274 PHOTOMICROGRAPHY 



Dilute 1 part with equal quantity of water and develop for 

 4J minutes at 60 F. 



Wash for J minute in running water. 



2. Reversal. Potassium permanganate. 2 grms. or 17 grns. 



Sulphuric acid 10 c.c. J oz. 



Water 1000 20 ozs. 



Or potassium bichromate may replace the potassium 

 permanganate in proportion of 5 to 2. 

 Reversal is complete in 3 or 4 minutes. 

 Wash 30 seconds or till stain of bichromate disappears. 



3. Redevelopment. Replace the plate in the first developer in 



bright light until completely blackened (3 or 4 minutes). 

 Wash 30 seconds. 



4. Fix. If desired, in hypo 15%. 



Wash J of an hour. 



5. Dry. Spontaneously in air. 



6. Varnish. Gum dammar 1 part ; benzole 10 parts. 



Equivalent Weights of Dry and Crystalline Chemicals. 

 Sodium sulphite, dry 



One part = two parts crystals Na 2 S0 3 7H 2 0. 

 Sodium carbonate, dry 



106 parts=286 parts crystals Na 2 C0 3 , 10H 2 0. 



(Soda crystals or washing soda.) 



The quantities given in the developing formulae refer to 

 the crystalline chemicals. The sodium sulphite crystals may 

 be replaced by half their weight of the dry salt, and the soda 

 crystals by one- third the given weight if dry carbonate is used. 



Relation of English and Metric Weights and Measures 



