garryl said:
Back in the beginnings of photography, salt was used as the fixer(1850's). It was Sir John Herschel that suggested that we switch to Sodium Hyposulfite
as being faster and better.
Herschel suggested that method, as I recall, because Fox Talbot was complaining that his calotype negatives and prints turned dark over time, no matter how long he soaked them in the salt water. Herschel "fixed" them in a matter of minutes with the hypo solution and, as they say, the rest is photographic history.
Salt water is *not* an effective fixer, even with very long soak times -- neither sodium chloride solution nor sea water. Sodium sulfite will (eventually) fix a negative, but it has extremely low capacity (likely to require 4-5 changes of solution for a roll of film) and takes literally days (2-3 days with the above changes of solution) to work. Most, if not all of the other substances that will complex and dissolve silver halide crystals (thiocyanates, for instance) will also attack the image silver, resulting in bleaching (thiosulfate bleaches a little in an acidic solution, but not enough to notice or even measure in a reasonable fixing time). There's a good reason we're still using thiosulfate fixers after more than 150 years.