PHOTOGRAPHIC PROCESSES. . 97 



The developer is now poured off and the plate 

 washed for a few minutes. If not sufficiently dense 

 (especially when owing to under exposure), the 

 washing is continued for some time, and the ordinary 

 pyrogallic acid and silver solution, mentioned under 

 the wet process, employed. 



Whether intensified or not at this stage, the nega- 

 tive is quickly washed under the tap and placed in a 

 solution, consisting of: 



Hyposulphite of Soda, 2 oz. 

 Water, 10 oz. 



(this solution should be fresh), where it is left for 

 about five minutes. 



After all creaminess has disappeared from the back 

 of the film, the plate is washed in frequent changes 

 of water, for not less than six hours. It is then 

 placed in a saturated solution of alum for fifteen 

 minutes, and again thoroughly washed. 



After this washing, if the negative on examination 

 appears to lack density and be deficient in vigour 

 owing to over-exposure, it is immersed in a saturated 

 solution of bichloride of mercury, until perfectly 

 white; again thoroughly washed for several hours, 

 and finally placed in a solution consisting of: 



Liquor Ammonise, 3 drachms. 

 Water, 10 oz. 



which changes the white colour to a dense black. 



By modifying the strength of this solution, any 

 density between that produced by the mercuric 



H 



