FERROUS OXALATE DEVELOPMENT. 22$ 



solutions keep well, therefore any quantity of these can be 

 kept ready for mixing. The sulphuric acid is not essential 

 in the formula referred to ; it can be omitted. 



The bromide of ammonium solution may be added to the 

 developer as a restrainer, to counteract over-exposure in the 

 same manner and under the same conditions as in develop- 

 ment with pyrogallic acid and ammonia. 



This ferrous oxalate developer should be used in a flat 

 bath, precisely in the manner described for alkaline pyro- 

 gallic acid development During the operation the solution 

 must be made to wave to and fro over the plate, and the de- 

 velopment continued until the required density is obtained. 

 This will occupy about three minutes, as a rule. The addition 

 of bromide affects most powerfully the rate of development 

 and its character, making it slower and increasing the con- 

 trast of light and shade. For copying engravings, &c., where 

 only black and white is to be printed, the proportion of 

 bromide of ammonium may be advantageously increased. 



If during development or fixing any loosening or blister- 

 ing of the film should be observed, the plate must be 

 immediately rinsed in water and put into a solution of alum 

 (i oz. to I pint of water). After allowing to remain five 

 minutes in the alum solution, it should then be finished as 

 usual after this treatment ; and as all plates of the same 

 packet will probably be alike, it will be advisable with each 

 of these to use the alum bath after development, without 

 waiting for the appearance of blisters or loosening of the 

 film. 



The image generally makes its appearance in about a 

 minute, the deposit gradually increasing in intensity until 

 the development is finished. It is then to be well washed 

 and fixed in the following solution : 



Hyposulphate of soda . . 4 oz. 



Water . . . . ' . . 20 oz. 



