From the Chemicals Cupboard (Page Three)

dissolve in water and may need water as hot as 80°C to dissolve. The CRC supplies
Dimezone ‘S’. a Kodak version, which may be used as a direct equivalent, it dissolves
without problems and has better keeping properties.
Code 23. Metol. This will oxidise quickly in solution so add any suiphite as soon as the
metol has dissolved. You can add a small pinch (I or 2 g) of the suiphite before the metol to
reduce this, but don’t add too much or the metol won’t dissolve.
Code 36,48 and 78. Thiocyanates. These will absorb moisture from the air very readily, so
are best kept as a solution, e.g. 20%. If they are supplied as a solid the package will contain
a photographically inert gas, such as ‘Tetenal Protectan’. Some of these are inflammable so
take care when opening the package.
Code 48. Sodium Thiocyanate. Some formulae specify sodium thiocyanate liquid. This is
normally a 51% w/w solution (Kodak). lOOmI of this contains 66.8g sodium thiocyanate.
Code 54. EDTA FeNH Solution 50%. lOOmI of solution contains 65.5g ferric ammonium
EDTA. 132m1 EDTA FeNH, 50% is equivalent to lOOg EDTA FeNa.
Code 77. Sodium Sulphide, 60%. This grade is a hydrate and contains 40% water by weight. ~
It is a solid so lOOg of sodium suiphide 60% contains 60g sodium suiphide.
Code 81. Potassium Sulphite solution, 45%. lOOmi of solution contains 65.2g potassium
sulphite.
     
Chemical Substitutions.
Some chemicals are available in ‘anhydrous’ or ‘desiccated’, ‘crystal’, ‘monohydrate’ or
similar forms. For photographic purposes these can be interchanged provided that the
amounts used are adjusted. In effectt, these different forms contain different amounts of
water. Anhydrous contains no water, monohydrate contains one molecule of water for each
molecule of wanted chemical and so on.
Crystalline (crystal) forms of different chemicals may contain different amounts
depending upon the compound. Conversion factors are often given in photographic books or
as part of the formula itself. Remember that the greater the amount of water included in the
chemical, the greater the amount you will need to use to get the same amount of the required
compound.
     
Substitutions for some common are:
The formula calls for:                       You have: Multiply the formula amount by:
Sodium Sulphite crystalline                  Anhydrous                      0.5
Sodium Carbonate monohydrate                 Anhydrous                      0.8
Sodium Carbonate crystalline                 Anhydrous                      0.4
Sodium Bisuiphite                            Sodium Metabisuiphite          1.O
Sodium Acetate                               anhydrous Trihydrate (3H20)    1~7
Sodium Acetate trihydrate (3H20)             Anhydrous                      0.6
Sodium Thiosulphate anhydrous                Crystalline (Hypo 5G20)        l’6
Disodium Phosphate (121120)                  Anhydrous                      0.4
Disodium Phosphate anhydrous                 Dodecahydrate                  2.5
     
In many cases it is also possible to interchange sodium and potassium compounds (and some
others, such as lithium, too) but this needs to be done with care and may have effects that are
specific to the formula involved. Unless specifically allowed by your formula, treat such
substitutions as a basis for experiment.