DEFECTS IN NEGATIVES. 135 



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 chaacter 

 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, 

 and beyond the scope of a work of this description. 

 We shall therefore content ourselves with the indi- 

 cations for their employment already given. 



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 intensity of the illumination, and magnifying 

 power of objective. The development depends on 

 the purpose for which the resulting negative is 

 intended, the character of the object, and the kind 

 of plate. 



It is often impossible to obtain a sufficiently dense 



