oh,the joy of toys! - max studymaxstudy.org/chemistry/honors/wpcp_008052.pdfoh,the joy of toys! ®...

®

OCTOBER 2005

Discover Chemistry in theAmazing Drinking Bird

OH,THE JOYOF TOYS!

OH,THE JOYOF TOYS!

®

Vol. 23, No. 3 OCTOBER 2005

ChemMatters, OCTOBER 2005 3

Production TeamKevin McCue, EditorCornithia Harris, Art DirectorLeona Kanaskie, Copy EditorChristen Brownlee, Contributing Editor

Administrative TeamHelen Herlocker, Administrative EditorSandra Barlow, Senior Program AssociatePeter Isikoff, Administrative Associate

Technical ReviewSeth Brown, University of Notre DameDavid Voss, Medina High School, NY

Teacher’s GuideWilliam Bleam, EditorDonald McKinney, EditorSusan Cooper, Content Reading ConsultantDavid Olney, Puzzle Contributor

Division of EducationSylvia Ware, DirectorMichael Tinnesand, Associate Director for AcademicPrograms

Policy BoardDoris Kimbrough, Chair, University of Colorado–Denver Ron Perkins, Educational Innovations, Inc., Norwalk, CTBarbara Sitzman, Tarzana, CA Claudia Vanderborght, Swanton, VT

Frank Purcell, Classroom Reviewer

ChemMatters (ISSN 0736–4687) is published five times ayear (Sept., Oct., Dec., Feb., and Apr.) by the AmericanChemical Society at 1155 16th St., NW, Washington, DC20036–4800. Periodicals postage paid at Washington, DC,and additional mailing offices. POSTMASTER: Sendaddress changes to ChemMatters Magazine, ACS Office ofSociety Services, 1155 16th Street, NW, Washington, DC20036.

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Question From the Classroom

What makes a Superball so super? 4

ChemSumerLiquid Crystal Displays 6The color screens on portable electronic gadgets are better andcheaper than ever before. Oh, the joy of toys!

The Amazing Drinking Bird! 10It’s fun. It’s frivolous. It’s the avian wonder whose insatiablethirst is driven by the cooling “power” of evaporation.

Kitty Litter Chem 12Scoopable cat litters make cleaning up after your cat sheerunadulterated joy. Yeah right! Still, superabsorbent clay isbetter than the sand or ashes of a generation ago.

ChemHistoryThere’s Chemistry in Golf Balls! 15

Aerodynamic dimples. Vulcanized synthetic rubber. Complexdesign and materials. There’s a lot of science packed in thoselittle white balls.

Interview With a Chemist 18Meet a chemist whose mission is to save lives in theevent of a chemical, biological, or radiological attack.

Chem.matters.links 20

COVER PHOTOGRAPHY BY MIKE CIESIELSKI

Correction:David Holzman (not Holtzman) was the authorof our February 2005 article “Water of Life”.

PHOTOS COURTESY OF ERICK SWARTZ

MIKE CIESIELSKI

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Q: What makes a Superball so super?

A: The original Superball “fact sheet” published by

Wham-O in 1965 said the Superballs were made of an

exotic new compound called “Zectron”. That sounds pretty

futuristic and high tech, but it means nothing to a chemist.

The patent for Superballs, however, filed by its inventor Norman

Stingley in that same year, lists as its main ingredient a well-known

polymer known as polybutadiene, a name that does mean something to

chemists. The prefix “but-” means a four-carbon chain. The “-ene” end-

ing means double bond, and “di-” means two. So “butadiene” means a

four-carbon chain with two double bonds: CH2=CHCH=CH2

Finally, the prefix “poly-” means that many of these butadiene mol-ecules are strung together. The stringing together (aka: “polymeriza-tion”) of these butadiene units starts with a free radical—a moleculewith an unpaired electron, and hence an open bonding site. The way apolymer chemist represents the overall reaction is:

The “n” represents a largenumber, often in the thousands.The fact that there are still dou-ble bonds in the polymerchains is very important, for itallows the polymer chains tobe “vulcanized.” Vulcanizationis a process discovered andpatented by Charles Goodyear in1839. Rubber at that time was verylimited in its uses. In the summer time, itgot soft and gooey, and in the winter time it became hard and brittle.Goodyear discovered that if you added sulfur to the rubber, and sub-jected it to heat and high pressure, it made an all-weather rubber thatremained flexible and resilient year-round. The sulfur atoms form little

bridges between the polymer strands (at thedouble-bond locations) which kept thestrands from sliding past one another athigh temperatures or contracting into knotsat low temperatures.

Apparently, when polybutadiene is vul-canized at a temperature of 160 °C and a pres-

sure of 70 atm (according to Stingley’s patent), itcreates a cross-linked polymer with a resilience of

92%. This meant that if you dropped a Superball from 100.0 cmonto a hard surface, it would bounce back to about 92.0 cm, then 84.6cm, then 77.9 cm, and so on, always bouncing to about 92% of its pre-vious height. When many elastic substances are distorted, they regaintheir original shape, but in the process, some of the energy that wentinto distorting the substance is lost as heat. If it didn’t, you could theo-retically produce a Superball that would bounce forever (ignoring airresistance). Anyone who has played squash or racquetball is familiarwith how the ball heats up the more it is bounced. Vulcanized polybuta-

diene only loses 8% of its energy to heat per collision, and there-fore bounces back with 92% resiliency. This was much more than

any bouncing ball manufactured at that time.This alone was impressive,

but it alone would nothave made theSuperball thehottest sell-

ing toy of themid-1960s. Asecondremarkableproperty ofStingley’s“Zectron”was its highcoefficient offriction. Trypulling a Super-ball across asmooth surface, andyou will appreciate thiseffect. When bounced

4 ChemMatters, OCTOBER 2005 http://chemistry.org/education/chemmatters.html

By Bob Becker

Question From the Classroom

SUPERBALLFACTOID

As a promotional item, Wham-Oonce built a giant Superball, whichwas accidentally dropped out of a 23rdfloor hotel window in Australia. It shotback up 15 floors, then down againinto a parked convertible car. The

car was totaled, but the ball sur-vived the "test" in perfect con-

dition.

