PHOTOGRAPHIC PROCESSES. 83 



saving both of time and solution is effected if several 

 plates, which have each received a similar exposure, 

 are developed at the same time. 



A dish of earthenware to hold a saturated solution 

 of alum, another for a similar solution of mercuric 

 chloride, and one for hyposulphite of soda or fixing 

 solution : — these should all differ in appearance, to 

 avoid the possibility of putting a solution into one, 

 which had previously contained another. 



The dishes being placed in a convenient position 

 in the dark room, one or two plates according to 

 circumstances are placed in the dark slide; every 

 precaution being taken during this and all subse- 

 quent operations for the exclusion of actinic light. 

 The exposure being made, the slide with its contained 

 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 Micro-photography. 

 No. I. Liquor Ammonia, ('880) 3 ii. 

 Bromide of Ammonia, 3 H. 

 Distilled Water, | 20. 



g2 



