edited by George L. Gilbert
te/ted demon/tration/ Submitted
Macro Chromatography by
A. Hablch and H. R. Hausermann Kantonsschule Ramibuhl Chemisches Institut, Ramistrasse 54, CH-8001 Zurich, Switzerland Checked by
Paul F. Krause
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University of Central Arkansas Conway, AR 72032
Some principles of chromatography can easily be illustrated on a macroscopic scale by a simple demonstration model. It 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 as the sample to be separated. Variation in retention times in “real”chromatography caused by different solubilities of components in the mobile phase 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-cm length and 5.0-cm inner diameter packed with about 45 table tennis balls, 3,7 cm in diameter. To hold the balls in the column, we diametrically inserted a screw at its lower end, but a piece of adhesive tape will suffice. Our sample consists of a mixture of 10 yellow and 10 blue plastic beads of diameters 0.8 cm and 1.0 cm, respectively. The beads must be spherical, not facetted, and should be without holes, to ensure a smooth
Denison University Granville, Ohio 43023
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 it is about twice the size of the inner one, and its neck is also tied. The inflation of the inner balloon of course presents some difficulty since the rubber of both balloons has to be stretched. This in turn means that the pressure inside the inner balloon is considerably greater than in the outer balloon. A special, lubricated, smooth and sharp needle (available through 1 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 rubber.) 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.
This needle is usually available from mailorder magic store dealers such as: Louis Tannen Inc., 1540 Broadway, New York, NY 10036; Al’s Magic Shop, 1012 Vermont Ave., NW, Washington, DC; Perfect Magic, 4781 VanHorn, Suite 206, Montreal, Que. H3W 1J1, Canada. 1
run.
Loading the column with the sample, the smaller beads roll down faster than the larger ones, which need more time to find a way around the table tennis balls. Sometimes a bead is blocked, indicating permanent adsorption, and there is always 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.
An Improved Demonstration of Colloid
Flocculation Submitted by
O. L. Crees Sugar Research Institute MacKay, Queensland, Australia
E. Senogles
An Unusual Demonstration of the Behavior of Gases Submitted
by
Ariel E. Fenster John Abbott College St. Anne de Bellvue, Que., Canada
David N. Harpp
McGill University Montreal, Que., H3A 2K6, Canada
Joseph A. Schwarz
Vanler College Montreal, Que., H3X 2N9, Canada Checked
by
Luther K. Brice Virginia Polytechnic Institute 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 balloon. In order to achieve this, one balloon (it can be some-
James Cook University of North Queensland Queensland, Australia Checked by
Richard F. Jones Sinclair Community 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 juice in sugar mills. The process is distinguished from the coagulation or precipitation effect resulting from the addition of low-molecular-weight electrolytes to colloidal systems. We have found the following demonstration of flocculation highly successful and more impressive than that previously reported.1 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
715
