An Exhibition on Everyday Chemistry Communicating Chemistry to the Public David A. Ucko Museum of Science and Industry, Chicago, IL 60637 Rodney Schreiner and Bassam Z. Shakhashiril Institute for Chemical Education, University of Wisconsin, Madison. WI 53706 The American Chemical Society Chemistry Education Task Force recently reported that "puhlic understanding of chemistry is poor", and that "the puhlic is very much aware that 'chemicals' nollute some nortions of the environment, and very little aware that their-lives are chemical" (I).As an illustration, only 2% of adults in a 48-state survey gave an accurate response to the question, "What is DNA?"; 27% gave a partial definition, while 63% replied "Don't know", and 2% responded "It's a poison" (2). The lack of scientific knowledge and understanding among the general puhlic has been termed "mass illiteracy in the sciences" (3). Science museums provide an important means for enhancing puhlic science literacy (4). They are "contemporary, participatory, informal educational instruments" (5) that emolov exhibits and other techniaues to increase uuhlic unaer&anding of science and technology. The ~ u s e u mof Science and Industry in Chicago is a private not-for-profit institution that is free to the public. I t has been visited by over 125 million people since opening in 1933 and now consistently receive'some four million ;isitors each year. The Museum is the oldest and largest institution of this kind in the United States; it contains about 75 major exhibit halls with more than 400,000 sq ft of exhibits. In addition to increasing puhlic understanding of science, the Museum's informal educational setting serves a role complementary to the formal education provided by schools and colleges. For this reason, teachers, primarily from elementary and high schools, bring approximately 4,000 groups of students each year. The Museum exhibits and demonstrations help motivate students by presenting scientific topics in different and stimulating ways. For example, the exhibit described in this article makes use of chemical reactions, interactive computer and videodisc, videotape, audiotape, fiher optics, historical and contemporary artifacts, graphics, and other techniaues to communicate the suhiect matter in nn exciting manner. Also, thr Musrum provides workshops and educntional materials to help trarhers hring the"handson" nppnmch into their classrooms. A recent addition to theexhthitsat the Museum ofscience and Industry is "Everyday Chemistry", a 2,400-sq-ft permanent exhibit on modern chemistry, which incorporates demonstrations of chemical reactions (6).Although many museums, especially in Europe, have historical collections of chemical artifacts few have participatory exhibits on modern chemistry. One notable exception is the Deutsches Museum in Munich, Germany, which pioneered the display of working chemical reactions in a didactic exhibit that is best suited for chemistry students (8).In addition, the Ontario Science Centre in Toronto, Canada, has developed several exhibit units hased on chemistry. Museum exhibits
(n,
Presented in part at the 189th Annual Meeting of American Chemical Society, Division of Chemical Education. May 1. 1985. Currently on leave to serve as Assistant Director for Science and Engineering Education at the National Science Foundation, Washington, DC.
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that include functioning chemical reactions offer an opportunitv for communicating. chemistry that is unavailahle to mass-media such as tele&ion or magazines because these exhibits offer the immediacy of experiencing chemical change in person. The Exhlblt The exhibit objective is to help the public understand the chemical world that underlies everything around us by introducing basic chemical concepts and their everyday applications. The specific topics presented were selected hased on their imnortance. their relevance. and their ahilitv to he presented in exhibit format. Most of the exhibit units are incorporated into three very large cases. (The exhibit floor plan is shown in Fig. 1.) The following is a summary of their contents. Case /A: If's Elementary This section introduces basic concepts about atoms and molecules. "Ten Little Atoms" uses fiher optics to indicate the locations of electrons within specified regions in atoms of the first 10 elements. "Sticking Together" is a graphic panel that illustrates how two hydrogen atoms chemically bond. "Molecules" compares different ways that molecular models can reoresent water. elucose. and a nortiou of a nolvnentide . ". . (poly-i-serine), ' ' ~ r z k i nApart ~ water" allows the visitor to activate the actual electrolvsis of water and the ignition of the resulting hydrogen and bxygen gas (see Fig. 5)."Why Can We Eat Salt" compares sodium, chlorine, and sodium chloride. A World War I gas mask is part of this display.
