edited by GEORGE L. GILBERT Denison University Granville. Ohio 43023
Macro Chromatography
SUBUlTTEOBY A. Hablch and H. R. Hiusermann Kanton=hUIe RImlbiihl Chemlsches Ina(ltut. RIml.tra..e 54. CH-8001 Zlrkh, Switzerland CHECKED BY
Paul F. Krause Unlverslty of Csnlral Arkamas Conway, AR 72032
Some principles of chromatography can easily be illustrated on a macroscopic scale by a simple demonstration model. I t consists of a transparent tubing of appropriate size for the column, some table tennis (e.g., Ping-Pong) balls as the stationary phase, and a mixture of beads of two sizes a8 the sample to be separated. Variation in retention times in "real"chromatography caused by different solubilities of comDonents in the mobile nhase or adsorption onto or inclusion'into the stationary phase, is achieved in our model by the different distances that the two kinds of beads have to travel on their way down the column. For our column we use plastic tubing of 150-cmlengthand 5.0-cm inner diameter packed with about 45 table tennis balls, 3.7 cm in diameter. T o hold the halls in the column, we diametricallv inserted a screw at its lower end. hut a niece of adhesive tape will suffice. Our sample consis& of a mixture of 10 yellow and 10 blue plastic beads of diameters 0.8 cm and 1.0 em, respectively. The beads must he spherical, not facetted. and should be without holes. to ensure a smooth run. Loading the column with the sample, the smaller heads roll down faster than the larger ones, which need more time to find a wav around the table tennis halls. Sometimes a bead is blocked, indicating permanent adsorption, and there is alwavs some band broadening. But finally, a complete separation is achieved. Classroom experience has shown that macro chromatography as demonstrated by this model is readily understood and is enjoyed by students. ~~~~~
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An Unusual Demonstration of the Behavior of Gases svsumo BY Arlel E. Fender John Abbon College St. Anne de Bellvua. (lus., Canada Davld N. Harpp MCGIIIunirerrny Montreal. aue.. H3A 2K8, Canada Joseph A. Schwarz Vanler College Montreal, Ow., H3X 2N9, Canada CHECKED BY
Luther K. Brlce Vlrglnla Polylschnlc InstlMe Blacksburg,VA 24061 Balloons lend themselves effectively to scientific demonstrations. Certain aspects of the gas laws as well as of shock waves can be dramatically illustrated by blowing up one balloon inside of another and then bursting the inner halloon. In order t o achieve this, one balloon (it can be some-
what smaller than the first) is stuffed inside a second balloon in such a fashion that the two necks end up in a concentric position. The inner balloon is then inflated, and its neck tied. The outer balloon is then blown up until i t is about twice the size of the inner one, and its neck is also tied. The resents some diffiinflation of of ~ the ~ inner ~ balloon ~ ~ course ~ culty since the rubber of both balloons has to he stretched. This in turn means that the Dressure inside the inner balloon is considerably greater than in the outer balloon. A special, lubricated, smooth and sharp needle (available through magic dealers as "Super Needle Through Balloon" can then be passed through the outer balloon without bursting it. (In addition this presents an opportunity to discuss the unique properties of ruhher.) A quick thrust of the needle then bursts the inner balloon; this is followed instantly by the explosion of the outer balloon. Presumably the latter effect is caused by the sudden increased pressure inside the outer balloon caused by the release of air from the inner balloon coupled with the shock wave generated. The transmission of energy in this fashion which we recognize as an "explosion" is thus dramatically demonstrated. ~
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mis needle is usually available from mailorder magic store dealerssuchas: LouisTannen Inc.. 1540Broadway.New Ywk. NY 10036; AI's Magic Shop. 1012 Vermnt Ave.. NW. Washington, DC, Perfect Magic. 4781 VanHorn. Suite 206, Montreal, Oue. H3W 1J1, Canada.
An Improved Demonstration ol Collold Flocculation Sus~m~ BYo
0. L. Crees Sugar Research InstHuIe Ma~Kay,Quee11.land,Auslralla E. Senogles James Cook Unlvenly o( N a t h aussnaland Oueensland, Australla CHECKED BY
Rlchard F. Jones Slnclair Communlly College Dayton. OH 45402 The use of small concentrations of synthetic polyelectrolytes to induce the flocculation of hydrophobic colloids is of widespread industrial importance. For example, these materials are used in the mining industry, in the recovery of metals and metal ores from slimes and suspensions, in the treatment of petroleum refinery and electro-plating wastes, in sewage disposal, in the pulp and paper industry, and in the treatment of cane iuice in suear mills. The nrocess is distinguished from the coagulation or precipitation effert resultinr from the addition of low-molecular-weight electrolytes to colloidal systems. We have found the following demonstration of flocculation hiahlv successful and more impressive than that previous1y;eported.l A sample of Premium Grade "Wyoming type" sodium bentonite2 (5-7 g) is dispersed in distilled water (1 L). This is best done by adding the bentonite to approximately Volume 63 Number 8 August 1986
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