parenthesis: 1720 (126) and 1170 (86). We have repeated the measurement several times and have obtained good reproducibility and good accuracy, that is, the pressures agreed with clinical values.
I t also was a convincing demonstration of the varying oxidation states of the transition metals with Cr(VI) (orange-red) in the same test tube with CdIII) (green). Good demonstrations can speak louder than lectures!
Discussion The seismic detector replaces the conventional stethoscope that is ordinarily used in blwd pressure measurements. The detector contains a magnet, which is suspended by a delicate spring inside a coil of wire. Motion of the magnet creates a small voltage, which can be amplified and ultimately heard. This type of device is used to monitor earthquakes, oil exploration, and almost any other type of motion. The blood pressure in units of millimeters of Hg can be obtained bv dividine the millimeters of H.0 bv 13.6. No hazardous or ~oisonou~chemicals are used in this demonstration and no waste disposal problem is created.
Literature Cited
Classroom Demonstration of Chromium(VI)IChromium(lll) in the Breathalyzer Test Reaction
Checked by Joseph H. Dreisbach University of Scranton Scranton, PA 18510 I have taught a chemistry course for nonscience majors for several years and am always looking for ways to stimulate the interests of my "anti-science" students. Everyday applications and classroom demonstrations have proven to be the most popular avenues used in the course. A recent demonstration and application proved most successful. Sulfuric acid (6M, 100mL) was combined with KzCrz0, (O.lM, 8mL) in a large, demonstration-size, test tube. Ethyl alcohol (10mL) was slowly added to this orange-red solution, creating a green layer in the top half of the test tube if left undisturbed. This reaction captured the interest of my students because it is the reaction involved in a breathalyzer test (I). 8Ht + C ~ ~ +O 3C2H50H , ~ + 2cr3+ + 3C2H40+ 7Hz0 diehmmatc im ehmmiumim~irn iwn1
(orange-redl
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////////////////////////// TOP OF OVERHEAD PROJECTOR Schematic sectional view of aooaratus ~ , ~for ,dernonstratina ~ ~ " fluid flow as a res~ltof tne acnon of a magnetc Iiea on an ionic current. 2 : zinc rod; C copper rmg an0 connecting ware, A: 01Jte acid: P: Petn dlsn: S: support; M: bar magnet. ~~~~~~
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Submined by
Ian M. flitchiel School of Mathematical and Physical Sciences Murdoch University Murdoch, Western Australia 6150
Checked by Daniel Hawolth Marquette University Milwaukee. WI 53233
Rebecca 0. Jones University of North Carolina Wilmington, NC 28403-3297
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Classroom Demonstration of Fluid Flow as a Result of an Ionic Current in a Magnetic Field
Gregory P. Power Alcoa of Australia Pty Ltd Kwinana, Western Australia 6167
Submitted by
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1. Hill, John W. Chemislryfw Cho'~ging 2Imes;Macmillan: New York, 1992, p 244
Journal of Chemical Education
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I t is well-known that when a current of electrons is passed through a wire in a magnetic field perpendicular to the wire. the wire moves in a direction a t rieht aneles to both thecurrent flow and the magnetic field. The direction of movement is rziven bv Lenz's left-hand rule. This ohenomenon was ofiourse first discovered by Faraday &d it forms the basis of the electric motor. Most frst-year physics texts give a reasonable account of this topic. It is less well-known that the same phenomenon can be observed when an ionic current is passed through a solution, the current being perpendicular to a magnetic field. So far as we have been able to establish, the first person to demonstrate this phenomenon was Blaha (I).He made use of the fact that the ionic current that is passed during the corrosion of a piece of iron under the surface of a drop of aqueous potassium chloride solution is radial. The current flows from the anode a t the center of the drop where iron is dissolving to the cathode at the perimeter of the drop where oxygen is being reduced. If the corroding iron is placed between the poles of a magnet, the drop rotates. However, the rotating drop cannot be seen by more than a few students and is therefore unsuitable for a class demonstration. To overcome this difficulty, the following variation, which can be readily shown on a n overhead projector, has been devised. A cross-sectional view of the apparatus is shown in the figure. The corroding metal is a zinc rod Z, which must be made of sufficient purity for the zinc to not corrode rapidly in dilute acid. A tube of zinc sheet is equally satisfactory, but doesn't last a s long. The zinc rod is connected a t its upper end to a copper ring by a copper wire C. The copper ring and wire should be thick enough to give the structure reasonable rigidity. Before use, both the lower end of the zinc' rod and the ring should be cleaned with emery paper. In order to obsewe fluid flow in the presence of a magnetic field, the lower end ofthe zinc rod and the copper ring are placed in the Petri dish P (approximately 10 cm in diameter is suitable) and just covered with dilute acidA(2 M sulfuric acid is suitable). The zinc dissolves Znbq) + 2nZ++ 2e 'Author to whom correspondence:should be sent
