PHOTOGRAPHIC PROCESSES. 95 



plates may be put aside, till another batch has been 

 exposed, or for an indefinite period, and developed 

 at leisure. 



The following formulae are recommended by Mr. 

 Swan for the development of the dry plates prepared 

 by him. 



There are two different developers, alkaline pyro- 

 gallic acid and ferrous oxalate. The former is pre- 

 ferred by many, especially for views and portraits, 

 on account of the control it gives the photographer 

 over the character of the resulting negative. We 

 shall describe it first, although the latter has given 

 more satisfactory results in Photo -micrography. 



No. I. Liquor Ammonia, ('880) 2 drachms. 

 Bromide of Ammonia, H drachms. 

 Distilled Water, 20 ounces. 



This solution will keep for some time if the bottle 

 containing it is securely corked. Care should be 

 taken that the ammonia is the full strength specified, 

 if weaker the whole formula will be ruined. 



No. II. Pyrogallic Acid, 4 grs. 

 Water, 2 oz. 



This solution should be mixed immediately before 

 development. 



The plate or plates being removed from their re- 

 spective slides, are placed in the ebonite dish. 



An equal quantity of No. I. solution is added to 

 No. II., and the whole poured equally over the plates 

 which are left at rest in it. 