C

CH2CH2

H

CH2

H H

H

C CH

HC

C CH

HH

C CH

CH2

n

2n

Addition Polymerization


across the floor to a friend, the first bouncecauses the ball to acquire a significant topspin. Thistopspin then propels the ball with remarkable speed on the secondbounce, making it nearly impossible to catch. This high coefficient offriction also allowed for all kinds of tricks, the most famous of thembeing the under-table bounce: If the ball is bounced off the floor so thatit hits the underside of a table, the aforementioned topspin makes theball rebound straight back to thethrower. If you have never seenthis, give it a try.

polymer chains

cross linksss

ss

Challenge:Can you match these toys with

the years they first hitthe stores?

___ Frisbee A) 1945___ Hacky Sack B) 1948___ Hula Hoop C) 1955___ Slinky D) 1958___ Slip ‘n Slide E) 1965

___ Superball F) 1983

Find the solution on back page.

In the vulcanizedrubber of a Superball,polybutadiene strands

are partially cross-linked with

sulfur atom bridges.These bridges keep

the strands from sliding past oneanother at hightemperatures or

contracting into knotsat low temperaturesand make the ball

very resilient.

http://chemistry.org/education/chemmatters.html6 ChemMatters, OCTOBER 2005

Do you enjoy

photo- and

instant-messaging

with your friends,

watching fast-

action sports on a

widescreen TV,

playing fast-action

games on a Game

Boy, or viewing

DVDs? If so, your

fun is made

possible by LCDs.

By Lois Fruen

L


LLCDs, or liquid-crystal displays,are everywhere; they are in cellphones, laptop computers,games, MP3 players, and all man-ner of electronic devices. They arethin and lightweight and are run

on little power. But what is it about liquidcrystals that make all this possible?

Order in disorderThe name liquid crystal sounds like an

impossible contradiction. Liquids can flowand crystals are solid. How can there be a liq-uid crystal? In a normal crystal, the mole-cules have an orderly arrangement. In aliquid, the molecules are jumbled and disor-dered. Liquid crystals, on the other hand,have molecules that can flow, but that alsohave an orderly arrangement.

There are several types of liquid crystals,but all of them contain molecules that are lin-ear and polar. Linear molecules have atomsarranged generally along a line, so they areconsiderably longer than they are wide. Apolar molecule is one in which the electronsare distributed unevenly, leaving certainregions with a slight positive electrical chargeand other regions with a negative charge. Thecharges make the ends of the moleculesbehave somewhat like the poles of a magnet,and the molecules are attracted to each other.If the molecules have a suitable shape, theywill line up. No permanent attachments areformed between molecules, so the materialdoes not solidify.

Liquid crystals are typically long, thinorganic molecules that change orientation inan electric field. The most common type ofliquid crystal is the nematic liquid crystal.More than 50,000 different liquid crystals areknown.

Pixels and subpixelsThe real secret behind a flat-screened

LCD television or fast-action handheld gamescreen is the liquid crystals that are sand-wiched between the polarizing films. Tounlock that secret, we need to investigate howpolarizing films work. The films are positionedat 90-degree angles to each other so that lightpolarized by the first film is blocked by thesecond. This results in a black spot.

If the top polarizing film is rotated 90 degrees, light passes through both.

Because it’s impractical to physically rotatethe polarizing films, chemists have synthe-sized nematic liquid crystals that rotate polar-ized light in response to voltage changes. Theultimate role of the liquid crystal and polarizedfilm combination in an LCD is to quickly blockor allow light through a subpixel.

What is a subpixel? If you take a reallyclose look at an LCD screen, you will see indi-

vidually colored regions called subpixels.Three successive subpixels—one red, onegreen, and one blue—make up a pixel on yourdisplay screen.

An elaborate series of electronic transis-tors and capacitors are deposited onto glassplates. Color filters are added in alternatingprimary colors of red, green, and blue. Atransparent indium tin oxide layer is depositedon top of the transistors, which serves as anelectrode for each of the glass plates. The topand bottom plates are then glued togetherleaving a small hole to a gap where the liquidcrystals are filled using a vacuum process.Very large-sized monitors and LCD TVs usemore sophisticated manufacturing processes.Finally, the glass plates with the liquid crystalsand electronic components are sandwichedbetween the two polarizers that are oriented at

90-degree anglesto each other.

When volt-age is applied tothis blue subpixel,the nematic liquidcrystal moleculesuntwist and lineup with the elec-tric field, lettingpolarized lightthrough to thesecond polarizerthat absorbs thelight. No light istransmitted to the

screen so the subpixel looks black.When the voltage to a subpixel is off, the

nematic liquid crystals relax back to their orig-inal twisted state. Incoming polarized light fol-lows the twist of the liquid crystal molecules,rotating 90 degrees, enabling it to passthrough the color filter and on through thesecond polarizer. With a red filter, red light istransmitted by the subpixel.

indium tin oxide grid

green subpixel

red subpixel

pixel

Three successive subpixels—one red, one green, and one blue—make up thepixels of your display screen. The subpixels shown are about 0.20 mm wide.

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Liquid crystals are often composed of longmolecules with a dipole moment typically parallelto the long axis. The molecules of nematic, orthreadlike, liquid crystals do not occupy fixedpositions. However, they tend to lie parallel to oneanother, each pointing in the same direction.

When voltage is applied to the blue subpixel, liquid crystal molecules line up with the electric field. Thisalignment lets polarized light through to the second polarizer that absorbs the light. This causes thesubpixel to look black.

prismatic films

white light

polarizing filtercolor filter

electric fieldliquid crystals line up with the electric field

No light is trans-mitted to thescreen and thesubpixel looksblack.

polarizing filter

blue subpixel

http://chemistry.org/education/chemmatters.html8 ChemMatters, OCTOBER 2005

Mixing light from various subpixelsin a given pixel produces secondarycolors. Red and green produceyellow light. Blue and greenmake cyan, and red and blueresult in magenta light. Whencombined, light from all threesubpixels in a single pixel pro-duces white light.

When mixed, red and greenlight makes yellow light, blue and greenlight produces cyan, and red and blue lightgives magenta. When combined, red, greenand blue produce white light.

By varying the voltage that regulates thepositions of the liquid crystals, shades ofcolor can be produced. Today, a typical 12- or 15-inch laptop screen has 1024 pixelsacross and 768 pixels from top to bottom,which means there are 2,359,296 subpixelson the screen that can produce millions ofshades of color.