Case 16: Properties Here the visitor is introduced to some of the major properties of common suhstances (see Fie. 3). "A Droo of Water" describes the meaning of important physical pioperties by means of a eranhic nanel. "Water Still" is an oneratine: 8~ i t e r - ~ e r - h o~ &a r n s t e a dglass still that illustrates con;ersion of state. as well as produces distilled water for the preparation of exhibit reagents. "Color" shows the variety of colors of compounds bv means of a d i s ~ l a vof 16 samples. "Common ~ r o ~ e r t i e s " " s e examples s oiobjects found b n a kitchen counter to demonstrate the properties of suhstances from the home. Ketchup, for example, is used to illustrate viscosity. "Mix It Up" lets the visitor rotate a cylinder with five immiscible liquids to learn about density. Case llA: Reactions In this section, the visitor learns about chemical changes and enernv bv activatinn examoles of different tvnes of react e s liphi ;.an be protions. ..C'hemical ~ i ~ h ~ " d r m o n s r r a that duced hs a chrmical reactiun, ns in a firefly. Thechemiluminescenck reaction used is the oxidation of luminol (see Fig. 4). "A Light Reaction" shows how the energy from light results in a chemical reaction, in this case, the bleaching of thionin. Reference is made to photosynthesis. "Current Reaction" shows the creation of an electric current form the chemical reaction in a copper-zinc voltaic cell. "Hot Reaction" allows visitors to feel the heat generated in aflask from Volume 63 Number 12 December 1986
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F
The ElementE
I
Whar's New
L I
Everyday Chemistry Figure 1. The exhibit floor plan
Figure 2. 'Breaking Apart Water
Figure 4. "Chemical Light"
Figure 3. Case iB, "Properties"
an exothermic reaction, the neutralization of sulfuric acid' and sodium hydroxide. "Everyday Reactions" is a display that shows objects that illustrate familiar chemical changes from around the house. Examples include matches, yeast, drain cleaner, bleach, antacid tablets, tarnished silver, rusted metal, and meat te1,derizer. "Changing Partners" is a graphic panel that describes how chemical reactions take place. 1082
Journal of Chemical Education
Case 11B: Acid or Base?
These sections introduce visitors to the properties of acids and bases and to chemical analysis. "Acids and Bases" displays everyday . . examples from battery acid t o lye on a pH kcale, along with iirn1;lr pH tc,sting r&ipment. idjaceni to rhedisplay is ademomtrdtion that nllou.s visitors to tirrare a vinegar sample while watching an indicator and pH meter change. "Chemical Puzzle" is based on the modification of an interactive videodisc developed by David W. Brooks and the University of Nebraska Videodisc DesignIProduction Group. In a simple case involving four reagents (acid, silver ion, chloride ion, carbonate ion), visitors can determine the
Figure 5 'The Elements'
identity of chemical unknowns after observing knowns.
What's New?
Case IllA: It's Organic
This section, which opened with a description of Nobel Prize-winning work on prostaglandins, is a unit that is updated annually to reflect recent developments in chemistry.
Here the visitor learns about basic and applied organic chemistry. "Chemistry of Carbon" is a graphic panel that describes the central role of organic chemistry in life and industry. "Chemistry Smells" lets visitors try to match the odors of four organic compounds (acetic acid, methyl salicylate, limonene, and cinnamaldehyde) with brief identifiers. "Polymer Balls" demonstrates the difference in bounce of two balls made from different chemical formulations of Norsorex (CDF ChimieBEG Associates), a polynorhornene. One ball has 50% rebound while the other has zero rebound. "Polymers" shows common examples, including polyethylene, polyester, nylon, polystyrene, and polytetrafluoroethylene. "Chemical Industry" features a brass model of a Danish distillery from the 1930's, a gift of the Royal Danish government to the Museum and part of its collections. "Chemical Drugstore" displays early and modern examples of actual pharmaceuticals and over-the-counter preparations.
The adjoiningsrairwell to the exhibit containsa 40-ft-high spiral version of the periodic tahle (91.A s shown in Fieure 6. i t consists of a helix with three sizes of revolution thatieflect periods of different length. Each element is represented by a panel with its name, symbol, and atomic number; elements in the same group are vertically aligned and color coded.
