Tested Overhead Projection Series Compiled by HUBERT N. ALYEA
Princeton University Note: Glass plate may be used in place of cellophane. Add soap or other wetting agent to XI sol~ttianto aid in writing on glass or cellophane.
20. GROUP VII. THE HALOGENS
E. Iodine
Dem. 628-Secret
Dem. 625-Iodide
Writing (KI
+ Starch-aq + CIt-aq)
T o show: Secret writing with KI-aq developed by Clz-aq starch-aq.
+
in Iodized Salt
Experiment developed by Raymond P . Garman T o show: The presence of iodine ion in iodized salt. Materials: l\/lortonJs iodized salt, CL-aq, starch-aq, CS?, H-3. Procedure: (a) Dissolve 3 g iodized salt in 10 ml water; project in culture tube in H-3. Add 1 drop C1,-aq, shake vigorously (if the solution is not slightly brown now, add a second drop of Clz and shake; however do not add too much CL). Pour half of the solution into a second culture tube. Project both tubes in H-3. (b)To one add 5 ml CS2(CARE: fire hazard) and shake. (c) To the other add 5 ml starch-aq and shake. Observations: (a) The small amount of I- in the salt is liberat,ed as I2by the Clz-aq; this colors the solution faintsly brown. (b) The CS2 concentrates the I, to form a pink (dilute) to purple (conc.) solution. (c) The starch-aq forms hlue starch-iodine.
Materials: A 4 X 4-in. sheet of cellophane cottontipped swah, 5 ml IiI-aq 2 g starch, C-1, CI,-aq.
+
+
Procedure: Using the swab as a pen and 111 starch as ink, write a "secret message" on the cellophane. Dry slightly. Project C-1 full of water to which dropperfuls of CLaq have been added. Dip the sheet into the solution. Observations: The chlorine liberates iodine, which colors the starch hlue: the writing appears darkly on the screen. Dem. 629-Secret
Writing (Starch
+ Iodine)
T o show: Secret writing with starch developed by iodine. Materials: A 4 X 4-in. cellophane sheet; starch-aq, tincture of iodine, cotton-tipped swab.
T o show: That potatoes contain starch
Procedure: Using the swab as a pen, and the starch-aq as ink, write a "secret message" on the cellophane. Let dry somewhat. Project C-1 2/3 full of water. Put the cellophane in C-1, then add two drops of tincture of iodine.
Materials: Potato, knife, mortar and pestle, tincture of iodine, C-2 filter paper, funnel.
Observations: The "secret writing" appears blue as the iodide-starch complex is formed.
Procedure: Grind a slice of potato with 20 ml of water, and filter to give a clear extract. Project C-2 with one cell threequarters full of water and cell 8 '/4 full of the potato extract. Add one drop (only) of tincture of iodine to each.
Note:
Dem. 626-Starch
in Potatoes
Experiment developed by Raymond P. Garvin.
Observations: The solution in cell 1 is slightly yellow; in cell 2 the iodine forms a blue compound with the potato starch. Dem. 627-Secret
Writing (KI
+ Clrgas)
21. METALS OF GROUPS IV-VIII.
A. Group IV. (Ti, Sn, Pb) Dam. 630-TiCld'Hydrolyris
T o show: The hydrolysis of t,itanium tetrachloride. Materials: Wide-mouth 2-02. square bottle with 2hole stopper, inlet and outlet tubes 2 in. long with 1-ft rubber tubing each; TiCI,.
Experiment developed by Raymond P . Garman. T o show: 111-ink writing developed by C12-gas Materials: A .5 X 4-in. sheet of cellophane; . 111-aq, cotton-tipped swah, C12-gas,C-1, detergent. Procedure: Using t.he swah as a pen and KI-aq as ink, write a "secret message" on the cellophane sheet. Drop it into C-1 and project. Dry thoroughly until it is invisible. Drop it into C-1 and project. Now blow C12gas into the cell. Observations: The chlorine brings out the invisible writing as brown 12. Reaction CI2 21-+ 2C11% (brown).
+
Glass plate may be used in place of cellophane
+
Procedure: Project; blow gent,ly into rubber tubing leading into bottle containing 2 ml TiCL Observations: Smoke clouds of TiOp from hydrolysis of TiCl, with moisture in the air. Dem. 63 1-Spongy
Tin
Experiment developed by Kenneth V . Jaclcman. T o show: The formation of spongy tin. Materials:
SnC11.2H20,6 A t HCI, 20-mesh Zn, C-2.
Procedure: Project 1 g SnCIz.2H20
+ 20 ml H 2 0 +
Volume 46, Number 6, June 1969 / A451
