A water-cooled mercury arc lamp for the excitation of Raman spectra

Abstract

A modified Toronto-type mercury vapour lamp, suitable for the excitation of Raman spectra, is described. It is constructed throughout of Pyrex and is water cooled, not only at the electrodes, but also along the whole length of the arc (approximately 185 cm). An inverted-U shape is adopted, so as to allow free expansion of the inner arc tube relative to the cooling jacket and thus render expansion bellows unnecessary. Current-voltage characteristics are given for the range 10-32 A. The intensity of emission of each of the mercury lines 4046, 4358 and 5461 A is determined by photographic spectrophotometry as a function of lamp current or wattage. For a given current the light output is found to be slightly lower when the lamp is running with full cooling than when it is running as an ordinary Toronto arc with cooling of the electrodes only; but with full cooling higher currents can be used and thus greater light outputs attained. However, the rate of increase of intensity with increase of current is found to fall off at higher values; so that, for a given wattage, a single lamp gives less light than several in parallel.