheff (1954) “High Resolution Raman Spectroscopy of Gases: I. Experimental Methods.” Canadian Journal of Physics 32, no. 5: 330–38.
L. A. Woodward, and D N Waters (1857) “A Water-Cooled Mercury Arc Lamp for the Excitation of Raman Spectra.” Journal of Scientific Instruments 34, no. 6: 222–24.
Henry M. van Driel (2018) “Boris Peter Stoicheff: 1 June 1924 — 15 April 2010.” Biographical Memoirs of Fellows of the Royal Society 66: 403–22.
The Raman effect was first discovered by Indian physicist C. V. Raman (1888- 1970) in February of 1928. Involves a scattering process that affects a very small portion of the incoming light. This scattered light provides clues to the molecular bonds of a material. Following its discovery, Raman Spectroscopy provided an important analytical tool for molecular research in physics and chemistry.
Due to the weakness of the Raman effect, recording the Raman spectrum requires a sample material to be exposed to a powerful source of monochromatic light over a long period.
The Toronto Lamp was developed beginning in the late 1940s by University of Toronto physicist Harry Lambert Welsh (1910-1984) and his collaborators to provide such a source. (See Welsh et al. 1952). This example differs from the lamp shown on p. 579 of Welsh et al. 1952 in that it does not feature separate starting electrodes, likely suggesting that it is a later model.
A report published by a group of researchers at Esso Laboratories, Standard Oil Development Company, Linden, Y. J, describes a helical-type Toronto lamp supplied by the Physics Department at the University of Toronto that was used for Raman analysis of hydrocarbon mixtures. This was found to be superior to the high pressure Model H-l arc lamp, manufactured by the General Electric Company . (See Heigl et al. 1950, 154-155).
Applied Research Laboratories, an American manufacturer of scientific equipment, produced this helical version of the “’Toronto’ type” lamp as part of a commercial system for Raman spectroscopy. (See Kemp, Jones, and Durkee 1952.)
This raises the question of whether the non-helical version of the lamp, described in Welsh et al. 1952 and shown in this entry, is a later or concurrent design relative to the helical unit supplied by the Department of Physics to Esso in 1950. No doubt, the non-helical version would have been easier for a glassblower to fabricate.
A paper published in 1954 by University of Toronto physicist Boris Stoicheff shows a much different version of the Toronto lamp, over one meter in length, with a water cooling shroud covering nearly its entire surface. However, Stoicheff cites Welsh et al. 1952 and notes that “Recently, Crawford, Welsh, and Harrold were able to increase the intensity in this type of lamp by means of a water-cooled pyrex tube placed within the discharge tube itself.” This suggests that the lamp shown in the Stoicheff paper may have been an earlier design. (see Stoicheff 1954, 334-335)
A research group at the Inorganic Chemistry Laboratory, University of Oxford, noted the following in 1957:
“A notable advance was the development of the so-called Toronto arcs with water-cooled mercury pool electrodes. These lamps give a much “cleaner” and more satisfactory spectrum, in that the cooling keeps the mercury vapour pressure low and so reduces the intensity of the otherwise troublesome continuous spectrum. A further advantage is that the intensity of the blue line (4358 A) relative to its weaker close companions is much enhanced.”
This paper describes an alternative, more compact, version of the Toronto arc that permitted more lamps to be be used in an experiment. (See Woodward et al. 1957).
The Toronto Lamp is notable for its place in the early career of celebrated Canadian physicist Boris P. Stoicheff (1924 – 2010). Stoicheff used the lamp in his early spectroscopic investigations at the University of Toronto Department of Physics. Late in 1960, Stoicheff and Gary Hanes built the first operational laser in Canada for use in their spectroscopic research. (See van Driel 2018).
The laser would replace the Toronto lamp as a light source for Raman spectroscopy. Disadvantages of the Toronto lamp included high voltage and current (120V DC/ 20A when used in the undergraduate teaching lab), the need for water cooling, a loud buzzing sound when in operation, and very high emission of UV light.
- Donated to UTSIC