A: To be sure, the wick does burn, butthe vast majority of light and heat given offrom a candle comes from the combustionof the wax, so I’d have to rule in favor ofyour teacher on this one. To be completelyaccurate, it’s actually the wax vapors thatare burning. Here’s how it works:

When you light the wick of a candle,the heat and light radiate out in all direc-tions: some of the heat radiates down andmelts a small portion of the wax around thebase of the wick. The wax used in candlesis not a single compound, but a mixture oflong, straight-chain hydrocarbon com-pounds—generally in the range of C20H42,C21H44, etc. Once the wax is melted, thesemolecules are free to move about, andbeing attracted to the molecules of stringthat make up the wick, they tend to soak upthe wick by a process known as capillaryaction. This is the same way that water isabsorbed by a paper towel. As the waxsoaks up the wick, the heat from the flamecauses it to vaporize; this allows the wax tomix with the oxygen in the air and burn.

“Burn” in chemistry meansto react exothermically

with oxygen.

The flame actually serves many pur-poses: First, it melts the wax of the candle,so that it can be “wicked up” the wick, andthen it vaporizes that wax so that it can mixthoroughly with the oxygen. Also, the flamecreates convection currents around it,which bring fresh air into the mix so thatthe wax can continue to burn. Also, theflame provides the activation energy for thereaction to take place.

Thus, the flame is a self-sustainingprocess: the energy released by eachhydrocarbon molecule as it reacts withoxygen enables the next molecule to bebrought up and burned. This continuesuntil either the wax runs out, the wick runsout, the oxygen runs out, or the cycle isinterrupted by a quick burst of air and aresounding chorus of “Happy Birthday toYou!”

If it’s true that the wax is the maincomponent that is burning, then you maywonder whether or not it is possible tolight a candle without the wick. To answerthis question, we need to define the term“flash point”. Flash point is the mini-mum temperature at which the vaporsabove a combustible substance can be litby an ignition source, such as an openflame. A lit match brought to a beaker filledof liquid pentane would immediately lightthe liquid on fire. But that same lit matchbrought to a beaker of wax would not catchit on fire—at least not at normalroom temperature. This is oddwhen you consider that both ofthese substances are made up ofthe same elements (carbon andhydrogen), and both are capableof burning. The difference lies inthe flash points: The flash point of pentane(–46 °C) is well below room temperature(25 °C), but the flash point of wax (205 °C)is well above it. This is mostly a result ofthe vapor pressure of these substances.Pentane’s very small-chain hydrocarbonmolecules result in much weaker intermol-ecular attractions; thus, pentane vaporizesreadily at room temperature, readilyenough to sustain a flame at its surface.

Below a certain temperature (–46 °C),pentane’s vapor pressure becomes lowenough that it would not catch fire. Wax,on the other hand, is made up of muchlonger-chain hydrocarbon molecules, andthus, it has considerably stronger intermol-ecular forces, strong enough to make it asolid at room temperature. This gives waxa very low vapor pressure, way too low tosustain a flame at its surface.

Above its flash point (205 °C), how-ever, the wax molecules will evaporate asufficient extent to sustain a flame, and itwould be possible to burn a wax candlewithout the aid of a wick.

2 ChemMatters, FEBRUARY 2005

By Bob Becker

Question From the Classroom

Q: Our chemistry teacher told us that when a candle burns, it’s really thewax that’s burning. I always thought that it was the wick that burns and thatthe wax is just there to make it burn slowly. Who’s right?

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

Intense heatat the top of the wick

causes paraffin tovaporize and then ignite.

Melted paraffinpuddled at thebase of the wickis drawn up bycapillary action.

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Vol. 23, No. 1 FEBRUARY 2005

COVER ILLUSTRATION BY STEVE DININNO CMTEACHERS! FIND YOUR COMPLETE

TEACHER’S GUIDE FOR THIS ISSUE ATwww.chemistry.org/education/chemmatters.html.

ChemMatters, FEBRUARY 2005 3

Production TeamKevin McCue, EditorCornithia Harris, Art DirectorLeona Kanaskie, Copy Editor

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

Technical ReviewSeth Brown, University of Notre DameFrank Cardulla, Northbrook, IL

Teacher’s GuideFrank Cardulla, 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, CTClaudia Vanderborght, Swanton, VTTerri Taylor, Silver Spring, MD

Frank Purcell, Classroom Reviewer

ChemMatters (ISSN 0736–4687) is published four times ayear (Oct., Dec., Feb., and Apr.) by the American ChemicalSociety at 1155 16th St., NW, Washington, DC 20036–4800.Periodicals postage paid at Washington, DC, and additionalmailing offices. POSTMASTER: Send address changes toChemMatters Magazine, ACS Office of Society Services,1155 16th Street, NW, Washington, DC 20036.

