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FEBRUARY 2002 Pseudoscience No matter how good it sounds, it just isn’t true.

Maple Syrup It’s smooth, sweet, and supersaturated. Mighty Thermite Here’s a solid reaction that’s sure to be a hit. Question From the Classroom By Bob Becker

Q. I was surfing the Web and found that there is a new hydrogen beer. Is it true?

A. According to numerous • The bottles are packed in fact from accounts on the Internet and special crates lined with con- fiction? beyond, the Tokyo-based crete to prevent chain explo- It’s not Asaka Beer Corporation has sions in the event of a fire. always easy, taken a “bold new step that And the MOST amazing but in the case may revolutionize beer “fact” of all: of hydrogen production throughout the • Hydrogen beer has beer, it should world.” Seems they have inspired a daring and dazzling have been. succeeded in manufacturing a new fad of belching match- To begin with, beer in which some of the ignited blue flames from one’s very few gases are dissolved carbon dioxide is mouth. as soluble as carbon replaced with the much Does all of this sound too dioxide in water. Those lighter, fizzier hydrogen gas. incredible to be true? That’s that are— Of course, the articles because IT IS! ammonia (NH3) and hydrogen point out, this newfangled car- Hydrogen beer ranks right chloride (HCl), for example— certainly end up with an ignit- bonation (or better, “hydro- up there with an ever-growing wouldn’t make acceptable ed mouth! genation”) was intended as a number of urban legends. The beverages! Hydrogen gas Finally, the biology is all more environmentally friendly only truth in the previous (H2) has one of the lowest sol- wrong. We belch from our alternative to carbon dioxide, a paragraphs is the existence of ubilities of any gas in water. It stomachs through the esopha- well-documented greenhouse dozens of Web sites, each would take a heroic amount of gus, but we talk and sing gas. And the fact that hydro- describing the remarkable applied pressure to get using air expelled from our gen gas is also tasteless is properties of hydrogen beer, enough hydrogen to dissolve lungs. The human airway, or said to preserve the “natural but each leaving out one small in a bottle of beer to supply trachea, comes capped with flavor” of the beer. but critical detail—it doesn’t the necessary fizz—far more an epiglottis, a thin cartilage It’s a huge seller! exist! than ordinary bottles or cans flap designed to keep food and Apparently, in karaoke clubs, If you fell for this could withstand. And even if air going in the right direc- customers are now quite hoax, you are not alone. the can could hold that much tions when you swallow. skilled at timing their belches A reputable physics pressure, popping the top of If you found the hydrogen to help them hit the high Web site, several news- such a container would be a beer story hard to swallow, notes. As these articles papers, and even a life-threatening act! congratulations! And don’t explain, “hydrogen, like heli- chemistry textbook refer And then there’s that blue forget to give your chemistry um, resonates at a higher fre- to the amazing product. flame detail! In fact, a hydro- teacher some extra credit quency in the voice box Although we know gen flame is nearly colorless, while you’re at it! Not all hoax- resulting in a much high- better than to believe making it just about invisible es are so easy to debunk, er pitch when talking or everything we read, even in a dark room. The however. A few helpful Web singing.” many of us still fall chemistry just isn’t there. sites are dedicated to sorting There are other for online hoaxes. Neither is the physics. out Web-based fact from fic- amazing “facts” avail- The fact is that any- Hydrogen is a low-density tion. Here are a couple of able on Web pages: one can post an e- gas. Once released, it rises far dependable and entertaining • The bottle caps mail hoax, sometimes too quickly to launch those guides. are equipped with safe- even setting up offi- horizontal fireballs! Even http://urbanlegends.com ty valves to prevent cial-looking Web scarier, hydrogen molecules www.snopes2.com excess buildup of pages as links to “sub- move so quickly that any per- pressure at high tem- stantiate” the story. son attempting to light a Now, about that new fish beer. peratures. How do we separate hydrogen belch would almost

2ChemMatters, FEBRUARY 2002 ¨

Vol. 20, No. 1 FEBRUARY 2002 DEPARTMENTS Question From the Classroom 2 I was surfing the Web and found that there is a new hydrogen beer. Is it true? Do you believe everything you read on the Web? You can thank your chemistry teacher if you saw right through this one. Activity 10 How Dense Is It? PHOTO BY MIKE CIESIELSKI Both aquarium owners and syrup manufacturers use a handy measuring device called a hydrometer to compare the densities FEATURES of solutions. You can make, calibrate, and test your own. Pseudoscience—Too Good To Be True? 4 ChemSumer 11 Whether it’s the Loch Ness monster or the Bermuda Triangle, these fantastic tales are fun to think about. But what happens The Fizz-Keeper: Does It Really Keep the Fizz? when we apply the science? You’ve seen them in supermarket beverage sections. Pump up the pressure and save the fizz. Does the Fizz-Keeper work? Aquarium Chemistry—Life in the Balance 6 Try it for yourself. From the smallest fishbowl to the biggest public aquarium display, keeping fish healthy takes patience, careful monitoring, Chem.matters.links 16 and a good knowledge of chemistry. Are you gullible or skeptical? Take this quiz to decide. Maple Syrup: Sweet Sap Boils Down to This 8 Steaming pancakes with hot maple syrup—what better way to start a February morning? In New England, the sap is flowing and sugaring is underway. Mighty Thermite—A Solid Hit! 14 Can two solids react? You’d better believe it! Iron and alu- minum get together for an exothermic display called thermite. TEACHERS! FIND YOUR COMPLETE uzzler TEACHER’S GUIDE FOR THIS ISSUE AT CM P www.chemistry.org/education/chemmatters.html. Why is it easier to swim in salt water than in fresh water? Find the answer in this issue of ChemMatters!

COVER PHOTO BY MIKE CIESIELSKI

Production Team Division of Education and paid at Washington, DC, and addi- by contributors. Views expressed Helen Herlocker, Managing Editor International Activities tional mailing offices. POSTMAS- are those of the authors and do not Cornithia Harris, Art Director Sylvia Ware, Director TER: Send address changes to necessarily represent the official Leona Kanaskie, CMCopy Editor Janet Boese, Assistant Director for ChemMatters Magazine, ACS Office position of the American Chemical Society. Administrative Team Academic Programs of Society Services, 1155 16th St., Michael Tinnesand, Editor Policy Board NW, Washington, DC 20036. Susan Cooper, Chair, LaBelle Julie Farrar, Creative Director All rights reserved. No part of this High School, LaBelle, FL Elizabeth Wood, Manager, publication may be reproduced, Lois Fruen, The Breck School, Subscriber Information Copy Editing Services stored in a retrieval system, or trans- Minneapolis, MN Prices to the U.S., Canada, and Guy Belleman, Staff Associate mitted in any form by any means, Al DeGennaro, Westminster High Mexico: $10.00 per subscription. Sandra Barlow, Program Assistant now known or later developed, © Copyright 2002, School, Westminster, MD Inquire about bulk, other foreign including but not limited to electronic, American Chemical Society Technical Review Team Doris Kimbrough, University of rates, and back issues at the ACS Seth Brown, University of Office of Society Services, 1155 mechanical, photocopying, record- Colorado-Denver Canadian GST Reg. No. 127571347 Notre Dame, IN 16th St., NW, Washington, DC ing, or otherwise, without prior per- ChemMatters (ISSN 0736Ð4687) is 20036-4800; 800-227-5558 or mission from the copyright owner. Frank Cardulla, Northbrook, IL Printed in the USA published four times a year (Oct., 202-872-6067 fax. Requests for permission should be Dec., Feb., and Apr.) by the directed in writing to ChemMatters, Teacher’s Guide American Chemical Society at 1155 American Chemical Society American Chemical Society, 1155 Frank Cardulla, Editor 16th St., NW, Washington, DC assumes no responsibility for the 16th St., NW, Washington, DC David Olney, Puzzle Contributor 20036-4800. Periodicals postage statements and opinions advanced 20036-4800; 202-833-7732 fax.

