Periodicity in the Solarisation of Calcite

Abstract

REPEATED solarisation due to a prolonged exposure to the light of a quartz mercury lamp was observed by the photoluminescence exhibited by calcite from Nabeto. A definite quantity (0.045 gm.) of the finely granulated specimen was put at suitable intervals of time into the depressions of the sample holder1 placed 15 cm. underneath the lighted lamp (100 volts, 3.1 amp.) which was employed as a constant source of exciting light. Thus a set of samples was subjected to excitation. A panchromatic plate was then applied, immediately after cessation of excitation, on the sample holder, thus charged with a set of the samples excited for discrete durations of time, the distance between the surface of samples and the photographic plate being 3 mm. After being left two hours, the plate was developed, and the photographic densities of the images generated on the plate by the action of phosphorescent light of the excited samples were determined by means of a microphotometer. The results are shown graphically in Fig. 1, which gives the growth curve of photoluminescence, indicating its periodic reversal under the exciting rays. The ordinates represent the density corresponding to the intensity of phosphorescence and the abscissae the duration of excitation.