In order to obtain an appreciable amount of ultraviolet radiation it is necessary to heat the radiating substance to a high temperature, 3,000 C. (5,400 F.) or higher. Since solids ( e. g., metals such as tungsten) evaporate very rapidly at high temperatures, sources of ultraviolet radiation are practically confined to electric arcs between electrodes of metals, of carbon and of mercury vapor in a closed tube of quartz glass called "the burner."
The amount of ultraviolet radiation emitted by the bunsen gas flame, either with or without an incandescent mantle, is not sufficient to warrant its consideration as a therapeutic agent.
In this paper the wavelength scale used is the millimicron (mμ), which is equivalent to 10 angstrom units. Thus the ultraviolet emission line of the quartz mercury vapor arc lamp, frequently mentioned in paper, is 302 millimicrons (3,020 angstrom units). More complete data on the radiation from arc lamps1 and on