Tested O v e r h e a d Proiection Series Compiled by HUBERT N. ALYEA Princeton University
the stage, interpose the black/clear shield, and turn on projector lamp. Remove shield in a few minutes. (b) Repeat using cell C-3, and interposing blue/yellow/red shield.
7. ENERGY (Continued)
D. Light Energy 2. CONSUMPTION O F LIGHT [Continued) c. Redox reactions Dem. 356Photochemical Oxidaiion of Thionin
Experiment developed by Clayton B. Lamb and his pupil, Gary Averett, at the U. S. Science Pavillion, Seattle, Washington, in 1962. To show: The photochemical bleaching of thionin (Lawth's violet C12H8N3S). Materials: Thionin, 6 N H2S0,, INohr's salt ferrous ammonium sulfate, 250 ml beaker; star-shield SD-349. Preparation of thionin solution. To 30 ml 0.001 M 10 thionine (0.23 g/liter) add 2 g FeS01.6 HxO ml 6 N H2S04;then dilute to 250 ml. Filter if necessary. Keeps a month in stoppered bottle.
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Procedure: (a) Fill C-1 with the thionin solution. Place on stage, and interpose the starshield. Turn on projector lamp. Fifteen seconds later pull the star-shield away. (b) Allow to stand in darkness a minute. (c) Repeat the cycle. Obseruations: Light induces the oxidation of the thionin by Fe++. The reaction is reversible in the dark. The blue image of the star is impressive. The cycle can be repeated many times. Alternate procedure: Surprising results are obtained using a 6 X 6-inch cardboard light-shield. Interpose the shield so that only a 1-inch vertical strip of solution is exposed to the projector light. At 5-second intervals pull the shield along, horizontally, to increase the width of the exposed strip, stepwise. Result: a series of strips of decreasing blueness form. HEIDT, L. J., J . Chem. Educ., 26, 525
Reference: (1949).
Dem. 357-Phoiochemical Reduciion of Fe(lll) by O x a k Acid
Experiment developed by LeRoy G. Hornbeck. To show:
The photo-reduction of Fe(II1). light
Fefa + HH~CIO, 4 Fe+%xdate Fe+>+ Fe(CN)a-a P ~ s s i a nblue
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Materials: C-2; C-3; FeClaaq, K3Fe(CN)6-aq, oxalic acid-aq, stirrer, black/clear or blue/yellow/red light shield, SD-349. Procedure: (a) Three quarters fill the cells of C-2 with water, and to each add several drops in this order: FeCS-aq K3Fe(CN)6-aq oxalic acid-aq. Set on
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C Circle
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No. 169 on Readers' Servics Card
Observations: (a) In a few minutes the cell exposed to light turns blue; Fe(II1) has been reduced photochemically to Fe(I1) which reacts with the ferricyanide to give Pmssian Blue. (b) With colored filters, blue is the most active, red the least, via blue >> yellow > red. Reference:
STONE,C. H., J . Chem. Educ., 6,630 (1927). Dem. 358-Bluepriniing
Experiment developed by LeRoy G. Hornbeck. To show: The photochemical reaction occurring in the making of blueprints. See previous demonstration for equations. Materials: Gelatin, FeCkaq., K,Fe(CN),aq, acid-aq., C-1 ; star-shield SD-349.
oxalic
Procedure: To 100 ml boiling water add 4 g gelatin; boil and stir until dissolved. Cool to near room temperature; pour into two beakers. To one add 1 ml K3Fe(CN)#-aq.To the other add 1m l oxalic acid-aq 1 ml FeCI3-aq. Now pour the two solutions into C-1. Set in complete darkness until gelled. Now place on projector, interpose star-shield, turn on projector lamp. Five minutes later remove the shield.
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Observations: In about 5 minutes the exposed gelatin turns blue; that behind the black star remains yellowgreen; upon removing the shield the image of the star is "startling." Reference: (1927).
STONE,C. H., J. Chem. Educ., 4, 630
Dem. 35+Diasa-printing
Experiment developed by LeRoy G. Hornbeck. To show: The effect of light on, and development of, diazo materials used in photo-copy work. Materials: Cell C-1. Technifax diazochrome film cut to fit C-1, holder made by taping two 5 X 5 X1/la inch clear Plexiglas plates together, along one side; 5 N NH,-aq., transparent line drawing or picture.
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Procedure: (a) Place in holder and expose line drawing and diazo-film to the projector light in that sequence for several minutes (find by trial). Momentarily project the diazo-film alone. (b) Then place it in 5 N NHhaq in C-1 on the stage. Observatims: (a) The transparency will project, but when it is removed, nothing is visible on the diazo-film (b) A moment after the diazo-film is placed in the NHa-aq. an image appears. Volume 44, Number 2, February 1967
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