Case 11iB: Living Chemistry
The Automated Chemlcal Demonstratlons2
This section introduces baaic concepts related to the chemistry of living things. "Biochemistry" provides a graphic overview of chemical changes within the body. "Proteins" and "DNA: Molecule of Life" are graphic panels that describe the biological roles of these macromolecules. "The Body Chemical" displays simulated samples of key chemicals found within the body. "Chemical Breakfast" illustrates by means of a three-dimensional breakfast display the many chemicals naturally found in foods. "Chemical Feast" is a videotape that presents a humorous look a t modern chemistry.
"Everyday Chemistry" generates interest in and communicates aspects of chemistry by presenting i t in a fascinating way to large numbers of people. The strength of the exhibit is its ability to let visitors experience actual chemical demonstrations. These reactions also make i t one of the most tech-
The Elements
This 30-ft-long display, shown in Figure 5, presents samples of the elements and their uses. This large case contains 219 samples (68 elements, 151 uses), in addition to 24 photographs. Visitors can learn interesting facts about each maingroup and transition element while listening to Tom Lehrer sing "The Elements". Examples of common ores in which elements are found are displayed also. Periodic Table of the Elements
> The description of the automated demonstrations presented here
is not intended to provide complete specificationsof the mechanisms
and their operation. Those who desire further details should contact David Ucko at the Museum of Science and Industry. Volume 63
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December 1986
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ment no more than twice weekly. Furthermore, the reagents are stable for at least a week. To minimize costs, the chemicals used are relatively inexpensive and readily available. For ease of maintenance...nrenaration of the reaeents is sim. " ple and allows for a margin of error. The mechanical devices that were developed to present the demonstrations based on these criteria have certain features in common. First, each demonstration is controlled by a microprocessor, which operates the graphic indicators and monitors the visitors' i n ~ uas t well as controlling the mechanism of the demonstracon. Second, all the demonstrations are activated by a "two-touch" system to ensure that the demonstration is presented only for a visitor who is interested in seeing it. Upon the first touch of the activator, a zrauhic - . nanel liehts descrihine the demonstrations. Shortlv thereafter, another panel lights telling the visitor to touch the activator again to see the demonstration. If the activator is not touched while the second panel is lit, the demonstration is not ~resented.Third. for the sake of durabilitv. those portions oithe device which come in contact with c h k c a l s are constructed of heavy-walled glass, of high-density polyethylene or polypropylene, or of solid Teflon. The mechanism and chemical operation of the demonstrations can be considered in three groups: closed systems, nearly closed systems, and open systems. The closed systems consume no chemicals and produce no wastes; the nearly closed systems consume very little and produce virtually no waste: and the onen consume a sienificant amount . svstems . " of reactants and produce an equivalent amount of waste with each oneration of the demonstration. The comnlexitv of the mechanism and the amount of maintenance increases in the order: closed, nearly closed, and open. The immiscible liquids demonstration ("Mix I t Up") is one of the closed systems. In this unit, five liquids are displayed in a large glass cylinder. Because the liquids are immiscible, they separate into five layers. When a visitor activates the demonstration, the cylinder is inverted, disturbing the liquids, which nevertheless settle hack into their original layers, illustrating the effects of the property of density. The liquids used are mineral oil, water, bis(2-chloroethyl)ether, fluorocarbon oil, and mercury. Photochemical bleaching ("A Light Reaction") is the other closed system. When aspot of bright light from a projector shines on a thin tank of blue liquid, the hlue liquid is bleached to colorless (11). When the light is extinguished, the blue color gradually returns. This demonstration illustrates that light can cause chemical change. The hlue liquid is a dilute soiution of sulfuric acid containing thionin (a blue dye) and iron(I1) sulfate. Thionin is an oxidizing agent, but is not powerful enough to oxidize iron(I1). However, as its color indicates, thionin absorbs visible light energy, and when it does so, i t becomes a more powerful oxidizing agent, capable of oxidizing iron(I1) to iron(II1). The reaction can be represented by A
Figure 6. "The Periodic Table'
