617,720. Photographic silver salt emulsions; photographic developers. KODAK, Ltd. (Eastman Kodak Co., Smith, W. F., and Stauffer, R. E.). March 21, 1944, No. 31524/46. Divided out of 598,166. [Class 98 (ii)] The speed or contrast or both of a silver salt emulsion sensitized with a cyanine or carbocyanine dye having its maximum sensitizing effect within the wavelength range of visible light is increased by development under alkaline conditions in the presence of a substance of the formula R-NH-NH2, wherein R represents hydrogen or an esterified acid, aryl or heterocyclic group, or a group of the formula R<1>-NH-CO-, wherein R<1> is H, substituted or unsubstituted amino, aryl, or a carboxylic acid amido group. The emulsion may be developed at a pH value of at least 9.5, and the substance and the dye may be in the emulsion or the developer. The substance may be water-soluble or -insoluble, and may be a hydrazine such as hydrazine itself, a semicarbazide, carbohydrazide or aminobiuret, a hydrazone. Metol, catechol, hydroquinone and pyrogallol developers are referred to, and formulae are given for a hydroquinone sodium hydroxide developer of pH 12.8 and a metolhydroquinone developer of pH 10.2. A metolhydroquinone developer of pH 9.7 contains hydrazine dihydrochloride and 6-nitrobenzimidazole nitrate. Hydrazines referred to are hydrazine dihydrochloride and hydrate, ethyl hydrazine carbonate, 2-benzthiazolylhydrazine, 2-quinolylhydrazine, 4-hydrazinoquinaldine, 2- pyridylhydrazine, p - hydroxyphenylhydrazine hydrochloride, 2 : 4 - dinitrophenyihydrazine and p - nitrophenythydrazine hydrochloride. Other hydrazine compounds referred to are semicarbazide and carbohydrazide hydrochlorides, acetcarbohydrazide pyridinium chloride, malonyl dicarbohydrazido - pyri - dinium bromide, 4 - phenylsemicarbazide, 4- (p - chlorophenyl) - semicarbazide, 4 - (o - tolyl)- semicarbazide, 4-(4<1>-chloro-2<1>-methylphenyl)- semicarbazide, diaminobiuret and aminobiuret. Dyes referred to are 3: 3<1>-diethylthiazolinocarbocyanine iodide, 3 : 3<1>- diethyl - 9 - methyl - selenacarbocyanine iodide, 3 : 3<1> - diethyloxa - carbocyanine iodide, 3 : 3<1>-diethyloxacyanine iodide, 3 : 3<1> - dimethyl - 9 - ethyl - 4: 5: 41: 5<1> - dibenzthiacarbocyanine bromide, 3: 3'-diethylthiacarbocyanine iodide, 3: 3<1>-diethyl-9-methylthiacarbocyanine iodide, 3 : 3<1> - diethyl - 41- methyloxathiazolocarbocyanine iodide, 1:1'- diethyl-2: 21-cyanine iodide, and (3-ethyl-2- benzoxazole)-(1-ethyl-2 : 5-dimethyl-3-pyrrole)- dimethinecyanine chloride. If the hydrazine or the dye is added to the emulsion, the silver ion concentration of the latter should be high. Carbonyl hardening agents should not be added to the emulsion, but chrome alum may be used. An emulsion binder other than gelatin may be used. High-contrast emulsions are satisfactory. In example (1), the speed, contrast and fog of four portions of a gelatino silver bromiodide emulsion exposed through a filter absorbing green light and developed in a developer comprising hydroquinone and sodium hydroxide are compared, one portion of the emulsion being plain, one containing hydrazine dihydrochloride, another 3 : 3<1> - diethylthiazolinocarbocyanine iodide, and the fourth both hydrazine dihydrochloride and 3 : 3<1> - diethylthiazolinocarbo - cyanine iodide. In example (2), a similar comparison is made for four portions of a silver chlorobromide emulsion, the compounds being 4 - (o - tolyl) - semicarbazide and 3 : 3<1> - diethyl - thiazolinocarbocyanine iodide. In example (3), the comparison is made using the compounds malonic acid dicarbohydrazido pyridinium bromide and 3: 3<1>-diethyl-9-methylthiacarbocyanine iodide. In example (4), a comparison is made for the development of a chlorobromide emulsion containing 4-(o-tolyl)-semicarbazide in a plain developer and in a developer containing 3: 3<1>- diethylthiazolinocarbocyanine iodide. In example (5), a comparison is made for the development of a chlorobromide emulsion in a plain developer, in a developer containing hydrazine dihydrochloride, and in two developers containing the same quantity of hydrazine dihydrochloride, but different quantities of 3 : 3<1> - diethylthiazolinocarbocyanine iodide.