Phosphorescence of mercury vapour after removal of the exciting light

Abstract

By means of Becquerel’s phosphoroscope the fluorescence of solids has been shown to be persistent, but up to the present phosphorescence in the case of liquids and gases has not been observed. That of solids has generally been explained as due to chemical reactions brought about by impurities, while in the case of gases it has been considered that damped vibrations of the rapidity of those connected with light could not be conceived as persisting for a sufficiently long time for the necessary observations to be made. On the other hand, because of their relative simplicity, gases and vapours have been recognised as being eminently suitable for the study of fluorescence and kindred phenomena. Wood has applied the phosphoroscope to the case of sodium vapour, with however a negative result. In the present experiment I have attacked the problem in a different way. The method used was to pass a beam of the exciting light transversely across a rapidly moving column of mercury vapour, obtained by distillation in vacuo . Then if the fluorescence of the vapour persists the luminosity should be carried along with the stream. The fluorescence was excited by 2536 light which was obtained by means of a quartz mercury lamp. Under suitable conditions the vapour could be seen to be still fluorescing, after it had passed a distance of some 18 inches from the point of excitation.