nically complex exhibits a t the Museum of Science and Industry. Because observations and experiments are the foundations of chemistw. observation of actual chemical reactions is a fundamentalpart of the "Everyday Chemistry" exhibit. Museum visitors are " eiven the onnortunitv to observe actual .. chemical reactions as they occur. T o allow the individual visitor to observe a chemical reaction a t anv time. these demonstrations are presented by visitor-activated, mechanical devices that were developed for each reaction a t the University of isc cons in- ad is on. These experiments are intended to help provide the "concrete observational experience" necessary for cultivating science literacy (10). Each of the devices for presenting a chemical demonstration was designed specifically for this exhibit to meet the unique requirements of the museum setting, which creates a number of soecial demands. First. because visitors can activate the de\,ires at any rime, each devire must provide its reartitm on demand. Second. hecause thc exhihit is intended to be a long-term display, thk devices must survive for years before requiring replacement of major parts. Third, because the exhibit is maintained by personnel with only limited training, the devices must be serviceable by a technician with no specific knowledge of chemistry. Fourth, because each device is composed of a variety of components, any one of which may fail to operate properly, each must operate with a fail-safe system. If any component should fail, the device must not be damaged, nor may a hazardous condition result. The reactions used in the demonstrations were selected not only for their suitability to the content of the exhibit but also to fit the limitations of their setting in a museum. To hold the interest of the visitors, each reaction must begin soon after the device is activated by the visitor. Therefore, very slow processes or reactions with long induction times are not used. T o minimize d i s ~ o s a problems l and to avoid the need for special venti1ation;no highly corrosive, toxic, or volatile materials are used. For this reason, substances such as lead compounds and organic solvents have been avoided. To minimize maintenance, the reagents require replenish1084
Journal of Chemical Education
thionin(oxidized) + Fe(I1) (blue)
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thionin(redueed)+ Fe(II1) (colorless)
When the blue, oxidized form of thionin absorbs light, i t oxidizes Fe(I1) to Fe(II1) and is itself reduced to its colorless form. In this way light causes the solution to bleach. When the lieht is extineuished. the reaction reverses and the blue color returns. One of the nearlvclosed svstems is the electrochemical cell ("Current ~eaction"). his-large gravity cell (12) contains a deer, hlue, saturated solution of copr,er(II) sulfate in the bottom of a large glass tank with a copper plate suspended in it as the cathode. T o keep the solution saturated in copper sulfate, the bottom of the tank is covered with a layer of &lid copper sulfate. Floating on the dense copper sulfate solution is a~colorless,dilute s&tion of zinc sulfate. In a standard gravity cell, a solid zinc electrode suspended in the zinc
sulfate solution is used as the anode. Because the zinc dissolves as the cell onerates. the zinc electrode must be replaced periorlicnlly.'1'~1eliminatethe necessity of fabricating reulacement electrodes. the anode in the exhibit cell is made ofstainless steel screen on which zinc bars are resting. The zinc bars still dissolve. but thev can easilv be renlaced with commercially available bars as needed. Through cathodic protection, the zinc prevents the steel from corroding in the cell. The cell is designed so that it can operate a long time before it requires addition of more zinc, and an even longer time before it needs to be disassembled to replenish the copper sulfate. That electrical energy can be obtained from this arrangement of chemicals is demonstrated by connecting the anode and cathode of the cell to the terminals of a motor, which turns a propeller when connected. The connection is made when the visitor touches the activator. The other nearly closed system is the electrolysis of water ("Breaking Apart Water") shown in Figure 2. The setup is essentially a Hoffman apparatus having two vertical gas collecting tubes joined by a bridge which is connected t o a reservoir (out of view). The electrodes are a t the bottom of the tubes, and at the top of each tube is a valve, which is normally closed. After the visitor activates the device, a voltaae is amlied to the electrodes. and the water is decomposed into its elements. ~ ~ d r o g e n ' c o l l e cin t s one tube and oxygen in the other. The visitors can see that the volume of hydrogen generated is twice that of the oxygen. A small polyethylene ball floats on top of the water in each tube, and, as the gas is generated, t h e ball descends with the water level. Eventually the ball hreaks an infrared beam, signalling the