To start with, if I wrote a book today (I am as you know) it probably would not be UPDATED in the future due to the lack of R&D on analog. This is a sad note.

I spent the day at GEH with many of the people there discussing conservation issues and recreating historical processes. There is too much for one person to cover, so the history of KI added to emulsions will have to take a side line to the huge overall history of Analog, sorry to say.

Added to the halides you mention there are Fluorine and Astatine. Now, these are not used, but why not would iin itself cover a chapter in a book as would the reasons for not using Calcium, Magnesium and other salts of halides. This is not trivial, it is more than a lifes work of many individuals. And, few are interested. This is, in part, hard core chemistry, and the early 20s is soft core in terms of today's knowledge. So, as things move forward, Phlogiston theory is forgotten.