ChemMatters, FEBRUARY 2002 3 ILLUSTRATION BY BRUCE MACPHERSON

Little Red Riding Hood had a problem. She couldn’t tell her grandmother from a wolf. Did you have trouble with that story line when you were a child? After all, wolves don’t look anything like grandmothers, even wolves dressed up in wigs and By Frank Cardulla dresses. Any self-respecting storybook character should have known better. But then again, maybe the disguise was really a good one. Who knows? • The planetary positions on the day we were born influence the ways It’s just a story. our personalities and talents develop throughout our lives. • The Bermuda Triangle is a geographic area off the coast of North here are clever wolves in books as well, disguising themselves America where certain forces have been known to cause ships and as real scientists. And you’ll find them not just in books, but also planes to disappear. T in every imaginable media, print or otherwise. Some are such • Alien beings have visited Earth and abducted human beings. After obvious fakes that only the most near-sighted Little Red Riding Hood performing experiments on them, they have returned these individ- would be fooled. But others are so well disguised, that it’s hard— uals to Earth. almost impossible—to see the wolf behind the scientific facade. • Some people can move objects by mental force alone. How about you? Can you spot a wolf disguised as a scientific fact? If you picked out one or more “probably true” statements in the list, Consider the following statements. Pick out the ones you think are defi- you are not alone. But, in fact, not one of these statements is supported nitely or probably true. by mainstream science. • Some people can read other people’s minds. They are born with an A lot of us read our daily horoscope—little statements of how the ability to communicate by extrasensory means. planets and stars will impact our lives today. It’s fun. But do you believe • Some people have the psychic ability to predict the future. They in astrology? About 36% of the U.S. population believes that astrology is actually see events before they occur. either “very” or “sort of” scientific. How about extra sensory perception

4ChemMatters, FEBRUARY 2002 www.chemistry.org/education/chemmatters.html (ESP)—the mind-reading thing? About 50% of your teenage peers buy Can you prove it’s true or false? this one. “I was thinking about her and, just then, she walked into the Think about this example: Suppose I claim that as long as someone room!” Easily forgotten are the hundreds of times he was thinking about believes that grass is green, he will never die. Someone dies. “Obvi- her when she didn’t appear! We all do it! There’s even a name for it. It’s ously,” say I, “he stopped believing that grass is green!” Am I right? called selective thinking—remembering and selecting evidence that is Who can tell for sure? There’s just no way to prove that the claim is favorable toward your claim, and ignoring evidence that is unfavorable. I either true or false. can prove that a flipped penny will always land “heads” if you allow me Here’s another one. “There’s a large reptilian monster swimming in to ignore those times when it lands “tails”. Loch Ness in Scotland.” Am I right? Despite the lack of even one piece of verifiable evidence that the monster exists, how can we rule out that the Exceptional science is fun. evidence will surface next week? Again, beware the wolf! Scientists are also good at spotting something called the ad hoc But is it true? hypothesis. This is a hypothesis that’s created to explain away anything The list of fascinating, incredible scientific-sounding phenomena is that seems to contradict one’s claim. Suppose that you go to an so extensive that you could spend a lifetime sifting through the claims. astrologer for a personalized chart showing how the planets and stars Homeopathy, Atlantis, Dianetics, pyramid power, spoon bending, the will influence your life in the next month. But the actual results aren’t predictions of Nostradamus—how can you decide about them when they even close to reality! You lose the class election and fail to find true love sound so believable and they are so widely accepted? despite all the astrological signs in your favor. Don’t worry, the Perhaps Carl Sagan said it best. “Exceptional claims require excep- astrologer has a ready hypothesis that explains all. “There must have tional proof.” been other, stronger planetary influences that caused the variation!” Frankly, it’s fun to believe exceptional things. They’re interesting. Wolves always have ever-ready hypotheses for explaining away inconve- Besides making for good conversation, they make captivating stories, nient problems. movies, and television. Humans have believed in exceptional things Scientists are always skeptical about ad hoc hypotheses. When throughout recorded history—perhaps because for most of history, so German scientist Alfred Wegener first proposed the theory of continen- little was known about the laws that govern nature that one explanation tal drift—now fully accepted—he was greeted with skepticism. What may have seemed just as reasonable as any other. force would be strong enough to move entire continents? Wegener Being open to new ideas is a characteristic of intelligent, creative came up with an ad hoc hypothesis—gravity. He might have been better thinkers. But being “open-minded” does not mean taking ideas at face off saying that he didn’t know. Calculations showed that even if conti- value. Good thinkers pride themselves on being skeptics. They carefully nents could be moved by gravity, they would soon crumble as they examine every new idea in the light of basic scientific laws and well-estab- moved through rocky ocean bottoms. As a result, scientists, wary of a lished theories. And they can usually tell their grandmothers from wolves. wolf, rejected the theory. After Wegener’s death in 1930, Arthur Holmes And by using science—REAL science—it’s likely that you can too. found that convection forces in the earth’s mantle could move the giant Let’s suppose you’ve just heard a claim that sounds a little fantastic. landmasses. First, ask what evidence is provided. A lot? Very little? Keep in mind that quality rather than quantity is the critical factor. Then, how do you know Sifting through the claims the evidence is true? Someone said so? How are they qualified to know? While some wolves are hard to spot, many are not, if you know your Are their qualifications acceptable to other scientists? Then ask this. Is basic science. Claims that fly in the face of fundamental scientific knowl- the same evidence likely to show up if the test is tried again? edge are just not likely to be true. Those who want to believe the claims How were the results of the tests published? Wolves typically don’t often ask, “But how can you be sure that there aren’t unknown, undiscov- publish their results in respected scientific journals. In order to get pub- ered forces that might explain this?” We can’t be sure. But we can reply, lished in a mainstream journal, the work must be peer- “Just because something might be true, doesn’t mean that it is true.” reviewed by several other scientists. And even after it is Scientists are by nature skeptical—often still asking questions when published, other scientists will try to repeat the experi- others are willing to join the crowd. And they turn up in some ments to see if they can get similar results. unlikely places. The famous Hungarian magician Harry Hou- Wolves often just write books or articles without dini, born in 1874, astonished audiences by escaping from allowing skeptics to have a look before publishing. Why? handcuffs, straitjackets, and prison cells, even receiving U.S. Because they can. Anyone who can afford paper and ink patents on some of his elaborate devices. But he was both- can publish. Even more affordable is the Internet, which ered by the fact that few people could separate reality from

