Effects of Irradiation of Crude Coal Tar by Quartz Mercury Vapor Lamps. I. Evidence of chemical changes as shown by changes in absorption spectra.

Abstract

The stimulus to investigations on the possible changes in the absorption of crude coal tar when irradiated by air-cooled quartz mercury vapor lamps was furnished by the fact that a simple but apparently beneficial treatment for psoriasis consists in irradiating, with sources rich in ultraviolet light, affected areas which are covered with a thin film of crude coal tar ointment. 1 Neither the ointment nor irradiation alone produces as marked results; hence the combination of the 2 is used simultaneously. The so-called crude coal tar ointment is made up of 2 drams each of crude coal tar and pulverized zinc oxide mixed with 2 ounces each of corn starch and petrolatum.

It seemed highly probable that the only substance in this ointment which might give evidence of chemical change under ultraviolet irradiation was the crude coal tar and that, by investigations of a spectroscopic character, it might be possible to determine which portion of the crude coal tar was the active or stimulating agent. Thus far we have settled definitely only the question relative to changes in absorption spectra produced by irradiation with an aircooled quartz mercury vapor lamp. The lamp used was made by the Victor X-Ray Corporation and was operated at 90 volts at a distance of 17 cm.

The apparatus for obtaining absorption spectra is shown in Fig. 1. A 0.5 kilowatt transformer is used for electrical excitation together with a suitable condenser which is joined in parallel (multiple) with a spark-gap consisting of one electrode of aluminum and one of nickel separated by a few millimeters. The photographic plates used for obtaining the spectrograms were made more sensitive to the extreme ultraviolet irradiation by treatment with oil. In the development of the plate the oil is carefully removed with anhydrous ether before it is immersed in the developer. Of the various possible solvents for crude coal tar, ether was chosen because it is least opaque to the ultraviolet region and does not change appreciably (if at all) when exposed to prolonged irradiation.