Quicker and brighterA big problem with LCD technology used

to be “switching speed”. Switching speed isthe time it takes nematic liquid crystal mole-cules to switch from twisted to aligned stateand back. Historically, liquid crystal switchingtimes were about 25 milliseconds. Improve-ments to the liquid crystal molecules them-selves as well as changes to the electronicdriving schemes have reduced switchingtimes to 8 milliseconds and less. Fasterswitching times have eliminated the washed-out visual smears that plagued action videogamers and DVD enthusiasts who did not likeshadow trails on fast-paced scenes.

In addition, LCD displays haven’t alwaysbeen so vibrant and bright. Newer displayson portable game players and laptops ofteninclude one or two brightness-enhancingfilms in the subpixel. What are they? To

understand them, it helps tolearn a little more about thetiny fluorescent tube indevices that provides the lightand ends up going through thesubpixel.

When switched on, gas inthe fluorescent tube gives offultraviolet (UV) light with shortwavelengths between 365 and366 nm. When the UV lightstrikes a fluorescent coating onthe inside of the glass tube, itexcites electrons in the fluores-cent coating that return to“ground” state, emitting longer

wavelengths of visible light ranging between380 and 760 nm. Chemists have carefullyselected coatings that emit red, green, andblue light, which collectively appears white tothe eye.

The white light from the fluorescent tubeenters the screen along one edge of the lightguide and is scattered by thousands of whitedots on the backside of the backlight panel,directing the light toward the viewer. Bright-ness-enhancing prismatic films refract the

n increasingly popular choiceamong widescreen enthusi-asts are the new plasma tele-visions. Unlike LCD displays,

plasma displays do not use liquid crystals ora backlight. Instead, the display panel on aplasma TV is made up of thousands of tinyphosphorescent cells that are sandwichedbetween two plates of glass. The glass platesand the electrodes between them act as

capacitors and separate thecurrent that activates thephosphorescent cells. Thephosphorescent cells arefilled with neon, xenon, orargon gas and are coatedwith different phosphorescentchemicals called phosphors.Color is produced on aplasma screen when atoms ofthe gas in the tubes areexcited by electric current andemit UV light, which exciteselectrons in the phosphors.

When the electrons in the phosphors returnto ground state, they give off red, blue, orgreen light, depending on the phosphor. Col-ored light from the phosphorescent cells ismixed to produce a full range of colors. LikeLCD displays, a pixel on a plasma display iscapable of producing white light when allthree subpixels—red, blue, and green—areactivated. Shades of color are produced byvarying the current flow to the subpixels.Plasma displays produce a bright image thatlooks good from all angles.

NEC PLASMA SCREEN

white light

liquid crystals

color filter

Red light is transmittedto the screen.

polarizing filmprismatic films

The voltage is off at this red subpixel. In this case, polarized light follows the twist of crystals, rotating90 degrees to pass the red color filter and on through the second polarizer.

APlasma displays

polarizing film


light into a smaller viewing cone to furtherincrease the brightness of the display.

The refracted light enters a polarizer thatcontains long inorganic polyiodide ions linedup lengthwise. Light that is oriented at rightangles to the iodine molecules passesthrough, while light oriented in the direction ofthe axis of the molecules is absorbed, cuttingthe brightness of the screen display in half.New light-enhancing films reflect light back tothe backlight panel that would have beenabsorbed by the polarizer. This reflected lightis then rescattered back toward the polarizer.These enhancement films, in combination withprismatic films, increase the brightness of atypical LCD screen by more than a factor of 2,reclaiming light that would have been lost.This makes your laptop or cell phone displaymuch brighter and easier to see. The samebrightness-enhancing films are used in manyof the newest LCD TVs. You may want to per-form your own investigation by visiting your

local department or electronics store. Ifyou look closely, you will be able

to determine which TVs havebrightness-enhancing

films and which donot. Hint: look for

the “Vikuiti”label on the

TVs.

New technologyLCD displays are changing fast. One of

the newest types is called LCOS, whichstands for liquid crystal on silicon. Whatmakes LCOS unique is the very high resolu-tion that can be achieved. LCOS displays usereflected rather than transmitted light, whichpasses through the liquid crystals twice on

its way from the light source to the viewer. Atypical LCOS panel can produce an imagethat reproduces the quality of a plasmaHDTV. LCOS displays are so small that theydo not use subpixels and color filters. In onetype of LCOS, light is filtered through a spin-ning color-wheel. Liquid crystal switching iscoordinated with the spinning color wheel,which moves too fast to see. A more sophis-ticated LCOS uses a system of prisms to splitlight source into red, green, and blue compo-nents and then recombines them by anotherprism to create the composite likeness.

This is just the beginning. Scientists,engineers, and chemists around the worldare developing new ways to use liquid crystalmolecules. At a recent conference in Boston,a company demonstrated an 84-inch diago-nal LCD TV. Others envision displays thatmight be rolled up to the diameter of yourpencil. Others are working to engineer dis-plays that use no battery, but rather are pow-ered by the same microwave transmissionsthat transmit information to your cell phone.

You can expect future displays to beboth smaller and much larger. And they willbe brighter, sharper, and cheaper, thanks tochemistry.

Brightness-enhancing film: Note the prismatic effect.

Two-way viewing angle LCD. This new LCD from Sharp Corporation sends the light from the backlightto the right and the left, making it possible to show two different images at the same time. Reflectingthe LCD in a mirror shows that one user sees a TV show, while another sees an Internet homepage.One possible application is a car display that shows the driver a map, while the passenger watches amovie on DVD.

Lois Fruen teaches chemistry at the Breck School in Minneapolis, MN. Her most recent article“Cleopatra’s Perfume Factory and Day Spa” appeared in the October 2004 issue of ChemMatters.

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10 ChemMatters, OCTOBER 2005

he drinking bird is a mesmerizing littlescience toy that has fascinated youngand old for more than 50 years. It isalso known as the happy bird, thedippy bird, the happy dippy bird, andother variations on this same theme. Itlooks like a bird and will bob up and

down as it appears to drink out of a glass ofwater. As long as it can reach the water, it willbob up and down indefinitely. The drinkingbird consists of two elongated glass bulbs thatare connected by a straight glass tube extend-ing well into the interior of the bottom bulb.The only way any substance can pass betweenthe two bulbs is through this narrow glasstube. The top bulb is covered with a porousfeltlike material that also makes up the beak.On top of the head is a plastic top hat, which isonly for decoration. Taped to the bottomchamber are tail feathers, which help it tomaintain balance. The whole thing is sus-pended from plastic legs, with a horizontalpiece of metal that acts as a pivot, allowing itto bob up and down.