microprocessor to turn off the voltage to the electrodes. As a fail-safe system, if the infrared detector should fail, the microprocessor will also shut off the voltage after a measured time interval. If the microprocessor itself should fail and the voltage is not turned off, the water level will fall to below the electrodes and electrolysis will cease, thereby avoiding the production of a dangerous amount of hydrogen. A few seconds after the voltage is removed from the electrodes, the valves a t the top of each tube are opened and the water (seeking the level in the hidden reservoir) forces the gas out of the collecting tubes and into a glass cylinder above the apparatus. At the-top of the cylinder is spark plug. After a short pause, a spark chamber ignites the hydrogenoxygen mixture in the cylinder. The explosion produces a loud bang, and a film of water mist forms on the inside of the cylinder. Thus, in this demonstration, the compound water is broken into its elements and these elements are recombined into their compound. Because the electrolysis consumes very little water in each cycle, the water needs to be replenished only occasionally, and this can be done simply by adding water to the reservoir. The open systems, exothermic reaction ("Hot Reaction"), chemiluminescent reaction ("Chemical Light"), and titration ("Acids and Bases") are by far the most mechanically complex of the demonstrations. These three consume reagents in each cycle and produce waste that must be removed. Each one mixes two or three solutions t o produce a mixture with a volume of about 60 mL. In accomplishing this, these devices emdov a number of similar comnonents. The solutions in eacl; are contained in 20-liter reservoirs from which thev are dispensed bv comoressed air. The compressed air operates a-dispensing device designed at the Deutsches Museum in Munich (8).This device consists of two concentric tubes, the outer of which is enlarged into a bulb a t the bottom, which has aone-wascheckvalve oveninn into it. At the top, the outer tube is connected to valve controlling the compressed air line, and the inner tube leads to the front of the exhibit. When the dispensing device is placed in the reservoir, the air is disconnected and the solution flows through the check valve filling the bulb. When the compressed air valve opens, the interior of the dispensing
a
a
device is pressurized. The liquid cannot escape through the one-wav valve. and instead is forced throueh the inner tube to the iiont of thedisplay. When the levrl (,'?the liquid in the hull1 falls to the bottum of the inner tuhe. the cumuressed air flows through the inner tube to the display, a& no more liquid is dispensed. When the compressed air is turned off, the solution in the reservoir can again flow through the oneway valve into the bulb. Through an adjustment of the level of the inner tube in the bulb, the volume of liquid dispensed can be adjusted. Furthermore, the dispensing device serves as its ownfail-safe system; if the comprissed & valve should fail in the open position, the device would dispense only its set amount of solution and no more. This avoids the nrohlem that would arise if a pump were used to dispense t h l liquids and the pump failed or if a valve were used to meter the volume of solution and that valve failed. Other features common to the open systems include a rinse cycle and overflow channels. Because some time may elapse between each operation of the device, the solutions could dry onto the apl)iratus and clog the tuhing or valves. To prevent this, a rinse of distilled water is sent through the apparatus after each demonstration cycle. Furthermore, this distilled water rinse, and the wasre solutionsas well, must be drained. If the val\.eu contndline the drains should fail. the solutions could overflow into tce exhibit. Therefore, ail of these open systems have overflow channels that carry any excess liquid directly to the drain. When a visitor activates the chemiluminescence demonstration shown in Figure 4, a colorless solution and a blue solution are dispensed into a coil of glass tubing where they mix. The lights of the apparatus are extinguished. A blue glow fills the coiled tube as the mixture runs through it. By the time the mixture has reached the bottom of the coil, the glow has faded to where it is barely visible. The reaction in this demonstration is the oxidation of luminol (3-aminophthalyhydrazide) by hydrogen peroxide (13).o n e of the products of the reaction is formed in an electronically excited state, and this excited state decays to the ground state by the emission of visible liaht. The comnonents of the oroduct mixture are inuocuous,and the mixture is allowed-to flow out the bottom of the coil directly into the exhibit drain system. The exothermic reaction demonstration uses the reaction between dilute sulfuric acid and a solution of sodium hydroxide. When the visitor activates the demonstration, about 