I purchased this book by The Edwal Laboratories, Inc, 3rd Edition, 1947 at a camera store junk box still wrapped. What I find interesting are the tips that are given; and these tips have been around for 51 years or perhaps longer since the 1st Edition was published August 1939.
1. To test the "clearing time" of fixer, Edwal recommends that you soak a piece of negative film 3 to 4 minutes first before placing it into the fixer.
2. Use Edwal Kwik-Wet in the developer to prevent airbell holes.