Inside, the drinking bird is a highlyvolatile liquid known as methylene chloride(CH2Cl2). Since methylene chloride is color-less, coloring must be added to enhance thevisual effect. This liquid is also highly volatile,meaning it evaporates rapidly due to weakintermolecular bonds in the liquid state. Itsboiling point is 39.7 °C (103.5 °F), and itsvapor pressure at room temperature is 46 kilo-pascals (compared to only 3 kPa for water).Methylene chloride is somewhat toxic, so if adrinking bird breaks, care must be exercised incleaning it up. Methylene chloride is com-monly used as an industrial cleaner,degreaser, and paint remover.

After the methylene chloride is added bythe manufacturer, most of the remaining air isthen vacuumed out. Because a near vacuumnow exists within the bird, the highly volatileliquid readily evaporates until the space abovethe liquid is saturated with vapor. At this point,a dynamic equilibrium is established within thebird between the liquid and the vapor above it.Once equilibrium is established, anytime amolecule evaporates, another molecule willcondense, resulting in an overall constantamount of vapor within the bird as long as thetemperature stays constant.

To activate the drinking bird, his head isdipped into a glass of water, and he is then setupright in such a position that when he tips hisbeak, he will be able to reach into the glass of

http://chemistry.org/education/chemmatters.html

TheAmazing

Drinking Bird!

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TBy Brian Rohrig

water. Once the head is wet, a strange thingimmediately begins to happen. Like magic, thefluid begins to rise upward into the head, untilhis head fills with liquid. The head thenbecomes top heavy as the center of gravity ofthe bird is raised. The bird then topples over,takes another drink. As the bird tips over, theliquid flows back to the bottom bulb, restoringthe low center of gravity. The bird resumes itsupright position, beginning the whole processall over again.

To understand what makes the fluid risewithin the bird, think about what happenswhenever your own head gets wet. As long asthe relative humidity is not 100%, the waterwill immediately begin to evaporate. And evap-oration always causes cooling, because it is anendothermic process. That’s why you sweatwhen you get hot; it’s not the sweating itselfthat cools you, but rather the evaporation ofthe sweat from your body. Any phase changethat requires bond breaking will be endother-mic, because energy is required to breakbonds. This energy is drawn from the sur-roundings, thereby causing the temperature ofthe surroundings to decrease.

Because water evaporates from thehead of the bird, the head imme-diately begins to cool. This is themost crucial point in understand-ing how the drinking bird works.If you could cool the headanother way, the drinking birdwould work just the same. Whenthe head begins to cool, some ofthe vapor within the head willcondense into tiny droplets of liq-uid. A similar process occurs atnight when water vapor con-denses out of the air as it cools,forming dew on the ground.Because some of the vapor con-denses within the top chamber ofthe bird, there is now less vapor pressure inthe top bulb. Less vapor means less pressure.But the vapor pressure within the bottom bulbhas not changed. Because the vapor pressurein the bottom bulb is now greater than thepressure in the top bulb, the liquid is forcedupward into the top chamber. (Don’t say theliquid is sucked up into the top chamber—sci-ence never sucks!) Once the bird tips over,vapor from the bottom travels to the top untilthe pressure in both spheres equalizes and thebird begins the process all over again.

To understand how this pressure differ-ential can cause the fluid within the bird to

rise, consider what happens when you use anordinary drinking straw. When you suck fluidup into the straw, you are creating a region ofreduced pressure within the straw. Becauseoutside air pressure isgreater, it pushesdownward onthe surface ofthe fluid, forc-ing it up thestraw.

Not only is the drinking bird educational,but it can also provide hours of entertainment.Many science museums feature displays ofdrinking birds. No science classroom would becomplete without one. The amazing drinkingbird has even appeared in a 1995 episode ofThe Simpsons, where Homer positions adrinking bird in front of his keyboard to helpmonitor the controls at the Springfield nuclearpower plant. The artist Daniel Reynolds spent asmall fortune and several years developing anart exhibit comprising a whole flock of giant 61/2 feet tall drinking birds, each weighing3,000 times more than an original drinking

bird. They had to be made with a special vac-uum attachment in order to work properly.

There are many variations on the drinkingbird. They come in a variety of styles and sizes.There is even a drinking giraffe! The very pop-ular, but falsely named “hand-boiler” is noth-

ing more than a drinking bird that isstripped down to the bare essentials. It

works either by cooling the top orwarming the bottom.

The next time you need aunique gift for the person who

has everything, consider adrinking bird. A quicksearch on the Internet willreveal a plethora ofsources. They especially

make great gifts forscience teachers!


Brian Rohrig is a chemistry teacher at Jonathan AlderHigh School in Plain City, OH. His article “There’sChemistry in Golf Balls!” also appears in this issue.

Additionalexperiments you canperform with thedrinking bird:

1. Place a gallon-size freezer bagover an operational drinking bird.He will almost immediately stopdrinking. Can you explain why?

2. Have a drinking bird “drink” hotwater and then ice-cold water.Which will make the bird drinkfaster?

3. Have the bird “drink” a liquid witha higher evaporation rate thanwater, such as rubbing alcohol.Does the drinking bird drinkfaster?

4. Instead of cooling the head,heat the body, either with yourhand or a heat lamp. Does thedrinking bird work?

5. If you have a spare drinking birdthat you don’t mind disfiguring,paint the top bulb silver and thebottom bulb black. Place in asunny windowsill and watch itbob up and down! No waterrequired.

Cool headRed

absorbant

material

Goofy

top hat

Bird’s

Drink of

Choice

H2O

Feet for

balance

Feathers

for style

region of

lower

pressure

region of

higher

pressure

highly

volatile

liquid


or today’s cat owners, cat litter is as much a necessity as cat food. Butbefore 1950, most cat boxes were filled with sand, dirt, or ashes insteadof the more convenient superabsorbent litters, to which cat lovers arenow accustomed.

Kitty litter got its start when a neighbor frustrated with her cat track-ing ashes throughout the house asked a budding entrepreneur namedEdward Lowe for some sand. Lowe, whose family owned an industrialabsorbents company, convinced her to try clay instead. So Lowe sent the

neighbor home with an absorbent clay called Fuller’s earth. She loved it and soon woulduse nothing else in her cat box.