30 mL of each of these solutions is dispensed into two small cylinders containing thermometers. These thermometers indicate that the solutions are a t room temperature. Then, the solutions flow into a round flask that also contains a thermometer. The visitor can watch as the thermometer registers a 30 to 40 O C increase in the temperature of the mixture. Furthermore, the front panel of the display is cut away so the visitor may place several fingers onto the round flask and feel that it is indeed warm. After the reaction is complete, a valve a t the bottom of the round flask opens allowing the solution of sodium sulfate to flow into the drain svstem. The titration demonstration is the most complex of the demonstrations, both conceptually and mechanically. The apparatus consists of two burets, one filled with vinegar (dilute acetic acid) and the other with dilute sodium hvdroxide solution. ~ e t w e e nthe burets is a dispenser for [he pH indicator, metacresol ournle. Below these is a beaker containinga ~nag!ieticstir'har.~nda pH electrode.Tu the left isa pH mrrerand ru the right adiritald~solavfor indicating the iolume of sodium hydroxide that has flowed from the k r e t during the demonstration. When the demonstration is activated, the distilled water that keeps the pH electrode moist is drained from the beaker, and a preset amount of vinegar is dispensed from the buret into the beaker. Then, several drops of indicator are added, and the stirrer is started. The Volume 63 Number 12 December 1986
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visitor can see that the indicator turns the solution yellow and that the pH meter registers a pH of about 3. Then, by touching the activator, the visitor can add an aliquot of sodium hydroxide from the other huret. The digital display indicates the volume added, and the pH meter shows the effect this has on the value of the pH. The visitors can add more sodium hydroxide by repeated touches of the activator. Each touch dispenses a predetermined amount of sodium hydroxide, and the amount becomes smaller with each touch, so it is very easy for the visitor to neutralize the vinegar without going far beyond the equivalence point. As the solution approaches neutrality, the visitor can see that small amounts of sodium hydroxide have a great effect on the pH as shown on the meter, and that the color of the indicator changes from yellow to purple. The visitor may add sodium hydroxide t o beyond the equivalence point if desired. However, when the pH of the solution reaches 10, or when the activator has not been touched for about a minute, the rinse cycle begins, and the device will prepare itself for the next demonstration. Because of the success of the exhibit, it is currently being expanded. A new experiment, an oscillating reaction, is heing added to the "Reactions" case. A demonstration device to show the effect of an emulsifying agent on two immiscible liquids will he added to the "Properties" section. A videotape on chemical production is heing made for "It's Orgauic". The "What's New?" section is heing upgraded to include acase for objects and images, with a microcomputer that will
1086
Journal of Chemical Education
provide further information about any of them. Additions such as these will be an ongoing process that will keep the "Everyday Chemistry" exhibit an exciting experience for millions of visitors for years to come. Furthermore, we hope that it will serve as an invitation and an inspiration for other science educators interested in exploring ways to enhance public understanding of chemistry. Acknowledgment
The creation of "Everyday Chemistry" was made possible by a generous grant from the Regenstein Foundation. We wish to thank the Foundation for its continued support to the Museum. Llterature Cited 11) "Tomorrow. Tho Report of the T a k Force for t h e Study of Chemistry Education in the United States"; American Chemical Soeiafy: Washington, DC. 1984: pp v. 10. (2) Science Neui. 1983.12:3,366.
[a! crauhard, stephenR.~ ~ . d & 1983.r12.231. r (4) Ueku, David A. Cumlor 1985,28,287. (5) Oanilov, Victor J."Seienee and Technology Centers":MIT: Cambridge, 1982; p 2. (6) Chem. En& News 198462(251.18.
(71 Van Spronsen. J. W."A Guide of European Museums and Expositions of Chemistry and History of Chernistcy': Museum for Science and Technolagy: Budapest, 1981. 181 Krstz, Von MtoP.; ProbP~k.Glmther; Dietrich. Stephsn.Chem. Exp. Didokt. 1975.
7 ma ., (9) Marun,E.G."GrsphicR~presentatiansofthePeridicSy%temDuringOneHundred Years"; University of Alabama: University. AL, 1975: type LA3~2. (10)A m m , A. B. Doodolus 1983,112.91. (111 Heidt,L. J. J. Chem.Educ. l949,26,525. (12) Shakhashiri. Bessam 2.:Dirreen, Glen E. "Manual far Lsborafon, Investigation8 in General Chemistry"; Stipes: Champaign, lL 19RZ; p 169. (13) shnkhsrhiri, Bassam 2. "Chemical Demonsfretion: A Handbook for Teachers o+ Chemistry": University of Wismnsin: Madinon, WI, 1983: p 156.
