1)  Photographic Emulsion Technique,2nd Ed., 1948, by T. Thorne Baker.  (Available as an inexpensive unbound photocopy from usedbookcentral.com).  Highly recommended.

2) The Darkroom Cookbook,2nd Ed, by Stephen G. Anchell.  The chapters on handling chemicals are a must-read. 

3)  SPSE Handbook of Photographic Science and Engineering, Edited by Woodlief Thomas, Jr., 1973.

4)  The Dictionary of Photography, by E. J. Wall, 1912. Google Read

5)  Photography with Emulsions, by William De W. Abney, 1885. (a Elibron Classics reprint).  Google Read

6)  Photographic Emulsions: Their Preparation and Coating on Glass, Celluloid and Paper, Experimentally, and on a Large Scale, by E. J. Wall, 1929. (Available as a UMI Books on Demand bound reprint.)  Note: Even as a reprint this is expensive and it's more for the historical tone than easily useful info. That said, I believe the experience of swimming in the time stream is invaluable to mastering a historical process.  Kirk Keyes has posted a very readable copy on his website.

7)  Making and Coating Photographic Emulsions, by V. L. Zelikman and S. M. Levi, 1964.  (a UMI Books on Demand bound reprint.  Note: This book is serious chemistry.  It's mostly over my head, but I keep chewing away at it, a page at a time. I think it's probably excellent. 

8)  The Encyclopedia Britannica, 1911, Vol. XXI, PAYN to POLKA (i.e. Photography).

9)  The Focal Encyclopedia of Photography, McGraw-Hill Book Company, 1969.   

10)  Silver Gelatin, by Martin Reed and Sarah Jones, Amphoto Books, 1996.   This is really about using Liquid Light or the other prepared emulsions, but there is a bunch of solid information for the person who may not have an extensive darkroom background.  In addition, there are a number of emulsion recipes from original publications, primarily Baker and Wall.  This book is currently on the used book market and very expensive.  If you have a limited book budget, it is not the first place to put your money.  There may be a new edition in the works.

11)  Practical Color Photography, by E. J. Wall, 1928.  Google Read

12)  Photographic Science, by Earl N. Mitchell, 1984.

13)  History of Color Photography, by Joseph S. Friedman, 1947.

15)  Photographie mit Bromsiber-Gelatine, by Josef Eder, 1890. (in German).

16)  Successful Negative Making, 2nd Edition, by T.Thorne Baker, Focus Photographic Manuals No.1, 1905.  This booklet doesn't have any emulsion recipes, but rather speaks to the best ways to handle the commercial plates of the (1905) day, and is therefore a gold mine of practical information for working with our own plates.  My copy is very fragile and can't be opened fully for scanning, so I will be slowly transcribing it onto the Light Farm.

17)  Modern Dry Plates, by J. M. Eder, 1881  Google Read.

18)  Memoirs of a Photochemist, by Dr. Fritz Wentzel, published by the American Museum of Photography, 1960.  Although this doesn't contain much technical info, it is one of my favorite 'good reads', — a delight and nearly as good as time travel.

19)  Dye Transfer Materials, by James Browning. pdf File

20)  The Photographic Emulsion, by Carroll, Hubbard, and Kretschman, The Focal Press.  This book is in the process of being scanned into The Light Farm. To check out its progress, go here.

For those interested in the deep physics and chemistry of photographic materials, the classic read is The Theory of the Photographic Process,Third Edition, by C.E. Kenneth Mees and T.H. James, 1966.