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Question From the Classroom 2How does a candle work?

ChemHistoryThe Great Hartford Circus Fire 4Use of a flammable waterproofing agent on a circus

tent led to a terrible tragedy in 1944.

ChemSumerMore Than Blue 8Chemical imbalances in the brain can be involved indepression. How do chemicals like Prozac rebalancethat brain chemistry and bring relief for millions of peoplesuffering from the disease?

The Silent Killer 12A car left idling in a garage. An improperly working furnace.Both are sources thatproduce carbon monoxidegas, which can kill orinjure without warning. Whyis this gas so deadly? Howcan it be detected?

Water of Life 16Planet-wide, the solvent of choice for living

things—plants and animals alike—is water, and we all rely on it for nutrition, transport, reproduction,you name it. What’s to know about H2O?

ChemShorts 19Measuring oxygen content of the blood in real

time and ice spikes that you can make in your freezer.

Chem.matters.links 20

on theweb

on theweb

on theweb

on theweb

ChemHistory

It was a hot summer day in thesouthern end of Hartford, andthe Ringling Brothers and Bar-

num & Bailey Circus was in townfor two shows, which were to beheld under the big top.

The show began eight minuteslate at 2:23 pm on that fateful day.Minutes later, a flame leapt up froma side wall and quickly began toburn the tent.

The fire started out small, butas it gained oxygen and fuel, it grewto the point where it could be seenclearly by the audience. At first,

many thought it was just part of theshow and did not realize that itposed a life-and-death situationuntil it hit the roof and began tospread rapidly.

People began to panic and rushfor the exits. Because the walkwaysaround the tent were narrow, theybecame crowded and chaotic. Ani-mal chutes also blocked many exits,and once people realized this, theyhad to turn around back into thebedlam. Within minutes the wholeroof was engulfed in fire and themain support poles began to give

By Brendan Rimetz

Fire has the ability to mystify and amaze us andalso scare and horrify us.It can heat our homes andcook our food, but it can

also kill us. It is uncontrol-lable and unforgiving when

not properly controlled,and it can spread with

overwhelming speed whenconditions are favorable.

An unforgettable display ofthe power of fire took

place in my hometown ofHartford, CT, on

July 6, 1944.

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

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way and collapse on thepeople below. The meltedburning pieces of canvasfell and stuck to people’sskin.

Eventually, the tentcollapsed on all of thoseinside. The incredible heatof the fire cremated manyof those who were killed.Although many people didsurvive, and there weremany amazing rescue sto-ries, 167 died in total, andover 700 were injured.

How could somethinglike this have happened!?

Gasolineand paraffin

Much of the blame forthe rapid spread of the fireand intense heat restssquarely on the choice ofwaterproofing agent for thetent. Because World War IIwas still raging and theU.S. military needed asmany supplies as theycould get, the circus own-ers weren’t granted the useof the safe waterproofingagent they had wanted.The owners would later claim that becausethere was no other safe, effective means of waterproofing a largecanvas, the circus owners had to rely on a mixture of paraffin waxand gasoline to waterproof their tent. Although this mixture hadworked well before, it was very flammable and had caught fire manytimes before the Hartford fire. But if the ownerswere to hold shows in the rain, to maximize theirprofits, they had to rely on this flammable mix-ture.

WaterproofingTo understand waterproofing, you need

to understand water. As you know, watermolecules are composed of two atoms ofhydrogen and one atom of oxygen.Because of the different characteristics ofthe oxygen and hydrogen atoms, thearea of the water molecule near theoxygen atom is slightly negativelycharged, and the area near the hydrogenatoms is slightly positively charged. Molecules that have

this type of charge separa-tion are called polar mole-cules. Water's polar naturecauses its molecules tobond to each other betweentheir positive and negativeends.

Substances such asgasoline and paraffin waxare hydrocarbons, consist-ing only of carbon andhydrogen. Because carbonand hydrogen have verysimilar electronegativities,carbon-hydrogen bondsare nonpolar, and thehydrocarbon molecules donot have positively or neg-atively charged ends.Water molecules wouldrather adhere to them-selves than to a nonpolarwax surface. This is whywater beads up on a water-proofed tent. Paraffin is agreat waterproofing agenton its own, but it is nor-mally a solid. Gasoline isused to dissolve paraffin,so that the pasty mixturecan be “painted” or spreadon the tent.