PHOTOS COURTESY OF MAGICTRICKS.COM provides an easy means for throwing out untested illusion. In his later years, Houdini put his extensive knowl- notions. (See “Question From the Classroom” in this edge of the occult and magic to public benefit by exposing issue of ChemMatters for one good example.) the tricks of fraudulent spiritualistic mediums. Houdini left Science isn’t perfect, but it has an excellent track his entire library of magic to the U.S. Library of Congress. record of weeding out incorrect notions. Scientists pride themselves in devising batteries of tests for screening Frank Cardulla taught chemistry at Niles North High School in Skokie, IL, before joining the staff of ChemMatters as Teacher’s Guide Editor. scientific-sounding claims. One of these devices is called the test of falsifiability. If I claim that REFERENCES Bauer, H. Science or Pseudoscience. University of Illinois Press: something is true, there should be some test for proving it is false. If you Champaign, IL, 2001. can think of no way to prove that what I am saying is false, then you had Shermer, M. Baloney Detection: How To Draw Boundaries Between better be skeptical. Science and Pseudoscience, Part I. Sci. Am., Nov 2001, p 36.

ChemMatters, FEBRUARY 2002 5 t looked so good at the pet store! You couldn’t wait to get home primary contributors. All animals accumulate nitrogen wastes as they and set up your own fish tank complete with colorful fish, little metabolize protein-rich foods. In humans and fish alike, processing and plants, and statues. But now the water is yellowish and cloudy. eliminating these toxic wastes keep the kidneys in business 24 hours a Even the fish seem different. They’re swimming slowly, spending more day. For a fish, getting rid of these wastes is simple. Just like a roadside time near the surface. Is that leftover food on the bottom? Smells funny. litterbug, a fish eliminates waste and simply swims away. In nature, rapid Looks like trouble. dilution in lakes, streams, and oceans keeps nitrogen compounds well Believe it or not, the problems you’re having with your home below critical levels. But in an aquarium tank, fish find themselves in aquarium tank are familiar to the professionals who manage large close and personal contact with their accumulating toxic wastes. aquarium exhibits—only on a much smaller scale. For your problems, Conditioning tank water to rid it of excess nitrogen challenges pro- a call to your pet store or an online search should provide some fessional aquarists and those of us setting up our home aquariums. It’s answers. You’ll also find staff members at large aquariums who are not difficult, but it takes a little patience, the right bacteria, and a few happy to lend advice. hardy fish to get it all started.

By Laura Ruth

Tom Ford, the senior aquarist at the UCLA The passage of nitrogen through an ecosys- Ocean Discovery Center in Santa Monica, CA, tem is referred to as the nitrogen cycle, or to be deals with problems similar to these every more technically correct, the nitrification day. According to Ford, “Cloudy yellow cycle. Fish excrete waste from the gills as water, fat and lazy fish, and food sitting on ammonia, some of which reacts in water the bottom or floating on the top of the to form ammonium ion. water are the three most common home Fortunately, there are widespread aquarium problems.” naturally occurring bacteria that readily Ford explains that the yellow color convert the ammonia and ammonium is due to waste products from the fish. ions to less toxic nitrite ions. But in a Among those products, ammonia (NH3) new fish tank, it takes time to get these + and ammonium ion (NH4 ), both color- bacterial colonies established. Experi- less, are particularly abundant. Fat and enced aquarists, professionals and hobby- lazy fish are simply signs of overfeeding. ists, advise putting two—no more than And the excess floating food harbors bacteria two!—nitrogen-tolerant fish in a new tank. that add their own organic wastes to the envi- (Goldfish are ideal for the job.) If you monitor ronment. Not only are overfed fish exposed to con- the water daily using a commercially available kit, taminated food, they may also suffer from exposure to you’ll notice a steady rise in ammonia levels. Just when the polluted water. you begin to fear for the lives of your brave pioneers, the A professional aquarist like Ford is responsible for maintaining the ammonia level plummets as the nitrite-forming bacteria take hold. chemistry of the tank water, preparing food, and delivering animal diets. But wait. It’s still to soon to buy those delicate and expensive fish. Aquarists agree that maintaining the water quality is fundamental to car- Keep monitoring, and you’ll soon see the nitrite levels skyrocket as bac- ing for aquarium animals. The salinity (saltiness), temperature, pH, dis- PHOTO BELOW BY MIKE CIESIELSKI. CENTER FROM PHOTODISC teria consume the available ammonia. Finally, another bacteria cohort – – solved oxygen, ammonia, nitrite (NO2 ), and nitrate (NO3 ) arrives. These bacteria thrive on nitrites, converting them to even less levels are carefully monitored to maintain water quality. toxic nitrates. And if you put plants in the aquarium, a good amount of Regulating the nitrogen these nitrates will be absorbed. Plants must be handled with care. Low load of the tank is particularly light means dead plants. These decay, releasing organic compounds that challenging since the fish cause another set of problems for water quality (see Figure 1). themselves are the Now you can add the fish! However, monitoring never stops. An ongoing problem, in even the most conditioned tanks, is pH fluctuation. With the accumulation of nitrates and organic acids, the combined byproducts of the living things in the tank, the pH steadily declines. It’s important to keep in mind that the pH scale is logarithmic. That means that while a pH change of 6.5 to 5.5 may seem small, it actually represents a 10-fold increase in acidity. Most fish tolerate a pH range between 6.5 and 7.5, but, even within that range, rapid

6ChemMatters, FEBRUARY 2002 www.chemistry.org/education/chemmatters.html changes of more than 0.3 in either direction are stressful. Professional Extra food aquarists monitor pH on a daily basis, either using colorimetric indicator solutions or electronic pH meters. Waste products How do you protect your aquarium fish from sudden pH changes? Fish The answer is “buffers”. You might think that mixing equal amounts of acid and tank water would yield a pH representing an average of the two separate pH read- ings. But this rarely happens. Seasoned aquarium tank water contains Plants Figure 1. – Nitrogen cycle sufficient bicarbonate ions (HCO3 ) to neutralize and absorb added acids in a fish tank and sufficient dissolved CO2 to neutralize added bases—acting together, Nitrosomonas

in effect, like pH sponges. bacteria ➞➞ – + CO2 + H2O ➞ H2CO3 ➞ HCO3 + H Carbonic acid Buildup of excess nitrate Nitrobacter Aquarists test their tanks bacteria regularly to monitor the buffer- ing capacity or carbonate hard- ness of the water. When the little bit high and may indicate that the water level is low as a result of capacity is low, the water is vul- evaporation. In that case, he adds more water. nerable to sudden variations in If you measure the salinity in our freshwater tank, you would look pH. for a reading around 4 ppt of salt, similar to what is normal for lakes and Like you, a fish needs oxy- streams. Hobbyists usually use simple and less expensive hydrometers gen for respiration. The aquarist, to measure the specific gravity of the water, which also increases as therefore, monitors the amount more salt is dissolved in the water. (See “How Dense Is It?”, page 10 for of dissolved oxygen (DO) in the directions for making one of your own.) water on a daily basis. Closely related to DO Senior aquarist Nancy Caruso monitors the tanks What kind of salt is in ocean water? Is it like sodium chloride monitoring is temperature monitoring. DO for nitrogen, pH, and (NaCl), the salt you put on your French fries? Sodium chloride makes up

