The DARKROOM COOKBOOK, Third Edition

330 THE DARKROOM COOKBOOK
The formula specifi es: You have: Multiply by:
Sodium metabisulfi te Potassium metabisulfi te 0.855
Sodium ascorbate Ascorbic acid 0.889
Sodium ascorbate Sodium isoascorbate 1.0
Sodium isoascorbate Ascorbic acid 0.889
Sodium isoascorbate Sodium ascorbate 1.0
Sodium thiosulfate, anhyd. Sodium thiosulfate, cryst. 1.57
Sodium thiosulfate, cryst. Sodium thiosulfate, anhyd. 0.64
Sodium bromide Potassium bromide 1.16
Potassium bromide Sodium bromide 0.86
Sodium sulfate, cryst. Sodium sulfate, anhy. 0.44
Sodium sulfate, anhyd. Sodium sulfate, cryst. 2.27
Sodium Sulfi te Conversion
Crystalline sodium sulfi te is not as common as it once was. Photographic chemical suppliers
will usually provide the anhydrous salt unless otherwise specifi ed. If you happen to obtain
the crystal or decahydrate form you can use the following conversion factors:
The formula specifi es: You have: Multiply by:
Sodium sulfi te, anhyd. Sodium sulfi te, cryst. 2.0
Sodium sulfi te, cryst. Sodium sulfi te, anhyd. 0.5
Sodium Carbonate Conversion
Sodium carbonate is one of the most commonly used ingredients in photographic chemistry.
It is commercially available in three forms, differing by the amount of water molecules each
contains. The three forms are anhydrous (also known as desiccated), monohydrate, and crystal.
Crystal is rarely seen today in photographic practice.
Of the three, the monohydrate form is the most stable and the best to use for photographic
purposes. The crystalline form is the least stable. However, as is often the case, a formula
may call for anhydrous and you may have monohydrate, or a chemical supplier may sell
you the anhydrous variety, and so on. In any case, the following table makes for easy conversion
from one to the other.
Today, most formulas specify sodium carbonate, monohydrate. If a formula requires one
of the other two forms, anhydrous or crystal, or if only one of the others is available, use the
following table for conversion:
The formula specifi es: You have: Multiply by:
Sodium carbonate, mono. Sodium carbonate, anhyd. 0.855
Sodium carbonate, mono. Sodium carbonate, cryst. 2.31
Sodium carbonate, anhyd. Sodium carbonate, mono. 1.17
Sodium carbonate, anhyd. Sodium carbonate, cryst. 2.7
Sodium carbonate, cryst. Sodium carbonate, mono. 0.433
Sodium carbonate, cryst. Sodium carbonate, anhyd. 0.37