A bad combination

Because the whole top of the tent was covered in the gasolineand paraffin mixture, it provided a large amount of fuel; up to 800pounds of paraffin wax and 6000 gallons of gasoline by someaccounts.

The two substances are combustible, but their propertiesvary. Although paraffin is combustible, it needs

to be heated to burn. Paraffin waxis the slow-burning fuel that keeps

candles burning for hours. But youcan drop a cigarette or match next to

paraffin and not have it ignite.Gasoline, on the other hand, is

very flammable, which means it has alow flash point and is easily ignited. The

flash point is the lowest temperature atwhich a liquid can form an ignitable mix-

ture in air near the surface of the liquid.The lower the flash point, the easier it is to

A survivor’s storyMy grandmother, 12-year-old Alice Linde was at the circuson the day of the fire. “I went to the fire with my dad, myyounger brother, and sisters”, she recalls. “We sat up highin the bleachers next to the circus band. While the lion actwas just getting over, I looked up over at the reservedseating section of the tent and saw the ceiling on fire. Iturned to my dad and yelled “Fire!”, and that is wheneveryone around us looked up and started to panic. Mydad sat us calmly in the seats as he looked around. Next,he gave us instructions to exit underneath the bleachers.He dropped us one by one behind the bleachers and toldus to head for the nearest exit. I was to hold my 4-year-old

sister’s hand as we ran toward the exit whichhappened to be down the hallway of the circusentertainers’ dressing rooms. Once outside thedoor, I turned and realized that it was someoneelse’s hand I was holding and not my sister’s.She escaped safely with someone else. Allaround us were the circus entertainers, someactually naked because they ran out so quickly.My dad quickly found us, and we stood outsideto watch. Being only 12 at the time, it was a sadand unforgettable sight to see all the entertain-ers around crying and frenzied,” said Alice, who

ChemMatters, FEBRUARY 2005 5

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ignite the material. Gasoline has a flash point of –40 ºC and is moreflammable than paraffin wax which has a flash point of 204–271 ºC.

Gasoline provided the flammable vapor that started the fireand heated the paraffin, which, in turn, ignited and kept the tentburning.

Problems fighting the fireThe reaction that took place in this event is classified as a

combustion reaction. In a combustion reaction, a compound orelement, in this case, gasoline and paraffin, reacts with oxygen torelease energy rapidly in the form of heat and light, hence, the fire.

Because the tent was outside and there was plenty of availableoxygen, the fire spread quickly.

As mentioned before, gasoline and paraffin are both nonpolarand mix together well, but they don’t mix well with polar water.This caused a great setback for those who tried to put the fire outusing the fire hoses and dousing the flames with buckets of water.The flaming mixture of paraffin and gasoline simply floated on thewater and continued to burn. In fact, the flowing water actuallyspread the fire around and worsened the situation.

The fire needed to be smothered or cooled, but water could doneither, and modern equipment and fire-fighting foams (see Chem-

Matters, April, 2001) were notavailable at that time. This made itvirtually impossible for the firefight-ers to extinguish the fire.

AftermathImmediately after the disaster,

Ringling Brothers and Barnum &Bailey Circus announced that itwould not use the big top tentsuntil they could be rebuilt and fire-proofed. By the time of this

announcement, theyhad already purchaseda waterproofing agentthat was also fire-proof. Hooper FireChief fireproofing waspurchased by the cir-cus and used to fire-

proof the side walls of the dressingrooms and sideshow tents. Thesubstance was a thick, milky sub-stance that had been successfullyused by the U.S. military to fire-proof truck and boat covers. It wasadvertised as waterproof and resis-tant to mildew. The advertisementspointed out that “…for nearly aminute a blowtorch was applied toa section of the chemically treatedsideshow tent. As the first flamestouched the canvas, it began toglow a bright red … . When theflame was removed the glow diedout, leaving a blackened charred-edge hole in the fabric.’”

It still would be a long timeuntil Ringling Brothers and Barnum& Bailey Circus would overcomethe bad publicity from the fire.After the fire they were sued and

The paraffin and gasoline mixture used towaterproof the tent shares some simi-larities with a notorious substance. Everheard of napalm? It’s best known for its

use in bombsduring the fire-bombing ofTokyo, Japan,and Dresden,Germany, dur-ing World WarII, as well asits use during the Vietnam War. The military discovered that traditionalbombs, and bombs with just gasoline, explode and burn too quickly tobe effective at starting fires on the ground. Napalm was a jellied gasolineformulation originally made from gasoline, naphthalene, and palmitate. Itwas sticky, highly flammable, but also slow burning. Sound like anywaterproofing agent you’ve just read about?