COURTESY OF AQUARIUM OF THE PACIFIC; AKIRA KANEZAKI, PHOTOGRAPHER KANEZAKI, AKIRA PACIFIC; THE OF AQUARIUM OF COURTESY and temperature are related in two important dissolved oxygen levels. the largest percentage of salt in seawater, but other salts are important to ways. First, a fish, like all other cold-blooded marine life. The list includes magnesium chloride (MgCl2), potassium animals, has a metabolic rate that varies with its temperature. In warm chloride (KCl), and sul- water, the fish is livelier, metabolism speeds up, and oxygen demand fates of calcium and increases. But at the same time that the oxygen demand rises, the solu- magnesium. In fact, sea- bility of oxygen in water decreases. Under standard conditions, about 12 water contains more than mg of O2 dissolves in a liter of 10 °C water, while slightly less than 8 mg 75 inorganic elements, of O2 dissolves in a liter of 30 °C water (see Figure 2). their concentrations But with oxygen and other gases, there can be too much of a good ranging from many parts thing. Cold water and an overactive air pump can spell trouble. Gases in per thousand to mere the air, mainly nitrogen and oxygen, can saturate the tank water. As the traces measured in parts fish takes in this rich nitrogen and oxygen solution through its gills, tiny per billion. bubbles may form in the warmer blood vessels. The results can be fatal. If after a few trials At the Aquarium of the Pacific, Nancy Caruso, senior aquarist, mon- and errors, your aquar- itors the temperature of exhibits from a digital output. Ideal temperatures ium becomes your pride vary for exhibits from different ocean environments. For Northern Pacific and joy, you might Figure 2. The amount of oxygen from the air that Ocean collections, the ideal water temperature is 50 °F, whereas Tropical will dissolve in water decreases as the air want to think about a Pacific exhibits require a warmer 78 °F. For the UCLA Ocean Discovery temperature increases. (Source: Chemistry in the career in aquarium Center aquarium exhibits that use Santa Monica ocean water, Tom Ford Community, 4th Edition) technology. In the 10th looks for temperature readings of about 60 °F. To keep DO within accept- grade, Nancy Caruso shadowed an aquarist at the National Aquarium in able limits, tank water passes through large pumps that continually aer- Washington, D.C., and found that this was the job for her. Today, she ate the water. enjoys her work at the Aquarium of the Pacific. “It is rewarding to see To check the salinity, or saltiness, of the water, professional marine [my] animals doing well and people enjoying my exhibits.” And her co- aquarists like Ford and Caruso use an instrument called a refractometer. workers? “Biologists are generally really fun people!” When light passes from the air into another transparent medium like a salt solution, the path of the light rays bends. For ocean water, the abun- Laura Ruth is a science writer who lives in Los Angeles, CA. dant chloride ions actively rotate the incoming light. Thus, as the salt REFERENCES concentration increases, the degree of bending increases. Ford places a www.actwin.com/fish/mirror/begin.html. Aquarium hobbyists maintain sample of tank water into the chamber of the refractometer, holds it up this Web site, which offers valuable background and start-up advice (accessed December 2001). to the light, and reads the scale. The degree of light bending is indicated Chase, V. Nitrate in Ecosystems and Drinking Water. Carolina Tips, Oct on a scale that translates it into salinity in parts per thousand (ppt). Ford 1998, pp 1Ð3. [Available on the Web at www.carolina.com/tips/ looks for salinity readings of 30–35 ppt. A reading of 37 ppt would be a 98oct/tips1098a.htm (accessed December 2001).]

ChemMatters, FEBRUARY 2002 7 maple syrup

By Claudia Vanderborght ith steaming pancakes piled make glucose and release oxygen. Plants use In Vermont, the mountains are still deep high on his plate, Bugs Bunny the glucose to synthesize other organic mole- with snow when syrup producers begin to Wstrides to the maple tree and cules, such as cellulose for structure. Like work their trees. They drill a small hole into turns on the tap. Syrup gushes from the tree, most organisms, plants depend on glucose for each maple and then hammer in a plastic smothering the pancakes with sticky-sweet meeting their energy needs. spout. Pretty soon, the woods are filled with maple flavor. Anyway, that’s how it works in In animals, blood carries nutrients dozens of covered buckets hanging from cartoons. throughout the body. In a tree, sap transports spouts. In commercial operations, plastic tub- In the real world, 95% of all our genuine the nutrients. Tree sap may flow all year long ing is strung from tree to tree, ready to collect maple syrup is produced in just six New Eng- in the tropics, but in northern climates, the sap the sap and direct it into large storage contain- land states and three Canadian provinces. Even stops moving in the winter. As the spring sun ers. Then in late February or early March, when though maple trees grow all over the world, warms the tree, sap resumes its flow, distrib- daytime temperatures are warm but nighttime producing sugar through photosynthesis, only uting nutrients to the branches and buds. temperatures still drop below freezing, maple four varieties make enough sweet sap to be Ultimately, sap production depends upon sap starts flowing. harvested and boiled down into syrup. Of the weather. The sunnier the previous sum- At least once a day, the buckets contain- these, the one that covers the northeast with mer, the colder the winter, and the more vari- ing sap must be collected and transported to its blaze of autumn color—the sugar maple able the temperature during the spring thaw, the sugar house—not an easy task. The (Acer saccharum)—produces the sweetest sap the better the quantity and quality of sugary ground is snowy or muddy, and tree sap is of all. sap. On a warm day at the beginning of the heavy! Watery and barely sweet, maple sap All green plants gather in carbon dioxide sugar season, one large tree can produce 50 weighs about what water does, approximately through their pores and water through their liters of sap. But within two to six weeks when 1 kilogram per liter, or eight pounds per gal- roots. Chlorophyll harnesses the sun’s energy leaf buds swell, the sap begins to taste lon. Ask the many teenagers who work here. and uses it to drive the chemical reactions “buddy”. The brief season of collecting maple Carrying heavy buckets of sap down slippery,

PHOTO BY MIKE CIESIELSKI which combine carbon dioxide and water to sap is over. rocky slopes is hard work!

