خطوات إعداد المحاليل .. كتاب التحميض والطبع والتكبير

Solution preparation steps

1- Weigh the salts with an accurate scale.

2- It is better to boil water and then cool it until its temperature reaches 45 degrees Celsius, and the wisdom of boiling it is to expel the oxygen carried by the air, which helps to confirm the salts involved in the composition of the show solution or others.

3- Water is poured into a graduated glass container or stainless steel container. It is always better when dissolving salts that the amount of water is less than the amount specified in the table. Composition of solutions, for example, or the final attempt should be 1000 cm, so it is better to dissolve the salts in 750 cm, then complete the final solution with cold water until the volume of the solution finally (including the salts) reaches 1000 names.

4- The salts are poured in gradually, with continuous stirring, until the salt is completely dissolved, and the next salt does not dissolve until after verifying that the first salt has completely dissolved. And track the same. The method with the following salts and so on. The salts must be dissolved according to the order requested in the table of the composition of the solutions.

5- After the end of the dissolution, the filtration process begins, in order to get rid of any sediment. Solid, possibly attached to salts.
We show in Figure 28 a summary of the previous steps. The process of filtration of solutions requires only a funnel and a piece of medical cotton - or circular filter paper that is folded in half first, then folded again and opened in a conical shape - and placed in the funnel. As shown in Figure 29-1. When pouring solutions into the filtering funnel, it is better to place any small object between the funnel and the mouth of the bottle in order to facilitate the expulsion of air from the inside of the bottle to be replaced by liquids (Figure 29), otherwise the funnel will be filled without the liquids descending from it.

Some prefer to follow another way to get rid of the filtration of some solutions. This is done by dissolving the salts (such as hypo- and potassium metabisulfite) as follows:

Place the required quantity if you put it in a piece of cloth on the mouth of a large bottle or a wide glass container. The ends of the cloth are thrown outside the mouth, then the container is covered with its usual lid, or a weight - such as a plate for example - is placed on top of it, so that the salt surface level is lower than the water level (Fig. 29-h), and it is left like this until it is completely dissolved. It is easy to dissolve the salt in this way, due to the saturated solution settling at the bottom of the bottle. Thus, the process of dissolving and filtration takes place easily without much effort.

6- A white card is placed on the bottle on which is written the type of solution and the required exposure time at a temperature of 18°C. It is okay to write the date of preparation of the solution as well, or any other necessary data such as the number of times it is used to display a certain number of films. In view of the possibility that the reducing agent may oxidize and deteriorate if exposed to air, the quantities of the solution that appear should be kept in bottles that are well closed with a rubber stopper, which is best, or with a cork or glass, noting that the glass stopper may stick to the mouth of the bottle and sometimes it becomes difficult to open it. If this happens, follow the method shown in Fig. 30 . When filling, the bottle must be filled with the solution to its mouth. No air should be left in it that may result in oxidation of the reducing agent. The normal temperatures are suitable for preserving the display solutions, and if the packaging is well done, the display solution will remain valid for several months, but it is certain that it will deteriorate if it is left exposed to the air, or at least in an exposed basin whose strength weakens.