Process for the preparation of octahedral silver chloride-containing emulsions

Claim 1

A process for preparing a radiation-sensitive photographic emulsion comprising bringing aqueous silver and chloride-containing halide salt solutions into contact in the presence of a dispersing medium thereby forming silver halide grains wherein at least 50% of the total grain population are octahedral silver halide grains and wherein the halide content of the silver halide emulsion is at least 50 mole percent chloride, based on the total moles of silver present, the improvement being forming the octahedral grains at a pH in the range of 2.5 to 9 and a pCl of 0 to 3 in the presence of a crystal habit modifying amount of an organic nitrogen-containing heterocyclic compound of the formula: ##STR2## wherein Z is C or N; R 1 , R 2 and R 3 , which may be the same or different, are H or alkyl of 1 to 5 carbon atoms; when Z is C, R 2 and R 3 when taken together can be --CR 4 ═CR 5 -- or --CR 4 ═N--, wherein R 4 and R 5 , which may be the same or different are H or alkyl of 1 to 5 carbon atoms, with the proviso that when R 2 and R 3 taken together is said --CR 4 ═N--, --CR 4 ═ must be joined to Z; and salts thereof, with the proviso that the organic nitrogen-containing heterocyclic compound is added after at least about 6.0% to about 45% of the silver salt solution has been added.