re- S-nitroindazole, benzidine, mercaptans, etc. (see Meessented by the following general formula: fr R1 i v-* f R-N (--CH=CH) i-TSC H-=CH-C (20H- CID .i=l\|T-Ri The Theory of the Photographic Process, Macmillan wherein R and Ri each represents an alkyl group con- Pub., page 460), or mixtures thereof; hardeners, such as taining from 1 to 2 carbon atoms, R2 represents a monoformaldehyde (U. S. 1,76