Latent bleaching

Another approach to estimating the size of a latent image center uses redox buffers to determine the size at the transition potential between dissolution and growth. These buffers either develop the latent image centers, bleach them, or do neither. Konstantinov and associates (203,204) used the Gibbs-Thomson equation to analyze results obtained by this method. 

Figure 18. Two-stage development method to reveal latent image bleaching during development [86],...

Tani [90] has examined the properties of silver clusters by means of redox buffer solutions, and showed that the oxidation potential of latent images formed by sulfur-plus-gold sensitization was much more positive than for those formed in unsensitized, sulfur-sensitized, reduction-sensitized, and iridium-sensitized emulsions. The oxidation potential of fog centers with excessive sulfur sensitization was much more positive than that of fog centers with excessive reduction sensitization. In general this reflects the relative ease of bleaching of silver centers compared with silver sulfide centers. 

There is thus very little independent production of chlorine and the principal alkalis, NaOH and KOH. The inability of producers to vary the nearly constant ratio of chlorine to alkali is a constant problem to the industry. Market conditions from time to time make it important to separate some of the production. Plants dedicated to chlorine or sodium hydroxide then may appear. The processes involved in these plants also have great historical interest, and therefore most of this chapter is dedicated to them. Section 15.2 covers the production of chlorine, and Section 15.4 covers the production of caustic soda. Section 15.3 recognizes the separate importance of hypochlorites. These require the combination of chlorine with an alkali material and are not examples of the independent manufacture of the two. However, their major use is as latent sources of chlorine, and they are considered members of the active chlorine family [2], Their characteristic use in sanitation or bleaching depends on the fact that the chlorine in the hypochlorite group is in the -1-1 oxidation state and is a strong oxidizer. 

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