Latent Image formation made apparent by double
decomposition with AgNO(3) and ordinary development has
been studied In thallous bromide-gelatin systems. The
plates prepared were found to be much faster than
those previously made(11), relatively stable latent
Image formation and no reduction in capacity for such
formation with time being features noted. The type of
gelatin used was found to be largely responsible for
the speed Increases.
The speed of the emulsion was found to be
increased by large amounts of bromine acceptors, but
small amounts apparently had little effect. Contrary
to previous work (11), the presence of Iodide In
Increasing amounts decreased the sensitivity of the
plate to blue light.
The thallous bromide plates were found to be
directly sensitive to green light. Reversal was found
to take place with red,green and low intensity blue
light, but In the case of the blue light such reversals
were only found at much higher primary densities and
lower intensity values than In previous work. The
straight line relation between the bleaching limit and
the primary density was confirmed, A general
desensitisation effect was found when malachite green
and and methylene blue were aided to finished emulsions
and an increase of the intensity of light at which the
bleaching limit occurred, was observed.
A study was made of the latent image distribution
in thallous bromide grains, using dichromate bleachers,
surface and total developers, and another reversal
effect was observed, which was dependent on the Internal
The Gurney-Mott mechanism of latent image
formation is considered to be applicable in general to
the thallous bromide system. An approximate general
equation was extended and developed.
Finally, some preliminary work was done on the
possible latent image formation in lead bromide,
antimony oxybromide and bismuth oxybromide. In the
last case latent image fomation was shown to be
present but was capable of development to a much
smaller extent than in the thallous bromide system.