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Kodak tropical acid hardening fixing bath for films and plates.

Sodium thiosulphate anhydrous150
Sodium sulfite anhydrous
Acetic acid glacial
Boric acid crystals7.5grams
Potassium double sulfate of aluminium15grams
Water to make1liter
Powdered boric acid dissolves only with great difficulty and its use should be avoided

Films and plates will be fixed properly in 10 minutes (cleared in 5 minutes) if a freshly prepared fixing bath has been used. Prolonged immersion at high temperatures is harmful.

The bath need not be discarded until the fixing time (twice the time to clear) becomes excessive, that is, over 20 minutes. The solution remains clear and hardens well throughout its useful life.

About 20–25 8×10 films or plates (or their equivalent in other sizes) may be fixed per 1 liter.

The fixer has the advantage over the other types of fixing baths which do not contain boric acid, that is gives much better hardening and has a lesser tendency to precipitate a sludge of aluminium sulphite throughout its useful life. The ingrediends other than sodium thiosulphate may be compounded as a stock hardener solution to be added to a solution of hypo, using Kodak F5a.