Phosphorescence of Photographic Plates

Abstract

SOME time ago when developing an X-ray photograph I observed the effect noticed by your correspondent in your last issue. Very little of the silver salt had been affected, and the plate, after development, when put into alum solution lit up as described. I have often watched for the same effect since with ordinary negatives; sometimes there is phosphorescence, sometimes not. Apparently a fairly long development with the pyro soda is necessary. Not only the plate itself, but the used developer will give the phosphorescence with alum solution. Dilute sulphuric acid may be used instead of the alum. Quinine sulphate or hydrochloride does not light up when the used developer is added, but will do so if a few drops of sulphuric acid are subsequently introduced. Printing out paper may sometimes be successfully used instead of the plate, or the experiment may be still more easily made by mixing potassium bromide and silver nitrate solutions, in dim, gaslight, decanting, and shaking up the resulting silver bromide with pyro soda. A red liquid results which gives the lighting up effect when poured into alum solution or dilute sulphuric acid.