8ChemMatters, FEBRUARY 2002 www.chemistry.org/education/chemmatters.html From sap to syrup cup of syrup. The higher the hydrometer cools below its melting point. As the mole- floats, the denser the solution. (See page 10 cules lose kinetic energy, they fit together to At the sugar house, the sap is boiled to for directions for making and calibrating your form a precise pattern. Whether the crystal is a concentrate the sugar content by means of a own hydrometer.) rock made from molten lava or a snowflake process that hasn’t changed much in the hun- made from atmospheric moisture, its actual dreds of years since Native Americans first Making it pure and size and appearance are affected by the same taught the European settlers. Sap, which aver- sweet variables: the purity of the liquid substance, its ages 3% sugar and 97% water, is poured into concentration in the solution, the rate at which shallow evaporators. Good evaporators While it’s still hot, the maple syrup is it is cooled, whether the solution is agitated spread the sap out into a thin film, bringing it poured through thick felt filters to remove an while cooling, the presence of seed crystals, close to the heat. Great clouds rise up from impurity called sugar sand. Sugar sand is pro- and the chemical composition of the sub- the evaporator. Pretty soon, a thick fog and the duced when calcium and magnesium ions, stance itself. Candy makers manipulate these smell of maple fill the sugar house. dissolved in the heated sap, react with trace conditions to encourage different types of Evaporation is a physical change, but amounts of malic acid. As water is evaporated crystalline structures in their confections. boiling temperatures also bring about chemical from the sap, these salts also become more Very tiny crystals form when liquids are changes in the mixture. Soon after the sap concentrated in the syrup solution. Unlike first cooled without any agitation and then begins to boil, it becomes basic with a pH of 9. sucrose, calcium malate and magnesium stirred vigorously. To make a smooth maple But as chemical reactions continue to take malate are not very soluble and will precipitate spread or a creamy fudge, maple syrup is place, the pH slowly returns to a neutral 7. The out of the syrup. Sugar sand is gritty and, if heated to 112–113 °C (depending on altitude), colorless, transparent sap turns golden as the left in the finished syrup, will cause it to then gently poured onto a cooling slab, quickly sugars brown in carmelization reactions. Trace become dark and cloudy. bringing it to room temperature. Microscopic quantities of organic acids and amino acids crystals form when the cooled syrup is react to give the syrup its unique maple flavor. whipped vigorously into a creamy product. The best evaporators boil water off Large crystals form when a hot solution rapidly. The longer the sap is heated, the is allowed to cool gradually followed by less darker its color and the stronger its flavor. vigorous stirring. Maple sugar is made by Toward the end of the boil, as the solution heating maple syrup to between 118 and changes from mostly water to mostly sugar, 122 °C. As the solution cools, the growing the density of the liquid increases. Now, the crystals continue to add more and more mole- heat source must be carefully monitored to cules. Rock candy pieces consist of single prevent the viscous syrup from boiling over or huge sugar crystals. burning. Depending on the sugar content, it For making some candies, you want to takes about an hour to boil down 30 liters of prevent crystallization. Adding a different sap into 1 liter of syrup. Or, in other words, the PHOTO COURTESY OF LAMOTHE’S SUGAR HOUSE, BURLINGTON, CT ingredient changes the purity of the solution two gallons of sap you hauled down the Finally, still hot, the maple syrup is and disturbs the precise crystal pattern forma- muddy mountain will yield one cup of finished poured into cans or bottles. Sealing the bottles tion. Including corn syrup or fats in the cooling syrup—about enough to cover a couple of while hot ensures the syrup is sterile, or free mixture disturbs the crystal growth patterns in stacks of pancakes. from microorganisms that can ruin the delicate different ways resulting in varieties of different Backyard producers often use candy ther- maple fragrance and flavor. Microorganisms candies. mometers to judge when their syrup is done. can also destroy the syrup at other steps dur- And after a long day hauling buckets and Since the original maple sap is primarily water, ing the sugaring process. Whenever warm tending the boiling syrup kettles, there is a the initial boiling point will be close to 100 °C. sunshine heats the metal buckets or plastic reward. A traditional favorite during sugaring But as water evaporates and the sugar concen- tubing, microorganisms thrive. Over time, they time is “Sugar On Snow”. All you do is ladle tration of the mixture increases, the boiling ferment the sap’s sugar into ethanol and acetic fresh hot maple syrup over packed pans of point increases. Actual boiling points are acid. If boiled down, fermented sap produces a new-fallen snow. The syrup solidifies immedi- affected by the fact that most sugar houses are dark brown, strongly flavored maple syrup, ately offering up a delicious chewy, mapley, in the mountains where atmospheric pressure which no one would buy. Daily collection of and ice-cold confection. is lower than at sea level. Boiling points depend sap, rapid processing into syrup, and the fre- on atmospheric pressure—the lower the pres- quent cleaning of all buckets and utensils are Claudia Vanderborght is a high school chemistry teacher and science writer in Swanton, VT. sure the lower the boiling point. For a success- critical for producing an unspoiled syrup. ful product, producers at any altitude just Maple syrup is not the only confection REFERENCES remember that the finished syrup should boil that can be made from maple tree sap. Maple Corriher, S. O. Cookwise. William Morrow & Co.: New York, 1997. about 4 °C higher than the original boiling sap. spread, maple candy, and maple sugar are also Mann, R. Backyard Sugarin’. The Countryman It’s also important that the finished syrup wonderful treats. By heating the syrup longer, Press: Woodstock, VT, 1991. has the appropriate density. Syrup that is too more water evaporates. When cooled, varieties Nearing, H. and Nearing, S. The Maple Sugar thin spoils quickly, and syrup that is too thick of crystals are left behind with actual sizes Book; Schocken Books: New York,1970. will precipitate sugar crystals when cooled. depending on the conditions surrounding this North American Maple Syrup Producer’s Manual, Bulletin 856. Koelling, M. R., and The density of the syrup is measured with a final step. Heiligman, R. l. B., Editors: Ohio State hydrometer, a device that can be floated in a Crystals form when a liquid substance University: Columbus, OH, 1996.