Her enthusiasm spurred Lowe to try to sell the stuff, which he dubbed “Kitty Litter,” as acat box filler. But the local pet store owner was doubtful that anyone would pay money for theproduct when the alternatives were available for next to nothing. So Lowe began giving itaway for free. Soon, he had satisfied customers willing to pay good money for Kitty Litter. By1990, Edward Lowe Industries was the largest producer of cat box filler in the United States.

The secret to Lowe’s Kitty Litter is granulated Fuller’s earth. Fuller’s earth is actually acatchall term for a chemically diverse set of absorbent clay minerals capable of absorbingtheir weight in water. Fuller’s earth litters naturally provide some odor control by sequesteringurine. But if the soiled litter isn’t replaced and urine begins to collect at the bottom of the box,bacteria found in feces will convert the uric acid in cat urine into unpleasant-smelling ammo-nia. Fuller’s earth litters can alleviate some of the ammonia odor by trapping the positivelycharged ammonium ions that are formed when water in urine protonates the ammonia. Toimprove odor control, cat litter manufacturers use a number of additives, including bakingsoda to absorb smells, fragrances to mask unpleasant scents, and antibacterial agents to killodor-causing bacteria.

Kitty LitterChem

http://chemistry.org/education/chemmatters.html

By Amanda Yarnell

F

Traditional clay litters like Lowe’s originalKitty Litter still make up about 40% of the catlitter market. But like ashes, dirt, and sand, tra-ditional clay litters must be discarded andreplaced fairly often, making cat box cleaning afrequent chore. Unhappy with the inconve-nience of traditional litters, biochemist and catlover Thomas Nelson began investigating alter-native clay formulations in the early 1980s. Heobserved that a certain type of clay called ben-tonite clumped up in the presence of moisture,allowing waste to be isolated and scooped out,leaving behind clean litter. Today, roughly 60%of the cat litter sold in the United States is ofthe clumping variety, and most of it is madefrom bentonite clay.

Bentonite is largely composed of mont-morillonite, a clay mineral made up of stacks ofSiO4 sandwiched between two sheets of octa-hedrally coordinated aluminum, magnesium, oriron. Substitution of lower-valence ions forsome of the higher-valence ones in the octahe-

dral sheets createsa negative charge imbalance thattraps cations, most often sodiumor calcium, between the stackedsandwiches.

The absorption power of var-ious types of bentonite is deter-mined by which cation is presentand in what amount. Becausesodium ions have a larger hydra-tion sphere than calcium ions do,sodium bentonite can absorbmore moisture than its calciumcounterpart, explains clay scientistShobha Parekh of Wyo-Ben, abentonite mining companyin Billings, Mont.Sodium-rich ben-tonite is there-

fore the material of choicefor clumping cat litter,she says.

Like traditionalclay litters, bentonitelitters provide someinherent odor control,thanks to their ability tosequester urine and totrap any NH4

+ producedfrom urine degradation.Recently, “crystal” cat litters that

promise improved odor control haveentered the market. The silica gel used to

make these crystals is chemically similar to thatused in desiccants. The silica gel crystals insuch litters are dotted with tiny pores, allowingthe crystals to absorb cat urine, then slowlyallow the water to evaporate off.

Some cat lovers fear—unnecessarily, catlitter manufacturers say—that their cats mightharm themselves by ingesting superabsorbentclay litters if they lick their paws after doingtheir business in the box. In response, a num-ber of companies are marketing plant-derivedalternatives made of wood pulp, corn, wheat—even peanut shells and orange peels.

For example, Swheat Scoop lit-ter, marketed by Detroit Lakes,

MN-based Pet Care Sys-tems, relies on natural

wheat enzymes toneutralize litter boxodor, while wheatstarches trapmoisture andclump firmly foreasy scooping. In

addition to beingsafe to eat, Swheat

Scoop and other plant-derived alternative litters

are biodegradable and canbe used as mulch or even flushed

down the toilet. Swheat Scoop founder MikeHughes estimates that more than 160,000 tonsof nonbiodegradable cat litter end up in munici-pal solid-waste landfills each year.

Despite this vast array of choices—bothclumping and nonclumping litters made ofclay, silica, and plant-derived alternatives—most cat lovers still think that cleaning thelitter box stinks.


Adsorption and absorption—different phenomena with similarnames. Adsorption is the attachment of a molecule to thesurface of a solid. Charcoal is an excellent deodorizer becausevapor molecules readily adsorb on its surface, and clay soilscan adsorb some gas odorants. Absorption is the taking up of asubstance into the porous interior of a solid—like a spongeabsorbing water.

Absorption vs. Adsorption

Particle channels

Particle

Adsorption

Absorption

+

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AM

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GETTY IMAGES

What is a hydration sphere? When dissolved inwater, ions hydrate (are surrounded by watermolecules electrostatically attracted to them).For positively charged ions like NH4

+, attractionto the strong partial negative charge on oxygenhelps create an inner sphere. The orderedstructure of the inner sphere creates, throughhydrogen bonding, a region in which thesurrounding waters are also somewhat ordered;this is the outer sphere. The number of wateraround different ions varies.


Amanda Yarnell is a writer on the staff of Chemical and Engineering News at the American Chemical Society. This article was adapted from Yarnell, A., What’s thatStuff?, Chemical and Engineering News, April 26, 2004, p. 26.

Clay layers

Dry Kitty Litter Wet Kitty Litter

Swellingof clay

interlayerH2O

Na+

NH4+In dry cat litter, sodium ions are trapped between clay

layers, but the clay still has an overall negative charge.When a cat urinates on the litter, the clay soaks up water(and NH4

+), and it swells, softens, and clumps. Theprimary driving force for this adsorption is the hydrationof the Na+. Extensive hydrogen bonding to and betweenthe clay layers also helps to trap odor (ammonia smell)and wetness.

These are atomistic models of sodiummontmorillonite before water adsorption and afterwater adsorption (O in red, H in gray, Na in blue, N ingreen, Si and Al in yellow, octahedral cations inpurple and green).

MODEL CREDIT: E. J. M. HENSEN (EINDHOVEN UNIVERSITY OF TECHNOLOGY) AND T. J. TAMBACH (UNIVERSITY OF AMSTERDAM).

Kitty Litter—The Molecular Vision

THERE’SCHEMISTRYIN GOLF BALLS!


