Abstract: The problem how to raise the isoelectric point and salt effect of modified gelatin for coagulating emulsions of ammonical metnod has been attracting the attention of gelatin researchers. The present study is devoted to the following items:1) Synthesis of different modified gelatin with higher isoelectric point and better salt effect.2) Substitution degree evaluation.3) Iso-electric point determination with iso-electric focusing method.4) Coagulating and re-dispersing performances.5) Evaluation of recovery of silver halide and gelatin after coagulating.6) Sensitometric characteristics of emulsions prepared with GGC modified gelatin.Being as a coagulating agent of emulsion of ammonical method, GGC gelatin is superior to PA gelatin due to much less amount of acid required to start coagulation and higher sensitivity of the emulsion.

Key words: coagulating agent, modified gelatin, emulsion preparation