INTENSIFICATION AND REDUCTION 557 



Farmer's double-solution reducer is made up as two stock solutions, according to 

 the formula: 



Solution 1 



Potassium ferricyanide 7 . 5 g. 1 oz. 



Water to make 1 1. 1 gal. 



Solution 2 



Sodium thiosulphate fhypo) 200 g. i lb. 11 oz. 



Water to make 1 1. 1 gal. 



The negatives are agitated in solution 1 for from 1 to 4 min. (depending upon 

 the reduction desired) at 65 to 70°F. The film is then immersed in solution 2 for 

 5 min., after which it is washed thoroughly. If more reduction is desired, the process 

 may be repeated. 



Haddon's Reducer. — A single solution made of ferricyanide and ammonium sulpho- 

 cyanide, formulated by Haddon, is of the subtractive type but has the advantage that 

 the solution is stable. The reducing solution is made as follows: 



Potassium ferricyanide 5 g. 22 gr. 



Ammonium sulphocyanide 10 g. 44 gr. 



Water to make 11. 10 oz. 



The negative is immersed in this solution until the desired reduction is obtained, 

 after which the film is washed in running water and dried. With this reducer, there 

 is a tendency for a slight white deposit to form on the film. The deposit is soluble in 

 sodium thiosulphate as well as in sodium cyanide and may be removed by immersing 

 the negative in hypo. A small quantity of sodium cyanide may be added to the 

 reducer to prevent formation of this deposit. 



Iodine-cyanide Reducer. — A subtractive reducer which removes a slightly greater 

 quantity of silver from the denser portion than from the lower densities may be made 

 of a dilute solution of sodium or potassium cyanide with a small amount of iodine. 

 A suitable formula is 



Sodium cyanide (poison) 5 g. 22 gr. 



Iodine crystals 1 g. 4 . ,5 gr. 



Water to make 11. 10 oz. 



The solution is highly unstable and must therefore be prepared immediately before 

 use. Approximately 30 per cent reduction in density may be obtained in 10 min. 

 After suitable reduction has been obtained, wash in clear water, and dry. 



Ferricyanide and Cyanide Reducer. — A solution of potassium ferricyanide and 

 sodium cyanide forms a stable reducer of the subtractive type. Its disadvantages 

 are that it is highly poisonous and softens the gelatin, so that preliminary hardening 

 in a formalin bath (see Chapter on Fixing, Washing, and Drying) is necessary. A 

 suitable formula is: 



Potassium ferricyanide 2 . 5 g. 10 . 5 gr. 



Sodium cyanide 2..5 g. 10.5 gr. 



Water to make 1 1. 10 oz. 



By doubling the concentration of the ingredients, a more rapid rate of reduction 

 is obtainable. After the desired reduction, wash the negative in water, and dry. 



Modified Belitzski's Reducer. — This reducer partakes of the characteristics of both 

 subtractive and proportional reducers. It reduces the slope of the Z)-logio E curve of 

 the photographic material, although a greater proportion of silver is removed from 

 the lower than from the higher densities. The solution keeps from 3 to 5 days. The 

 modification recommended by Crabtree and Muehler is 



