1.  Field of the Invention
This invention relates to a method and apparatus for controlling the halogen ion concentration in a photographic processing solution. 
2.  Description of the Prior Art
Various photographic processing solutions are used for developing exposed silver halide photographic film.  These solutions have optimum compositions or formulations according to the kind of photographic film or material to be processed, such as color film, general black and white film, printing film, etc.  Furthermore, each developer performs best when the concentration of each chemical component is kept in a specific range.  However, as the development progresses some of the chemical components are partially consumed and others are increased by the intermingling of chemical components entering from the developed photographic film, whereby the composition of the developer is gradually changed and its developing ability or effectiveness is reduced.  For example, the developing agent is gradually reduced by oxidation during the developing of silver halide, but the halogen ions are dissolved in the developer by the reduction of silver halide to increase gradually the concentration thereof. 
To regenerate the photographic developer for repeated use, a method is generally employed in which a supplementary composition is added to the fatigued developer after a certain amount of film has been processed.  However, adding the supplementary composition may supply lost components, but cannot reduce the components increased by the development.  Therefore, the undesirable components increase with development use or time and gradually accumulate in spite of repeated regeneration, until the point is reached at which the developer cannot be regenerated by the addition of such supplementary compositions.  The photographic processing solution is then discarded and replaced with a fresh solution. 
In general, in adding the supplementary composition the volume of the processing solution is maintained at a constant value by removing or discarding the same amount of the solution as the amount of supplementary composition supplied, by overflowing or the like, and this somewhat reduces the increased undesirable components.  However, in order to reduce the components to desired concentrations, a large amount of the processing solution must be discarded. 
In, for example, a film containing mainly silver chlorobromide, emulsion, chlorine and bromine ions increase with usage in the developer.  In a film containing mainly silver iodobromide emulsion, the iodine ions released in the developer are exchanged with the bromine ions of silver bromide to increase the bromine ions.  Among halogen ions, bromine ions have a great influence on the processing ability of a developer, and an increase of the bromine ion concentration in a developer greatly decreases the developing speed.  Other ions, such as those of chlorine, increase in concentration development, but such increase does not have the bad influence on processing ability as do bromine ions and hence cause no trouble. 
A developer also contains various ions at high concentrations, and hence it is undesirable from a pollution prevention standpoint to discard the developer without first processing it to a non-toxic state to satisfy legally regulated waste water standards.  For such treatment large scale apparatusses and high costs are required. 
Thus, some means for regenerating the developing ability of a fatigued developer without discarding it, thereby enabling the repeated use of the developer, has been highly sought after. 
In general, silver ions in a fix solution, the concentration of which is desirably as low as possible, and Fe(II) ions in a bleach solution, which are desirably completely reoxidized to Fe(III) ions, can be comparatively easily regenerated.  Also, a fatigued developing agent can be easily regenerated by supplying the decreased component by its reduced amount. 
Halogen ions, particularly bromine ions, have a large influence on the properties of photographic materials even if the amounts thereof vary only slightly.  As mentioned above, halogen ions may be removed by known electrodialysis or electrolysis techniques using an anion-exchange membrane.  However, with these known methods the developer must be recontrolled to a definite concentration before use after removing the halogen ions. 
In addition, in photographic processing solutions other than the developer, for example a mono-bath type blix solution used for processing color photographic materials, halogen ions such as bromine ions also increase in concentration with use.  In these other photographic processing solutions the influence of the bromine ion concentration increase on the processing ability may be low compared with that of the developer, but if the bromine ion concentration increases too much it reduces the fixing speed.  Therefore, in regenerating these other photographic processing solutions it is preferable to remove the bromine ions in addition to supplying some supplemental solution.