There are only so many modifications youcan make to a tennis ball or a baseball, but golf balls areconstantly changing. Since Americans spend $650 mil-lion per year on golf balls, there is much finan-cial incentive for manufacturers to try to

find a ball that will go just a little farther andstraighter. Today, there are well over 90 differenttypes of golf balls available to the public! Onceyou hit the ball, the laws of physics govern whathappens to it. But the composition of the golfball itself is due to amazing advances in mate-rials science that are firmly rooted in chemistry.

Golf balls have come a long way sincethe first wooden ones were made in the 15thcentury on the east coast of Scotland. These

inefficient wooden balls were used until the mid-seventeenth century,when the “featherie” was introduced. The featherie was made from a

spherical leather pouch that was soaked in a solution of alum. Itwas then filled with “a top hat full” of wet goose feath-

ers that were softened by boiling. The feathersexpanded as they dried while the leather shrunk.

The result was a very hard ball. It was paintedwhite to make it more visible. At best, theseballs could travel from 150–175 yards,which was twice the distance that thewooden balls could travel. But the highprice of these first golf balls made thesport inaccessible to the common man. Asingle golf ball could be more expensive

than a club!

Morechemistry

is packed intoa golf ball thanany other piece

of athleticequipment.

Morechemistry

is packed intoa golf ball thanany other piece

of athleticequipment.

By Brian Rohrig

ChemHistory

DIMPLES AND SPIN—The physics of golf ball flight

Probably the most unique aspect of a golf ball is its dimpledsurface. A typical golf ball usually will have anywhere from300 to 500 dimples, with shallow dimples often alternating

with deeper dimples. Dimples may be of various shapes, from circu-lar to hexagonal to triangular. Dimples were officially introduced in1908 by the Spalding Company, but it was well-known for manyyears that a roughed up golf ball went farther.

How does it work? As the ball travels, it pushes the air out of theway, leaving a region of reduced air pressure behind the ball, knownas a turbulent wake. Think of a boat traveling through the water. Asthe boat pushes water aside, a wake is created behind the boat. Thesame thing happens as a golf ball travels through the air. Because thewake is essentially a region where air has been pushed away, there isa partial vacuum behind the ball. Air will rush in to fill this partial vac-uum. As a result of air rushing in to fill this partial vacuum behind theball, drag increases on the ball and the ball slows down.

However, with a dimpled ball, the tiny dimples on the surface ofthe ball create turbulence in the boundary layer—the thin layer of airsurrounding the ball. This turbulence is in the form of little vortices oreddy currents all along the dimpled surface of the ball. Air becomestrapped along the surface of the ball, causing air to flow farther downaround the ball before it separates to form the wake. Because less airis displaced, more air can flow directly around the ball, decreasing airresistance. The size of the wake behind the ball is greatly decreased.With a smaller wake, there is less drag and the ball travels farther.

If a golf ball is hit properly, it will spin as it moves through theair. The spin should be such that the top of the ball is moving toward

you (away from the direction the ball isgoing) and the bottom of the ball spin-ning away from you. This is known asbackspin and is imparted to the ball bythe grooves on the head of the club whenhit squarely. When a ball has backspin,the air that is moving over the top of theball is moving in the same direction asthe air that flows over the top of the ball,

causing the air along the top to move faster than the air underneaththe ball. According to Bernoulli’s principle, the faster the air moves,the less pressure it exerts. Because the air is moving faster over thetop surface of the ball, there is less pressure on the top and morepressure underneath. This increased pressure under the ball produceslift, keeping the ball in the air longer and allowing it to travel farther.Dimples help to produce lift because they increase airflow around theball, maximizing lift. End result—a dimpled golf ball will go twice asfar as a nondimpled golf ball.


In 1848, the gutta-percha golf ball wasintroduced. Gutta-percha is the dried rubber-like sap of the sapodilla tree from Malaysia.When this sap is heated to the temperature ofboiling water, it develops the consistency ofputty, allowing it to be fashioned into a solidball. When cooled, it becomes a very hardsphere. These balls could be inexpensivelyproduced. They could easily be reheated andreshaped if they became deformed. As a resultof these affordable balls, golf became increas-ingly popular. As these balls became nickedup from use, they traveled much farther.Eventually, these “guttie” balls were intention-ally made with rough surfaces, becoming theforerunner of today’s dimpled golf ball.

In 1898, a Cleveland, OH golfer namedCoburn Haskell produced a one-piece golf ballwith a rubber core that is considered the fore-runner of the modern golf ball. The solid rub-ber core was wrapped in rubber thread thatwas then enclosed within a gutta-perchapouch. These balls could be mass-produced,further lowering their cost. The Goodrich Com-pany came out with a pneumatic ball in 1906,

which had a compressed air core. Since gasesexpand when heated, these balls would some-times explode! Other manufacturers experi-mented with cores of metal, mercury, or cork.

In 1932, the United States Golf Associa-tion standardized the mass and size of all golfballs, which has remained constant up to thepresent day. The weight cannot be greater than45.93 grams (1.620 ounces) and the diametercannot be less than 42.67 mm (1.680 inches).Golf balls pretty much look the same now asthey did in the 1930s. But what goes on insidethe ball is another story.

The key to a good golf ball is its ability tobe both soft and elastic. Older golf ballsaccomplished this by having a hard elasticcore surrounded by a layer of rubber windingsthat looked like rubber bands. The elastic coreis the most important component. Elasticity isvery important, since the ability of the ball tospring back quickly is crucial to achievingmaximum distance. The elasticity of any sub-stance is measured by something called thecoefficient of restitution (CoR). The CoR issimply a measure of how bouncy a ball is. If a

ball is dropped from a height of 1 meter, andit bounces back 60 cm, then its coefficient ofrestitution is 0.6. If it bounced back 70 cm, itsCoR would be 0.7 at this particular velocity. Ifa ball were perfectly elastic, when dropped itwould bounce back to its original height. Anobject like a Superball has a coefficient ofrestitution that is close to 1. When dropped ona hard surface, it nearly bounces back to itsoriginal height. A piece of clay on the other

Ball with no spinBall with backspin

CESAR CAMINERO

What’s in your golf ball? Both of these moderngolf balls have an outer layer of Surlyn. If youlook closely at the bottom ball, you will see anadditional ring for the softer inner core. Themanufacturer claims this design reduces spinand helps the ball fly in a straight path.

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hand, has a CoR close to zero, since it doesnot bounce back at all.