Similar tonapalm, whena small amountof the tentwaterproofingagent isignited; itrapidly dripsand spreads asustained firedown a stick.

The waterproofingagent used on thecircus tent was adangerouscombination ofgasoline andparaffin. When aquarter-sizeddollop ignites, itmelts andspreads rapidly.

A s h o c k i n gs i m i l a r i t y

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ChemMatters, FEBRUARY 2005 7

ended up paying 10 years’ worth of profits to fulfill claims by thevictims’ families. The company never fully recovered from the fireand its repercussions. Shortly after the fire, it stopped using bigtops and tents for the circus shows. Instead, the circus companydecided to perform in arenas and stadiums. In 2000, the RinglingBrothers and Barnum & Bailey circus was preparing to tour the

United States under atent for the first timein more than 40years. Since the fire,Connecticut andmany other stateshave passed fire pre-vention laws thatstrictly regulate theway circus tents areconstructed.

Many questionsremain about how thefire started. To thisday, no one is reallyquite sure about howor where the fire

started. Many blame a carelesslytossed match or cigarette. Still others,

think it was arson. In 1950, a mentally unstableman named Robert D. Segee claimed he

started the fire, but Connecticut investiga-tors were never able to prove that he was

in the state that day, and he laterrecanted. We may never know who orwhat started this disaster.

The fire is still a very painful mem-ory in Hartford. Almost all of the 167victims of the fire were eventually identi-

fied, yet six remain unidentified to thisday.

After 60 years, a monument at the siteof the fire will finally be erected for the vic-

tims. On July 6, 2004, I joined with my highschool chemistry teacher, Ms. Coan, survivors, and

the citizens of Hartford to remember The Great Hartford

Colloidal dispersions—Oil and water mix!?

Instead of dissolving paraffin or some other oil-based waterproofing agent in gasoline, why notdissolve it in water instead? Water is cheap and,most importantly, nonflammable. But is this possi-

ble? You’ve probably already heard that “like dissolveslike” or the more common “oil and water don’tmix.” Sometimes, this helpful rule isn’texactly true.

In the presence of soap solution,oil from your clothing can be drawninto water to form a colloid. A col-loid essentially consists of parti-cles of one substance dispersedthroughout another. Soap mole-cules are able to form sphericalstructures in water, known asmicelles, with hydrophobic(water-fearing) tail interiors andhydrophilic (water-loving) headexteriors. A soap micelle, with an oildroplet in its center, can remain sus-pended in water indefinitely.

The difference between asolution and a colloid is some-what arbitrary. In a solution, thedifferent ingredients dissolveinto tiny particles less than 1 nanometer (nm) in diameter. In a typical stable colloid, theparticles are larger, up to 100 nm, although they are stillinvisible without an optical microscope.

Milk is a familiar liquid-in-liquid dispersion (emul-sion) of protein and fat in water. In fact, before commer-cial paint was available, people used to paint theirhouses with homemade formulations of milk, lime(CaCO3), and available pigments. Depending on the num-ber of coats given to bare wood, milk paint can be a verywater-resistant coating.

The exact ingredients of Hooper Fire Chief Fire-proofing are unknown today, but the description of it asa thick milky substance suggests that it was similar towater-based paint, which is a solid-in-liquid colloid.

A soap micelle, with an oildroplet in the center, canremain suspended in waterindefinitely. Without soap,the droplet would merge withothers of its kind, making alarge pool of insoluble oil.

Brendan Rimetz is a high school junior at East Catholic High School inManchester, CT. He enjoys writing about chemistry and sports. He would liketo thank his chemistry teacher, Mrs. Amy Coan, for all of her assistance.

FURTHER READING O’Nan, Stewart. The Circus Fire. First Anchor Books: New York, 2000.

Mayor Perez ofHartford at thededication ofthe memorial.

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ChemMatters, FEBRUARY 2005 19

Ice spikes

T alk about your strange, yetordinary things—ice spikes

are real oddities. It’s even possi-ble you’ve seen them in a freezernear you! They grow out of icecube trays,formingcurious-lookingpeaks up to5 cm high.