ChemMatters, FEBRUARY 2002 9 ACTIVITY:

n this activity, you will make and calibrate a hydrometer, an instru- face. Remove the hydrometer, Use your hydrometer ment used in aquarium technology and in maple syrup production and mark it using the same pro- Use your calibrated instru- Ito determine the relative densities of solutions. Since the amount cedure you used for the distilled ment to estimate the sugar con- of dissolved substance or solute in water affects the density of the solu- water. Repeat for the other stan- centration of some unknown tion, the hydrometer is a handy instrument for estimating the salt con- dard solutions. solutions at room temperature. tent of an aquarium tank or the sweetness of a syrup product. You should now have a Try a glass of flat soda (see the hydrometer calibrated for 5 Fizz-Keeper article for ways to Make your own water? Go ahead. Try it. Were you sugar concentrations—0%, 10%, obtain that in a hurry!), a fruit right? 20%, 30%, and 40% sucrose. punch, some maple syrup, or any hydrometer other sugar solution you have on Materials Calibrate your hand. Safety goggles (wear them when hydrometer a Discussion working with solutions) To make your hydrometer 1. Find a discus- 1 large plastic Beral pipette into a useful measuring instru- sion of density ment, you’ll need to calibrate it. Scissors in your chem- To do this, you will need to make 25 metal BBs istry textbook. Plastic cup some sugar solutions of known Use that discus- concentrations. Metric ruler sion to explain Marker Materials the behavior of the hydrometer Carefully cut off the tapered Balance in the series of end of the pipette, leaving the Distilled water standard solu- long straight stem attached to the Four 9-ounce clear plastic cups tions. bulb. Insert the 25 BBs into the Bag of granulated sugar (sucrose) opening and let them fall down One 250-mL beaker, graduated b 2. Why did the into the bulb (see photo a). or a measuring cup with a milli- directions spec- liter scale Try it out ify “room tem- The cup of water from the Fill a 9-ounce plastic cup to perature”? Why previous step is your control (0% within 1 cm of the rim with dis- did the direc- sucrose). tilled water. You’ll also need a tions specify We’ll make our standard metric ruler and a sharp tip per- “flat soda”? solutions according to the per- manent marker (laundry pen). cent mass dissolved in a given Carefully lower your volume of solution. hydrometer into the water. Don’t Do this. Weigh 25 g of sugar let it completely submerge. If it and place it in the beaker. Fill the PHOTO S BY MIKE CIESIELSKI submerges, remove one or two beaker to the 250-mL mark with BBs and try again. Allow a short distilled water, stir, and you have length of stem above the surface a 10% sugar solution (mass of the water. Measure it in milli- sugar/volume solution × 100). meters (see photo b). Remove the More things to try Pour the solution into a plastic hydrometer, dry it, and mark the ¥ After you estimate the sugar concentration of a sample of cup and mark the cup “10% stem at the point where it met the flat soda, weigh out the amount of sucrose needed to make a 250- Sucrose”. water’s surface. In a similar way, weigh mL volume at that concentration. Are you surprised at the amount Make a prediction 50 g sugar to make a 20% solu- of sugar that goes into making your soft drink? Now If you stirred sugar, any tion, 75 g sugar to make a 30% add enough sugar to the paper until you have amount that will dissolve, into solution, and 100 g sugar to enough to make a 12-ounce serving—the your cup of water, would you make a 40% solution. amount you get in a beverage can. Still thirsty? expect the hydrometer to sink Calibrate your hydrometer ¥ Make another hydrometer, and calibrate it using salt solu- lower beneath the surface, ride this way. Lower the instrument tions instead of sugar solutions. Are your results identical? higher in the water, or stay at the into the 10% solution. Measure Do they follow a similar pattern? same point it was in the distilled the length of stem above the sur-

10 ChemMatters, FEBRUARY 2002 www.chemistry.org/education/chemmatters.html ChemSumer

The Fizz-Keeper Does It Really Keep the Fizz?

By Brian Rohrig t’s been a long hard day, and you are short on energy law states that the solubility of a gas within a liquid is and long on thirst. You open the refrigerator, reach for directly proportional to the pressure of that same gas on the Ia cola, twist off the cap, and wait for the familiar liquid’s surface. Because there is such a large pressure of “whoosh” sound of escaping bubbles. Nothing. The soda CO2 gas in the headspace in a bottle of soda, a large amount has gone flat. You dump the contents down the sink drain. of CO2 remains dissolved in the soda. You settle for water. Any capped bottle of soda eventually develops a Sound familiar? Can’t someone invent a way to keep dynamic equilibrium. Every time a molecule of CO2 comes the fizz in 2-liter bottles of soda? There is a device that out of solution and enters the headspace, a molecule of CO2 claims to do just that. Appropriately, it’s called the “Fizz- leaves the headspace to go back into solution. As a result, a Keeper”, sold for just a few dollars at many department and constant amount of CO2 remains in the headspace once grocery stores. The Fizz-Keeper is a little pump that screws equilibrium has been established. onto the bottle in place of the cap. You use it to pump in If you insert a lit match into this space immediately outside air, thus increasing the air pressure in the bottle. It after opening a bottle of soda, the match will be extin- should work. Does it? guished. This is evidence that the headspace contains a Before we answer that question, let’s examine how fizz fairly high concentration of CO2, a gas that does not support is put into soda. At the bottling plant, carbon dioxide gas combustion. (CO2) is pumped into soft drinks under high pressures at As soon as a bottle of soda is opened, it begins to go low temperatures. Some of this gas combines with the flat. On opening, there is a sudden and dramatic reduction

water to form carbonic acid (H2CO3): of pressure—from more than 2 atm to 1 atm. With this ➞ decrease in pressure, molecules of CO immediately begin CO + H O ➞ H CO 2 2 2 2 3 coming out of solution. When enough of these molecules

But the majority of the CO2 gas simply stays dissolved collect, they form visible bubbles. Less dense than the sur- in the soft drink. When the top is screwed onto the con- rounding fluid, the bubbles rise straight to the top where tainer, some of this CO2 gas escapes into the headspace, they break the surface and pop. the “empty” space, above the soda. Escaped gas generally All of these CO2 bubbles coming out of solution give builds up to a pressure of over 2 atmospheres (atm) in a carbonated beverages their distinctive appeal. The fizz pro- typical 2-liter bottle of soda—that’s twice the pressure we duced by these popping bubbles produces a pleasant tin- normally experience at sea level. No wonder that new soda gling sensation in your mouth. Soda that has gone flat has bottles are so firm. Although carbonated beverage bottles lost its dissolved CO2, and once that’s gone—no more fizz. are designed to withstand 20 atm, many carry warnings on their labels, stating, “Contents under pressure. Cap may Goodbye, fizz

blow off causing eye or other serious injury. Point away Replace the cap, and CO2 once again accumulates in from face and people, especially while opening.” the headspace. Before long, there’s a new equilibrium It is the CO2 in the headspace that prevents the rest of between dissolved and gaseous CO2. But every time a bottle

PHOTO BY MIKE CIESIELSKI the CO2 in the bottle from coming out of solution. Henry’s is opened and then recapped, the pressure of CO2 in the

