HADDON'S FORMULIE Many useful formulm due to A. Haddon are in use, three of the best known being given below : Reducer for Negatives and P.O.P.—This con sists of potassium ferricyanide and ammonium sulphocyanide, and is compounded as follows : For negatives— Potassium ferricyanide io grs. i i g.
Ammonium sulphocyanide 20 „ 22 „ Water . . . 2 OZ. 1,000 ccs.
This reducer has the merit of keeping well. The plate is immersed in the solution in the usual manner, rocked until reduction is sufficient, and then washed for ten minutes. A dry negative should be first soaked in water.
For P.O.P.
Potassium ferricyanide 4 grs. 4'4 g.
Ammonium sulphocyanide 20 „ 22 „ Water . . . . 2 oz. r,000 ccs.
Platinum Toning Bath for P.O.P.—This is a toning bath on the lines suggested by Henderson. The formula is : Platinum perchloride 15 grs. I g.
Sodium formate . 500 „ PP Water . . . 175 „ I I' 5 PP Formic acid . . 15o mins. 9 ccs.
Before treatment, the prints must be washed in a salt and water bath (salt I oz., water 20 oz.) prior to toning. Fix and wash as usual.
Mercury Intensification.—For the purpose of eliminating from a mercury-bleached negative the last traces of a compound formed by the mercuric salt combining with the gelatine, Haddon has strongly advocated the use of hydro chloric acid. The bleached negative must be washed for ten minutes, and then immersed for three or four minutes in a bath consisting of dram of hydrochloric acid and To oz. of water. Next it is rinsed in water and transferred to a second acid bath, rinsed again, and placed in a third, then washed in several changes of water, and finally blackened as described under the heading "Intensification."