Tested Overhead Projection Series Compiled by
HUBERT N . ALYEA Princeton University
15. BORON AND SILICON
B. Silicon 3.
16. CARBON AND ITS INORGANIC COMPOUNDS
A. Carbon
SILICONES (Continued)
1 . MODELS Dem. 475-Selecfive
Wetting
To show: Oil-soluble and water-soluble dyes being wetted by silicones and water respectively.
Dem. 477-Crydal
Structure: Diamond vs. Grophife
To show: Why on the basis of crystal structure graphite is greasy wherkas diamond is hard
Materials: Chlorsilanes, NHraq, three 4-02 widemouth bottles, two funnels, filter paper; water colored blue with vegetable dye; toluene colored red with oilsoluble red dye (e.g., Oil Red). Procedure: Macro: Hang filter paper for 10 min in unstoppered bottle containing 20 ml chlorsilane mixture; then remove and suspend in NH3-aq vapor a minute to neutralize any acid on the paper. Project cell C-2 carrying a funnel and untreated filter paper in cell 1, and funnel with treated paper in cell 2. In a bottle shake 20 ml toluene with 10 ml water, and inlmediately pour half of it through the funnel into cell 1, the other half through the funnel into cell 2. Obsevvations: Cell 1 colors blue; cell 2, red; the water runs through the untreated paper, the toluene through the silicon-coated paper.
Dem. 476Resistonce of Silicone Rubber to Heat and Cold
To show: The resistance of silicone rubber, versus natural rubber, to high and low temperature.
SD-477.
Materials: Strips of silicone rubber and of natural (vulcanized or unvulcanized) rubber about 5 X '/z in.; alcohol burner, acetone, dry ice, 400 ml beaker, 6 X 6 X 1 1 / in. ~ block of wood, hammer.
Special Device SD-477, see Figure. Grooves ill a 5 X 5 X 1 3 / ~ i n box . with transparent sides allows 5 X 47/8 X in. inserts to slide horizontally. Black dots painted on the inserts show in 3 dimensions the position of carbon atoms, in the diamond and graphite lattices, and how in the latter "layers" of hexagons of carbon slide past one another.
Procedure: (a) Heal. In the projector, stretch strips of silicone and of natural rubber to show elasticity. Now hold each horizontally over a lighted alcohol burner in the projector. (b) Cold. Project the two strips, showing their elasticity. Macro: Immerse them in acetone-dry ice mush for 2 full minutes. Project to show they are no longer elastic. Now hammer each on the block of wood. Let warm up to room temperature and again project to show elasticity. Obserualions: (a) Both are equally elastic. The natural rubber catches fire a t a low temperature and bums. The silicone rubber only chars, and a t a higher temperature. (b) Both rubbers lose their elasticity a t low temperature; the natural rubber shatters like glass. Both regain their elasticity upon re-warming to room temperature.
Crystal Models
2. ABSORPTION O N A CIGARETTE FILTER Dem. 478-Abwrption
of Tars
To show: The absorption of tobacco tars by a cigarette filter. Materials: A filter cigarette, 2 U-tubes fitting G". cotton, isopropyl alcohol. Procedure: Cut a cigarette into two parts so the total length of tobacco is the same in both. Insert the cigarettes projecting from one limb of each U-tube. Push a small wad of cotton into the bottom of each Volume 45, Number 3, March 1968
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