Underthe rightconditions,ice spikesgrow aswaterfreezes in an ice cube tray. Put atray in the freezer, and you willnotice that freezing begins at theedges of the tray. As surfacefreezing moves in from theedges, a small hole can beleft at the top of eachcube. At the sametime, the bottom andsides of the cubeare also freezing. Asyou know, whenwater freezes, itexpands andbecomes lessdense. The pressurefrom the expandingice forces the remain-ing unfrozen water up

through the hole. It eventuallyforms a spike.

You’ve never seen them?The reason could be related tothe purity of your water. Accord-ing to research mentioned on theWeb site SnowCrystals.com, the

presence of even small amountsof NaCl can reduce spike pro-duction.

So how do you makeyour own ice spikes? Buy

some distilled waterand fill up your ice

trays. If you can’tmake ice spikesafter a few tries,consider raisingthe temperatureof your freezerto just belowfreezing. Your

freezer might betoo cold to allow

the formation ofspikes.

Pulse oximetry

I f you’ve visited someone atthe hospital recently, you

might have seen a clip attachedto their finger with a red lightcoming out of it. The clip is actu-ally a probe attached to a moni-tor that gives pulse rate, as wellas the percentage of oxygenationof the blood—important infor-mation for a doctor to knowfrom moment to moment.This noninvasivemethod is known aspulse oximetry.

How doesit work? Theprobe shinestwo wave-lengths (650and 805 nm)of lightthrough thefinger, earlobe,or foot of thepatient and detectshow much of the lightis absorbed. Hemoglobin—the oxygen-carrying protein inblood (see “The Silent Killer” inthis issue)—absorbs light at dif-ferent wavelengths depending onwhether oxygen is attached to it.Measuring the absorption oflight at two wavelengthsenables a computer proces-sor to quickly calculate the per-

centage of hemoglobin saturatedwith oxygen. If oxygen satura-tion falls below a predeterminedlevel, say 90%, an alarm bellsounds to alert medical staff.

ChemShorts

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The red glow comes from aprobe attached to a baby’sfoot. Pulse oximetry allowsdoctors to continuouslymonitor percent bloodoxygenation.

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1155 Sixteenth Street, NWWashington, DC 20036-4800

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Chem.matters.links

The 37thInternationalChemistryOlympiad—Tapei, Taiwan

Do you have what it takes tobe a chemistry Olympian?

Each year, over 200 of the besthigh school chemistry students,their mentors, scientificobservers, andguests frommore than 60countries gatherin July for a 10-day chem-istry competitioncalled theInternationalChemistryOlympiad (IChO).

The competi-tion includesboth a five-hourexam of basicknowledge andproblem solving and a five-hourlaboratory practical. The level ofdifficulty of the challenge is on apar with mid-level college chem-istry courses. Medals are award-ed based on of the total exam

scores from both sections withthe top students winning gold,silver, and bronze medals.

The U.S. team has performedwell at the international event. In1999, the team placed first andwon the top gold medal; in 2000,a member of the U.S. team wonthe top individual gold medal.

How will the top U.S. stu-dents be selected in 2005? As

the result of aselection processthat may includeexaminations,science fairs, orteacher’s recom-mendations, 800students repre-senting 125 ofthe local sectionsof the AmericanChemical Society(ACS) will bechosen to takethe U.S. NationalChemistry

Olympiad examination in March.On the basis of their perfor-

mances on the qualifying exam,twenty of the nation’s top highschool chemistry students will beselected to attend a 10-day study

camp to be held in June at theU.S. Air Force Academy inColorado Springs, CO.

At the camp, students willtake part in an intensive studyprogram that includes organic,inorganic, analytical, and physi-cal chemistry. During the twoweeks, the camp directors willobserve student performancesrelated to laboratory work, team-work, and basic knowledge. Atthe end of the camp, fourfinalists and two alternateswill be selected to repre-sent the United States atthe 37th InternationalChemistry Olympiad inTaipei.

Want to try outfor the team?1. If you are a student

who would like to participate,check with your chemistryteacher.

2. If you are a teacher with stu-dents interested in the U.S.National Chemistry Olympiad(USNCO) program, contactyour local section of the ACS.If you are not sure whom tocontact, find help on theOlympiad Web page. Go to

www.chemistry.org/educationand select the Olympiad linkin the High School section.Enrollment deadlines, contactinformation, and copies ofpast exams are available atthe site.

The ChemMatters20-year CD

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new 20-year CD. You’ll find everyissue from 1983 through

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