Abstract: The effect of some photographic additives, such as potassium thiocyanate, ammonium thio-cyanate, thiourea and urea on the multiple structure formation of photographic gelatin was investigated by circular dichroism (CD) method. The experimental results showed that the above-mentioned additives have a very strong influence on the CD of photographic gelatin, but they differ from each other in extent and manner. In the case of potassium thiocyanate and urea, with the increase of their amount, CD value first deceases gradually, through a minimum, finally increases again. In the case of thiourea, with the increase in amount the CD value decreases very fast, and finally approaches zero. In contrary to thiourea, ammonium thiocyanate exhibits a monotomic increasing tendency of CD value. All these different effects were attributed to the two contradictory factors: one decreasing CD by the additives and the other increasing CD by foreign Cotton Effect.

Key words: photographic gelatin, additive, multiple structure, circular dichroism