Experiment 4

The Rate of Photographic Development

Procedure and Results

Procedure

a) Preparation of a developer: Dissolve 4.00 g of sodium sulfite (Na₂SO₃), 0.50 g of sodium bromide (NaBr), 1.20 g of metol and 4.00 g of sodium carbonate (Na₂CO₃•H₂O) (in this order!) in about 100 mL of distilled water in a labeled 400 mL beaker. Stir until each solid is dissolved before adding the next one. Dilute to 200 mL with more distilled water and stir well.

b) Preparation of stop bath: Pour 25 mL of vinegar (acetic acid) into a 400 mL beaker and dilute to 100 mL with water. Label the beaker.

c) Preparation of fixer: Weigh 24.0 grams of sodium thiosulfate (Na₂S₂O₃), 1.0 g of sodium sulfite (Na₂SO₃), and 2.5 g of sodium bisulfite (NaHSO₃) into a 400 mL labeled beaker. Add 100 mL of water. Stir until dissolved and thoroughly mixed.

d) Preparation of wash: Fill a labeled beaker with tap water.

e) Determination of optimum conditions and measurement of rate: Pour about 100 mL of developer into a 400 mL beaker and clamp in a copper water bath filled with tap water. Use a magnetic stirrer to keep the developer stirred. Measure the temperature of the developer until it is constant. (See the Figure below). At this time pour another 100 mL of developer into a beaker and set in ice.

The following steps must be performed by the light of the red safety lights only. The overhead lights must now be turned off.

Obtain some photographic paper from your instructor. Expose a piece of the paper (glossy side up) as shown in the Figure below for 10 seconds. Measure the time it takes for a good print to form when the paper is agitated (using tongs) in the developer. When finished, place in stop bath for 10 seconds, then into the fixer for 5 minutes, and finally, the wash for 5 minutes. If the print is very dark with low contrast, repeat with shorter exposure time. If it is very light with low contrast, increase the exposure time.

Adjust conditions until an acceptable print is obtained. Repeat this process, making a second print in the developer with this temperature. Be certain to record the times for the development and the temperature. Put the prints on a paper towel to dry so they may be included in your Results.

f) Measurement of rates at other temperatures: Replace the water in your constant temperature bath with a mixture of ice and water. Replace the developer with the chilled developer. Stir until the temperature is constant. Expose another piece of paper for the same time as in the previous step and develop to the same darkness (density). Record the time required for this development. Repeat to obtain a second trial at this temperature. Repeat this process for two more temperatures at least one of which is above 30ºC.

Results

Enter your results (temperature and development times) for each print into a table. Calculate the values of the development rate for each print at each temperature and enter these also in your table. These rates are calculated by dividing the number one by the number of seconds it took for the development process to take place (1/time (secs)). For example, if it took 10 seconds to get a print with the correct darkness, the rate would be: 1/10 secs = 0.10 secs^-1. Calculate and record the average of these rate values for each temperature. Make a plot of this data. Your prints should also be included in the Results section.

comments to: j byrd jim@chem.csustan.edu or m perona mike@chem.csustan.edu

02.03.99