The greater the CoR of a golf ball, the far-ther it will go when struck. A large CoR repre-sents a ball that is traveling very fast when itleaves the tee. A typical golf ball will have aCoR of approximately 0.8 when struck at 20mph and a CoR of around 0.6 when struck at100 mph. This does not mean that balls struckat 20 mph will go farther, but rather that lessenergy is lost at lower speeds than at higherspeeds. If the collision between ball and clubwas perfectly elastic, then 500-yard driveswould be the norm! Watch out, Tiger Woods!

Interestingly, it was the development ofthe Superball that led to many advances inthe golf ball. Superballs are made withpolybutadiene, a synthetic rubber with a verylarge CoR. However, by itself polybutadiene istoo soft to be used in golf balls. The key isthat the rubber must be vulcanized, whichmeans that the polymer strands must be par-tially cross-linked by a substance, which canadd to the double bonds in the polymer.Using vulcanized rubber, the CoR of golf ballscould be made even greater.

Elasticity is only one aspect of a golf ball,however. The golf ball must also deform sig-nificantly during the millisecond of contactbetween ball and club. This deformation is toobrief to witness with the naked eye but can bewitnessed using high-speed photography. Atthe moment of contact, the ball flattens con-siderably, losing as much as one-third of itsoriginal diameter. This deformation is only pos-sible because the bonds between moleculeswithin a golf ball act like tiny springs that canbe stretched and then snap back into place.

This flattening of the golf ball greatlyincreases the amount of time the club is incontact with the ball. If the club is in contactwith the ball for a larger period of time, youhave delivered a greater impulse to the ball. Agreater impulse means that more of themomentum of the club will be transferred tothe ball. That is why it is so important to fol-low through with your swing. In order to max-imize the time of impact between a golf balland club, the ball must deform when hit. Thegreater the time of impact between the cluband ball, the farther the ball will go.

One material by itself cannot give bothoptimal deformation and elasticity. Olderthree-piece golf balls met this challenge bybeing composed of a hard elastic core thatwould bounce back quickly. A hard elasticcore, however, does not deform very much

during impact with the club. That is why therewas a second layer of rubber windings aroundthe core. It was this middle layer thatdeformed during contact, while the core pro-vided the elasticity. This middle layer lookedlike little rubber bands. The ball would then becovered with balata, a nonelastic natural rub-ber obtained from the latex of South Americanrubber trees. These “rubber band” balls are nolonger manufactured today.

The more modern 2-piece golf balls arecomposed only of a large core and a thincover. If the core were made of only onematerial, it would be impossible to be bothsoft and elastic. Therefore, the core of the ballis made up of progressively softer layers, withthe harder layers on the inside. The two-pieceballs can then effectively mimic the 3-pieceballs in terms of both temporary deformationwhen struck and elasticity.

All golf balls today essentially have acore surrounded by either one or two layers.The core is always composed of some combi-nation of rubber compounds. Some lower-endballs also have a fluid-filled sphere at the cen-ter of the core. Today, nearly all golf balls arecovered with a synthetic outer layer, replacingthe natural balata covers. Higher-end balls aretypically covered with a synthetic rubber suchas urethane or a combination of rubber com-

pounds. Lower-end balls typically use Surlyn,which is a synthetic thermoplastic polymer.Thermoplastics soften upon heating.

The next time you go golfing (or watch iton TV), think of all the wonderful chemistrythat has gone into the humble little golf ball. Abig reason that records are continually beingbroken in golf, as well as many other sports,is because of improved technology. Under-standing a little about the science of golf willobviously not make you into the next TigerWoods, but it can’t hurt your golf game.


Brian Rohrig is a chemistry teacher at JonathanAlder High School in Plain City, OH. His article “TheAmazing Drinking Bird!” also appears in this issue.

Try this with a golf ball:1. Determine the density of a golf ball. Use the for-

mula D = M/V. Find the mass using a balance. To

find the volume, use water displacement, or use

the formula V = 4/3�r3. Because you probably

know what happens if you hit a golf ball into a

body of water, the density you arrive at should be

greater than that of water, which is 1 g/ml. You

can buy floating golf balls at a novelty shop.

These are made with a hollow core. If you can

find one, determine its density using the same

method.

2. Determine the coefficient of restitution of various

golf balls as well as other types of balls (like the

Superballs on page 4). Drop each from a height of

1 meter and measure the distance it rebounds. If

the ball rebounds 50 cm, its coefficient of restitu-

tion is 0.5 at that velocity.

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What is CBIRF?CBIRF stands for Chemical Biological

Incident Response Force. We’re part of theUnited States Marine Corps. If an individualis in trouble, they dial 911 and the policeand fire department come. But what hap-pens if those responders are overwhelmed?CBIRF assists the police and fire depart-ments in dealing with a horrific event, likethose resulting from bioterrorism orweapons of mass destruction.

I’ve worked as a research scientist forCBIRF for a little over a year. I’m actually acontractor for the military, but not a Marine.I’ve never served in the military a day of mylife! I’m the only individual in CBIRF thathas not. I just happened to come into thisfield. Most people in CBIRF are active-dutymilitary or retired military.

What is CBIRF’s job when a disaster strikes?Our mission is to save lives. The idea

is to go into a contaminated area andassess the area with equipment that detectschemical or biological contaminants. We’reasking ourselves: Which areas are cleanand which are contaminated? Once weknow the answer, we try to get people outof the contaminated areas safely andswiftly. That may sound simple enough, butthe scene could be disastrous. There couldbe people trapped beneath vehicles ortrapped in elevators or under desks.

CBIRF has an hour response time. Ifcalled, we get all the equipment rounded upand we leave the base in an hour. We havea second response force that’s ready to goin 4 hours if one group of responders isn’tenough.

CBIRF is located just south of Wash-ington, DC. Our main focus is protection ofthe Capitol. If a disaster happens elsewhere,then we have planes and boats that can getus where we need to be a lot faster thancars would.

Where does your work fit in with CBIRF’smission?

If there were a chemical or biologicaldisaster, the Marines can either take mewith them as an onsite chemist, or I canstay back in the lab to do some immediateresearch. I could use the Internet to look upinformation on the chemicals or biologicalhazards that are at the disaster site, howdangerous they are to people, and the signsand symptoms of exposure. If I have anidea what chemical or other hazardous sub-

Interview With a ChemistChristen Brownlee talkswith a chemist whose

mission is to save lives inthe event of a chemical,

biological, orradiological attack.