ChemMatters, FEBRUARY 2002 11 headspace will always be less than before, In my classroom, my students and I have because some of the CO2 has escaped. done this experiment many times, and we If some of the soda has been poured out, always get the same result. After 24 hours, the there will be a larger headspace. As a new soda that was simply capped is always fizzier! equilibrium sets up in the bottle, even more We conclude that the cap itself provides a CO2 comes out of solution. According to much better airtight seal than does the Fizz- Henry’s Law, a reduced pressure of CO2 above Keeper. However, we’ve found if you wait only the soda means less CO2 dissolves in the soda. a few hours, the two liquids are very similar in The result? Even less fizz when the bottle is fizziness. opened again. Why doesn’t the Fizz-Keeper work? Let’s So let’s give our new product a chance. go back to Henry’s law—this time, reading the What if after opening the 2-liter bottle of soda, fine print. Remember that the law relates the we use our new Fizz-Keeper to pump it up with solubility of a gas in a liquid to the pressure of air? Will the increased air pressure above the that same gas above the liquid. In other words, soda in the bottle keep more CO2 in solution? the only way to increase the solubility of CO2 in Will there always be fizz? Are our days of flat the soda is to increase the pressure of CO2 sodas over? above the soda. Simply pumping air (which contains very little CO2) above the soda has no Try this effect on how much CO2 stays in solution. Try this simple experiment. Take a previ- This isn’t easy to understand. Common ously opened bottle of soda, and shake it a lit- sense suggests that increasing the pressure of tle to produce a lot of foam. Now pump it up any gas above a liquid would help to keep any with the Fizz-Keeper. The foam goes away! It gas from escaping from solution. But this is looks like we’ve forced the CO2 back into solu- not the case. And we need yet another gas tion. Then open the bottle. It looks like the CO2 law—Dalton’s law of partial pressures—to remains dissolved. You don’t see the bubbles clear things up. coming right back out of solution. Our Fizz- Dalton’s law states that the total pressure Keeper works! Or does it? of gases in a container is equal to the sum of Close observation reveals that putting all the partial pressures in that container. If gas pressure on existing bubbles causes them to A and gas B are each exerting a pressure of shrink in size. The same thing can be observed 0.5 atm in the same sealed container, they will if you put some soap suds into a bottle and exert a total pressure of 1 atm, the sum of then attach a Fizz-Keeper. Pump the bottle up, their separate partial pressures. Now suppose and watch the foam shrink in size. Now you’re that gas A can be completely removed. Its seeing another gas law in action. Boyle’s law removal would have no effect on the partial states that as the pressure on a gas increases, pressure of gas B—it’s still 0.5 atm, no matter its volume decreases. So while it is true that what happens to gas A. Also, if more of gas A the Fizz-Keeper can shrink the size of existing is introduced into the container, this will have bubbles, you still don’t know whether it can no effect on the partial pressure of gas B. Even keep the soda from going flat. In other words, though the total pressure increases, the partial you still don’t know if all of that added air pres- pressure of gas B stays the same. sure will keep CO2 dissolved in the soda. Think about what happens in the head- space above a bottle of soda that was opened Now try this and then recapped. Immediately CO2 gas You’ll need to do still another experiment begins to diffuse out of solution into this to settle the whole thing. Take two bottles of space. In fact, CO2 gas continues to diffuse identical soda. Pour out half of the contents of into the space until equilibrium has been each one and then replace one with a normal reached. The partial pressure of CO2 that exists cap and the other with a Fizz-Keeper. Pump up at equilibrium in a bottle of soda depends only the bottle with the Fizz-Keeper until it is firm, on the total amount of CO2 present in the con- as the instructions state. Wait 24 hours and tainer, the volume of soda, and the volume of then feel both bottles. Is one firmer than the the headspace. It has nothing to do with how other? Pour some soda from each. Does one many other gases exist in this space. fizz more than the other? How does the taste Pumping in more ordinary air with its compare? Have a volunteer perform a blind generous supply of nitrogen (N2) and oxygen taste test to see if he can determine which is (O2) but scant amount of CO2 molecules just

PHOTOS BY MIKE CIESIELSKI the fizziest. can’t do the job. The pumped-in air has nearly Stop reading now if you’re going to try zero effect on how many CO2 molecules leave this. Then, read on when you’re finished. the soda and end up in the headspace. Only if

12 ChemMatters, FEBRUARY 2002 www.chemistry.org/education/chemmatters.html you had a way of pumping just CO2 into the headspace would you be able to keep CO2 in More things to try with the its place—in the drink. Other than buying a CO2 generator, is Fizz-Keeper there any way to keep a soda from going flat? You might try decreasing the empty space over the liquid. You can try squeezing the bot- aybe the Fizz-Keeper doesn’t keep carbonated beverages from going tle before capping to make the headspace flat. It still has some great uses in the lab. Here’s how to use it to smaller, or you can save some clean, smaller M demonstrate—you guessed it—gas laws! empty plastic bottles for storing the leftover soda. Less headspace means less CO2 will dif- How mass and volume affect density fuse out of solution. And where there’s CO2, You may have tried this at some point in your science career. Put a couple of there’s fizz. raisins in a container of carbonated beverage and see the raisins come to the top, break the surface, and plunge back to the bottom—over and over again. This is because bubbles of CO2 adhere to the raisins, increasing the volume of the combined raisin–bubble object while contributing little to its mass. When the raisin-bubble object reaches the surface, the bubbles pop and then the lone raisin, too dense to float, sinks to the bottom . . . picks up bubbles . . . and . . . well, you get the picture. But try this in a half-full bottle of soda. Put the raisins in, and watch the usual ups and downs. Then, put the Fizz-Keeper in place, and pump in as much air as you can. What happens? Do the raisins continue to bob up and down? We’ll let you explain this one. What do you think will happen if you remove the Fizz-Keeper, releasing the pressure? Try it. Then explain what you see. Hint: Take another look at Boyle’s law. Now try this In a container of fizzy soda, You need an ordinary small balloon and an empty 2-liter bottle. Put the balloon raisins rise when they collect bubbles and fall when the inside the bottle, and stretch the balloon’s open end up and over the bottle opening. bubbles break. Try blowing up the balloon so that it expands inside the bottle. Any luck? Now, place a bendable drinking Brian Rohrig teaches chemistry at Eastmoor straw in the bot- Academy in Columbus, OH. His most recent tle. With the straw ChemMatters article “Tattoo Chemistry Goes Skin Deep” appeared in the October 2001 issue. His protruding from book, 39 Fantastic Experiments with the Fizz- the opening, put Keeper, can be obtained directly from the author at the balloon inside [email protected]. the bottle and REFERENCES stretch the bal- Howald, R. The Fizz-Keeper: A Case Study in loon over the bot- Chemical Education, Equilibrium, and tle opening and Kinetics, J. Chem. Ed., Feb 1999, pp 208Ð209. the bent straw. Rohrig, B. 39 Fantastic Experiments with the Try inflating the Fizz-Keeper; Creative Chemistry balloon again. Concepts: Tallmadge, OH, 1999. Does it work any better? If you succeeded in inflating the balloon in the bottle, tie INTERNET REFERENCE off the open end and leave it in the bottle. Explain what you have experienced so far. The complete text of the patent for the Now, with the inflated balloon inside, attach the Fizz-Keeper to the bottle. What Fizz-Keeper (or any patented item) can be do you think will happen when you begin to pump? Try it, and then explain what found by accessing the U.S. Patent and Trade- you see. mark Office full text and image database at After pumping a few times, remove the Fizz-Keeper. What happens to the bal-

http://164.195.100.11/netahtml/srchnum.htm. PHOTOS BY MIKE CIESIELSKI loon? Again, explain what you see. The U.S. patent number for the Fizz-Keeper is 4,723,670.

