MAY, 1948
0
MISCELLANEOUS EXPERIMENTS E. K. BACON Union College, Schenectady,.New York
COMPARISON O F REACTION RATE IN THE SOLID STATE AND IN SOLUTION
thiosulfate, however, shows a slightly greater degree of instability, having poorer keeping qualities than tbe Powdered mercuric chloride and potassium iodide sodium acetate solution. With the indicated concenare placed in a large porcelain mortar and exhibited trations, a beautiful development of crystals results to show that there is no visible reaction. The mixture when the cell is projected on the screen and then is then ground vigorously with a pestle, calling attention seeded. to the physical effort required to produce red-colored CHEMICAL SUNSET mercuric iodide. The expefiment is then repeated in a A spotlight projected through a jar containing a second mortar, and the same red mercuric iodide results when, instead of grinding, water is added. A solution of sodium thiosulfate is reflected by a mirror variation is to dissolve the powders separately in water on a screen. When hydrochloric acid is added, the projected light slowly changes from yellow to deep and then mix the solutions. red and then extinguishes. This experiment is a VISUALIZING CRYSTAL FORMATION modification of that described in "Lecture DemonstraIt is possible to make visible on a screen the develop- tion in General Chemistry" by Paul Arthur, McGrawment of crystals in a glass cell, 2.5 mm. X 5 mm. X Hill Book Co., New York, 1937. 10 mm., substituted for the slide holder of a projection An 800-ml. beaker, or better, a square battery jar lantern. Concentrations of 66 grams of Na&Oa .5Hz0 about four inches on a side is filled with 700 ml. of in 15 ml. of water or 35 grams of NaG&Oz.3Hz0 in water and supported on a ring stand. A mirror is 20 rnl. of water give a degree of supersaturation that supported by a clamp on another ring stand in front of results in a not-too-rapid growth of crystals when the jar of water. A microscope illuminator furnishes seeded. The required amount of crystals and water a convenient spotlight and is arranged hack of the jar may he placed in the cell, which is immersed in a of water so that the light passes through the jar on to beaker of water, and then heated to boiling until the mirror and is then reflected on the screen back of solution is effected. The solutions should remain stable the demonstrator. if covered with a watch glass and cooled. Sodium Five grams of NaaSz0,.5Hp0 is added to the water
%2
and quickly dissolved by stirring. Five ml. of concentrated hydrochloric acid is then added and stirred into the solution. Within an elapsed time of 30 seconds to one minute, colloidal particles of sulfur begin to form. Observed a t a right angle to the jar, the scat-
JOURNAL OF CHEMICAL EDUCATION
tered blue light may be seen while the projected light on the screen turns to deep red and extinguishes. The experiment simulates in a striking demonstration the conditions under which the setting sun is observed through the dust layer close to the earth.
