Among the gelatin hardness for photographic emulaion, the formaldehyde, dialdehydes, n-Methylol compounds, ketones, carbonylic acid and carbamic acid derivatives, and s-Triazine derivatives were studied The greater purts of hardeners formed cross-link by the reaction with E-Amino group in the lysine and OH group in the hydroxylysine. Glutaraldehyde produced most stable cross-link due to the formation of pyridinum ion. 2.5- hexanedione and 3-hexene-2,5-dione possible to use as the ketone hardner. The sodium salt of 2.4-dichloro-6-hydroxy-S-Triazine was newly developed as the olefinic hardners for emulsion.
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