Erick SwartzResearch Scientist for CBIRF

PHOTO COURTESY OF ERICK SWARTZ


stance is at work, I can tell the Marineswhich piece of equipment they might use todetect it.

I also make sure pieces of scientificequipment we use to measure and detectchemicals are maintained and calibratedproperly. I train the Marines on how to usethe instrumentation that they take down tothe contaminated area, and I instruct themon the limitations and capabilities of thatgear. I like to satisfy my scientist side bytrying to figure out new ways to use theequipment more effectively.

Finally, I train the Marines how to han-dle hazardous situations. I help create sce-narios that deal with weapons of massdestruction in chemical, radiological, or bio-logical situations. The Marines’ instructionincludes some basic chemistry, a little bit oforganic and physical chemistry, and lots ofanalytical chemistry thrown in.

Have you responded to any disasters?Last year, there was a toxin called ricin

that was found in the Senate’s mailroom.There were potentially a thousand roomscontaminated with this agent, so we had tosend in a large force to clear the area. Ourresponders had to wear personal protectiveequipment (PPE), the white outfits that looklike space suits. Those can fully protect youfrom a chemical or biological agent.

I’m trained to respond to incidents inPPE, but during the ricin incident, I neededto stay back in the lab and do research onthe toxin. I had to instruct the Marines inhow to detect ricin and get it off their PPE,and I served as a resource just in casesomething else came up.

What are you doing the rest of the time,when there’s no disaster?

There’s no downtime because we’realways in training and preparing for thenext incident. Some weeks I’m dedicated toteaching the Marines general chemistry,and other times, we have equipment train-ing. It’s important to learn how to use ourequipment not only in the lab, but in a realdisaster situation, when you’re wearingPPE. It’s not as easy as it looks!

At least once a month, we actuallyhave disaster training for the Marineswhere they have to deal with casualties—other Marines who play out a disaster sce-nario. For example, our Marine actorsmight be coughing or wheezing like they

have symptoms of massive chlorine gasexposure. My job is to make it as realisticas possible. I feed the Marines all the infor-mation they would need to respond to thisdisaster situation, and they have to makedecisions on the fly.

What’s the best thing about your job? Howabout the worst?

I absolutely love my job here. The bestpart is that I’m helping to defend the coun-try in a lifeguard-like fashion so that whensomething bad does happen, I can helpdeal with it. The worst part of my job is thatI spend a significant amount of time fixinggear, which isn’t as exciting as doing realscientific research!

How did you get into this job? I was always interested in science as a

kid—I originally wanted to be a marinebiologist because I liked swimming andscience so much. But when I went to col-lege, I couldn’t get into a marine biologycourse. I took chemistry instead. Then I fellin love with all the instrumentation! Iended up studying atmospheric chemistryand getting a Ph.D. in physical chemistry.When I finished graduate school, I got apostdoctoral fellowship with the EPAstudying air pollution. Then September11th happened. I had about six weeksstudying the air around Ground Zero. Help-ing with the aftermath of that disastermade me a perfect fit for this job.

If you’re interested in chemistry now,

the best way to get a job you love is to con-tinue with your studies. Be curious, ask lotsof questions, and learn how to take testswell. In my field, you are tested a lot. Whenyou put on PPE and go into a hazardousenvironment, it’s the biggest test of all!Sometimes, the Marines will complain thatthe exams we administer are hard—butwhen you’re in a contaminated area, that[situation] will be difficult too. If somethingterrible does happen, we want to be on ourbest game.

Christen Brownlee is a freelance science writer inArlington, VA.

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Ricin is an extremelytoxic protein derivedfrom the castor bean(think castor oil). In anotorious 1978 inci-dent, Bulgarian oper-

atives used amodified umbrellacontaining a ricinpellet in its tip toinject dissidentGeorgi Markov.

Markov died threedays later from just

a 0.2-mg dose.

Erick Swartz and a marine are working on a portable gas chromatograph–mass spectrometer.

Factoid

The 37th InternationalChemistry Olympiad—Taipei, Taiwan59 countries gathered in July for a 10-daychemistry competition called the Interna-tional Chemistry Olympiad (IChO). Eachcountry sent a team of four top students.The competition included both a five-hourexam of basic knowledge and problemsolving and a five-hour laboratory practical.The level of difficulty of the challenge wason a par with mid-level college chemistrycourses. Medals were awarded based onthe total exam scores from both sectionswith the top students winning gold, silver,and bronze medals.

The results are in. The USA team wonthree silver medals and one bronze medal.South Korea won overall first place andAlexey Zeifman from Russian Federationwon the top gold medal.

Want to try out for the team next year?1. If you are a student who would like to

participate, check with your chemistryteacher.

2. If you are a teacher with students inter-ested in the United States NationalChemistry Olympiad (USNCO) program,contact your local section of the ACS. Ifyou are not sure whom to contact, findhelp on the Olympiad web page. Go towww.chemistry.org/education andselect the Olympiad link in the HighSchool section. Enrollment deadlines,contact information, and copies of pastexams are available at the site.

Celebrate NationalChemistry Week

National ChemistryWeek is October 16–22 thisyear. The theme is “The Joyof Toys”. The official web-site is athttp://chemistry.org/ncw.On the site you will find aneasy formula to make your own “bouncingball”. In addition, the American ChemicalSociety is sponsoring a poster contest forstudents in Kindergarten–12th grade. Stu-dents are invited to create a poster that willserve as a public service announcementemphasizing the role of science/chemistryin toys for their peers or other age group.

Renew or subscribeIt is possible that you received this issueas part of our National Chemistry Weekpromotion. If you have not renewed yoursubscription yet, it is not too late. Lastyear, we added multiyear subscriptions sothat you can lock in current rates for twoor three years.

Also, you can complete your class-room ChemMatters set with our new 20-year CD. You will find every issue from1983 through 2003 along with every Chem-Matters Teacher’s Guide ever published.We’ve made it easy to search for yourfavorite everyday chemistry topics featuredin ChemMatters over the years. The price isonly $25! Call 1-800-227-5558, or orderonline at http://chemistry.org/education/chemmatters.html.

Answer to quiz (page 4)Solution: A) Slinky B) Slip ‘n Slide C) Frisbee D)Hula Hoop E) Superball F) Hacky Sack

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Left to right: Scott Rabin (bronze), Allen Cheng(silver), Jacob Sanders (silver), NicholasSofroniew (silver).

Tell us what you thinkLet us know about the chemistry

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