above the upper tee. Acrystallizing dish of about 10cm dia is suspended by wire midway down the second glass tube. An inexpensive 1500-W hair dryer is clamped so that it blows into the crystallizing dish that serves to concentrate the hot air around the glass tube and also permit viewing. If the hair dryer is mounted too close, its safety switch will turn it off. For enhanced visibility, aquarium lamps in appropriate safe mountings may be clamped behind and above the '?lotnglass tube and behind and below the "cold* glass tube. In operation, ice and ice water are placed in the expanded polystyrene cup and the hair dryer is turned on. ARer a short time you can see the pink solution descending from the wld side and the blue solution ascending from the hot side. Close examination will show color streaming. The thermosiphon is visible in modest size classrooms and is a dynamic demonstration of the shifting equilibria involved. The more expensive version of the thermosiphon is made wmpletely of glass tubing and requires a skilled glass blower. Dimensions are given in Figure 2. Acknowledgment JLB was supported by the NIH Minority High School Research Apprenticeship Program. RB first saw a primitive version of the thermosiphon a t a science fair in New Zealand and thanks the originator for the idea. Figure 2. The all-glass thermosiphon. All dimensions are in millimeters Literature Cited 1. Zeltmann, A H.;Mahnyaff, N.A: M e ,L. 0. J Phys. C h m . 1968,72, 121. 2. Ophardt,C. E. J C h .Edue. 1980.67,463. 3. Shakhsahiri, B. 2. Che& &mnsfrations, Vol. 1, 280, Universitj af Wiecrmsin Press,Msdi~on,WI. 1983.
Bleaching with Chlorine: Another Tomato Juice Demonstration Thomas M. Nemeb and David W. Ball' Cleveland State University Cleveland. OH 44115
Chemicals 'calcium hypochlorite 12 M hydrochloric acid tomato juice
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~ e b o r a hWhalen and David Blackman Un vers fy of tne Distr ct of Col~mbia washington, DC 20008
Procedure
When saturated bromine water is added carefully to tomato juice, . . an array of colors is produced (I).This demonstration can be seen on the cover of this Journal's December 1986 issue. The visual appeal of this demonstration inspired us to explore brominkwater reactions with other carotenoid-containing substances;' regretfully, none supplied as vibrant a visual array. The lessons of the periodic table suggested to us that we trv a different halorren. We have found that. bv bubbline cfiorine gas througK a cylinder of tomato juice, dramat; bleaching of the pigments is produced. The similarities and differences between the bromine and chlorine reactions act as a catalvst for the discnssion of the relative reactivities of the hal"ogens, as well as an introduction to the bleaching effects of chlorine.
a
'Author to whom correspondence should be addressed 'Among the carotenoid sources tried were V-8 juice, carrots, peaches, sweet potatoes, egg yolks, red and green peppers, and beets. Only the V-8 juice gave a similar reaction with the bromine water. Curiously, the carrots showed linle change in color. Journal of Chemical Education
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Assemble the apparatus according to the figure.
Checked bv
154
Apparatus 100-mLgraduated cylinder 50-mL filter flask ring stand -3 ft of rubberlplastic hose disposable pipet hose clamps metal scaop rubber gloves apparatus clamps
CAUTION:Chlorine gas is toxic. This demonstration should be carried out in a hood. Rubher gloves should be worn when performing this experiment. Set up the apparatus as depicted. The graduated cylinder should be filled only about half way with tomato juice (to keep it from bubbling over). The mbber hose should be connected using hose clamps to ensure that the chlorine gas does not leak through the connections. To generate chlorine gas, add about 15-20 mL of concentrated hydrochloric acid to the fdter flask. When ready to perform the demonstration, add a large swopful of calcium hypochlorite to the filter flask and immediately close offthe flask securely with a rubber stopper. Chlorine gas is generated by the following aqueous reaction:
(Alternately, chlorine gas can be dispensed from a leeture bottle directly into the mhher hose.) As the chlorine
bleached not only from the sun, but also from the chlorine bleach in the pool water. CI.
Acknowledgment
This demonstration was prepared under the auspices of the Freshman Honors Chemistry Program, directed by John Luoma. Helpful suggestions by Tom Flechtner are appreciated. Literature Cited 1.MseBeath, M. E.; Richardaon,A. L.J
Ckm Edue. 19% 63.1W2
Demonstration of the Common Ion Effect Submined by
E. Koubek
U.S. Naval Academy Annapolis, MD 21401 Tomato Juice Checked by
Jack L. Lambert
Kansas State university Manhattan, KS 66506
Schematic of setup to bleach tomato juice with chlorine gas gas begins to bubble through the tomato juice, it dissolves in the liquid. Eventually (
