Carroll, B. H., Hubbard, D. and Kretschman, C. M. 1968. The photographic emulsion. London: Focal Press.

This is a very useful publication because it examines the variations of the parameters in emulsion making. It's actually a reprint of a series of Papers written in the 1920's/30's and although the formulae & techniques may be old fashioned the methodology is still valid.
Ian