المنشط أو القلوى .. كتاب التحميض والطبع والتكبير

Third - Activator or Alkali ACCELERATOR or ALKALI:

The acidity of the show solution increases as a result of the addition of some preservatives (such as sodium bisulfite or potassium metabisulfite), and as the activity of the reducing agent decreases in an acidic medium, therefore work must be done to add an alkaline substance to
solution to perform the following functions:
(a) Acidic neutrality of preservative compounds, some of which are acidic in nature.
(b) Neutralization first-hand with hydrobromic acid resulting from the reduction of silver bromide (precipitated in the sensitive gelatin layer).
h) Keeping the revealing agent in an alkaline medium to increase its activity.

The following are examples of activated alkaline salts used in show solutions:
1- Sodium carbonate.
2- Potassium carbonate
3- Caustic soda
4- Caustic potash
5- Borax
6- Kodak (an alkaline compound produced by Kodak Company) stops Aden saw the day when they come to Orkan, and the extent of the activity of the display solution depends on the quantity and degree of chemical activity, the only global measure of the alkaline compounds that the solution carries. For example, Kodak 76-D bleaching solution contains Borax, which is less active in bleaching than Kodak.
The solution carried by Kodak DK60 a, and the activity of this last solution is less than another solution carrying sodium carbonate (as in Kodak developer No. 11-D). The chemical activity of the compounds that are included in the composition of the highlighting solutions depends on the degree of their alkalinity, which varies greatly according to the different salts. In order to express the degree of alkalinity, it was agreed to estimate it with numerical values ​​known as “pH-values.” Practically speaking, the photographer may not care to know the basis for estimating the pH value as much as it means to know “the degree of alkalinity or acidity of materials.” Therefore, we suffice here. By saying that the substance is considered neutral (like water) if the value of pH = 7, and if this value decreases, this indicates its tendency to acidity, and if this value exceeds that, this indicates its tendency to alkalinity.
And since it is very important for us from a practical point of view to know the degree of alkalinity of solutions of preservatives and stimulants that are predominantly circulated in the composition of display solutions, and we are also interested in knowing the degree of alkalinity of the mixture of solutions of these materials, so we show at the end of this page a table to show that:
Although the difference between the numerical values ​​indicating the degree of alkalinity of the solutions may appear to be slight differences at first glance, in reality they indicate very large differences, because the numbers indicating the pH value were built on a logarithmic basis. We explain this by saying that the solution that you form The degree of alkalinity = 10 pH The alkalinity scale is ten times higher than that of the degree of alkalinity = 9 pH. The degree of alkalinity of the latter is also ten times higher than that of another solution whose degree of alkalinity = 8 pH, and so on.