DEFECTS IN NEGATIVES. 147 



alkaline pyro development is superior to ferrous oxa- 

 late with dry plates. No intensification should be 

 attempted with wet plates, other than that obtained 

 by ordinary development. This is especially the case, 

 when the negative is required for enlargement. 



For direct printing, a thin negative obtained with 

 a wet plate, sometimes gives better gradations when 

 subsequently intensified with silver. A dry plate, 

 if the ferrous oxalate development is stopped before 

 the slightest fogging appears, generally requires in- 

 tensification with mercury and ammonium hydrate 

 after fixing, especially if intended for the production 

 of lantern transparencies by contact. 



From experiments with different sensitive com- 

 pounds it seems probable, that iodide of silver, as 

 its maximum intensity ends suddenly in the indigo 

 portion of the spectrum, will give the greatest 

 differentiation, and should therefore be used with 

 delicate structures. 



Bromo-iodide emulsions depend for the character 

 of their sensitiveness on the condition to which the 

 emulsion is brought as regards colour during the 

 cooking process, and as this sensitiveness extends 

 considerably into the invisible part of the spectrum, 

 a determination of when and with what structures 

 they should be used, becomes a very difficult matter. 



The amount of intensification required will be 

 found to vary directly as the magnifying power of the 

 objective. 



To sum up. The kind of plate to be employed, 

 depends on the character of the object, nature and 



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