PHOTOGRAPHIC FORMULAE 271 



HARDENING BATH 



Formalin 1 oz. 



Water 10 ozs. 



Soak prints or plates for about 10 minutes and wash. 



INTENSIFIERS. 1. Mercury 



A. Mercuric chloride (corrosive sublimate) .' 1 oz. 



Hot water 16 ozs. 



This will give a saturated solution ; when cold pour off the 

 solution from the deposited crystals and add 30 drops hydro- 

 chloric acid. 



B. Ammonia (-880) 20 drops 



Water 1 oz. 



Well wash plates till free from hypo, soak in A until 

 bleached, wash again, and blacken in B. Wash for J hour in 

 running water. Solution A may be used repeatedly. 



2. Chromium (C. Welborne Piper). 



Potassium bichromate .... 10 grains or 23 grammes 

 Strong hydrochloric acid . . 5 minims 0-3 c.c. 



Water 1 oz. 1000 



Bleach in solution, wash until free from yellow stain, and 



re-develop in Amidol or other non-staining developer. 



Prolonged washing after fixation is not necessary with 



this intensifier, and the process may be repeated if greater 



intensification is required. 



REDUCERS 



1. Howard Farmer's. Attacks thin part of image first and 

 increases contrast. 



Hypo solution 1 in 5 



Add enough Potassium ferricyanide (red prussiate of potash) 

 solution to give a pale yellow colour. 



Negatives must be thoroughly soaked in water before 

 immersion in this solution. As soon as reduction has pro- 

 ceeded far enough, plunge into water and wash thoroughly. 



2. Persulphate. For use with negatives that are too 

 contrasty ; attacks dense portions first. 



Ammonium persulphate 30 grains or 35 grammes 



Water 2 ozs. 1000 c.c. 



Concentrated sulphuric acid . . 1 drop 18 drops 

 Use solution fresh. 