ChemMatters, FEBRUARY 2002 13 By Michael Tinnesand t could be a scene from the latest Hollywood blockbuster: Revolutionaries attack the embassy and are about to ransack the ambassador’s office, looking for secret documents. They locate a file cabinet marked “Top Secret”, but as they open the drawer, Iit bursts into flames. All contents are utterly destroyed by blinding heat, hot enough to melt iron. Just another macho action thriller? Interestingly enough, such devices actually exist and are part of government-issue office fur- nishings. The Army refers to them as “M-610 Incendiary File Destroyers”. You might imagine the chemical reaction responsible for such an inferno to be a mixture of exotic and dangerous substances. The truth is that the files are destroyed by just the right combina- tion of aluminum metal and rust!

A history lesson temperatures as high as 2200 °C. Since the melting point of iron This simple but spectacular reaction between aluminum is 1530 °C, the iron produced in the reaction is actually molten! metal and iron oxide is called a thermite reaction. Thermite is a Dr. Hans Goldschmidt, a German chemist, discovered the generic name given to high-temperature reactions between cer- thermite reaction in 1895, while looking for new ways to obtain tain metal oxides and aluminum. For example, the thermite reac- metals from metallic ores. Humans have been refining metal tion described above is the single replacement reaction between ores for thousands of years. Most elemental metals are reactive iron (III) oxide and aluminum to produce alu- enough that we don’t find them lying around in nature, at least minum oxide and elemental iron: not for long. They tend to combine with the elements around them to make oxides, sulfides, and a great Fe2O3(s) + 2 Al(s) ➡Al2O3(s) + 2 Fe(s) + heat many other compounds. Because this reaction In refining metals the trick is to make releases heat energy, we call it those processes go in the opposite direction. We need to an exothermic reaction. And is “uncombine” the metal from whatever it has hooked up with. it ever exothermic! The When metals combine, they generally do so by giving up a few amount of energy released of their electrons to form bonds with other elements—a process is sufficient to produce called oxidation. To uncombine, they need to react with an ele- ment that can give electrons back to the metal—a process called reduction. The choice of the word “reduction” makes sense. The early chemists who coined the term were taking small moun- tains of metal ore and reducing them to much smaller amounts of pure metals. Goldschmidt gets credit for developing a new refining process using aluminum to reduce iron from ore. He also came up with the innova- tion of starting the reaction with a magnesium ribbon “fuse”. Why hadn’t anyone used aluminum to reduce metal oxides before? The answer is that until 1886, aluminum metal was very rare. It was almost impossible to refine or reduce aluminum from its ores. In 1886, Charles Hall, an Ameri- can (age 23), and Paul Heroult, a Frenchmen (also age 23), simultaneously and independently developed the process still in use today to make aluminum metal, leading to its much greater

14 ChemMatters, FEBRUARY 2002 www.chemistry.org/education/chemmatters.html H use in science and industry. It turns out that alu- A minum is very good at giving up its own electrons to id it other metals, causing them to be reduced. As a Sol ! result it is called a “reducing agent”. Other uses of thermite The thermite reaction has been used for a variety of applica- tions over the past 100 years, including metal welding, fireworks, Western movies, have long figured into human combat. Shells made weapons, and rockets. There are three good things about using thermite with magnesium casings filled with thermite are designed to strike and for welding metal. First, it generates a LOT of heat. Most kinds of weld- then burn very hot, starting more fires or melting and disabling the tar- ing technology depend on high temperatures to melt metal pieces so get. In fact, during the past two world wars, the only bomb dropped on they stick together. Second, the reaction produces liquid iron. This the United States by a foreign power was a 170-pound thermite bomb molten iron can be used to fill gaps between metal surfaces. And finally, dropped on Oregon in September 1942. Dropped by a Japanese Navy the thermite reaction can be float plane launched from a submarine, it was intended to start huge fires done in the field at remote loca- in the Oregon forests, thereby terrorizing the citizenry. But the thermite tions—making it ideal for use in bomb did little damage, probably thanks to the rain-soaked coastal cli- welding rails for railroad con- mate. struction. Another military application involved a slow-burning thermite. Car- Many high-speed railway tridges developed during the World War II were capable of heating cans systems use continuous track of soup and other foods while soldiers were in the field. consisting of long lengths of rail Thermite fires are generally difficult to extinguish. Unlike combus- welded together. The welding tion, thermite fires do not require oxygen from the air to start, so the typ- process starts by trimming the ical extinguishers using CO2 or noble gases to smother flames are not ends of the rails so that the gap very effective. And putting water on thermite reactions can be downright between them is about dangerous. The temperatures generated are high enough to decompose 1 inch. Next, a ceramic mold is water into hydrogen and oxygen, thus causing further explosions and placed around the gap. A more energy release. The recommended method of extinguishing ther- charge of thermite is placed in a mite is to cover the reaction with sand and to use mechanical means to large crucible above the gap. separate the reactants. Upon reacting, the thermite cre- ates a crucible full of molten Try it iron. When the bottom of the A full-scale thermite reaction is much too dangerous for classroom crucible is opened, molten iron or backyard demonstration. But you can get the idea by doing a scaled- flows into the gap to complete down version. First find two large, rusty iron balls. Old track-and-field the weld. But this description shotputs or large ball bearings (2–3”) are perfect—the rustier the better.

doesn’t come close to describ- PHOTO COURTESY OF D4 TRACK WELDING, WARMAN, SASKATCHEWAN Cover one of the balls with regular household aluminum foil. While wear- ing the heat and danger associ- Rails are welded with molten iron produced ing goggles and taking care not to smash a finger, strike the balls by a thermite reaction. ated with this reaction. Mighty together with a glancing blow. When they hit just right, you will see and thermite, indeed! hear a minithermite reaction at the point of contact. The heat and pres- sure of the balls striking together is enough for the reaction to happen at A solid reaction the point of contact. The resulting sparks and noise are like the results of One very interesting aspect of the thermite reaction is that it takes firing a toy cap gun. It may not be enough to destroy secrets or weld iron place in the solid state. Few reactions in nature occur between solids, rails, but you’ll get a glimpse of mighty thermite in action. and even when they do occur, they tend to go so slowly that they are rarely noticed. But once the thermite reaction starts, it quickly generates Michael Tinnesand taught high school chemistry in Hillsboro, OR, before enough energy to be self-sustaining. The reactants melt, allowing the becoming Head of K–12 Education at the American Chemical Society. rate to increase. REFERENCE

PHOTOS BY MIKE CIESIELSKI The military has used thermite to make incendiary bombs. Incendi- Feliu, A. L. Thermite Welding Gets High School Chemistry Class on ary weapons like the “flaming arrows” used to set wagons on fire in Track. J. Chem. Ed., Jan 2001, pp 15Ð16.

ChemMatters, FEBRUARY 2002 15

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