THAT’S THE WAY THE COOKIE CRUMBLES (19 page)

I know from personal experience that it’s not fun to be covered with oobleck. It wasn’t supposed to happen. When I smashed my hand into that bowl filled with a slurry made of cornstarch and water, the stuff should have solidified immediately instead of splattering all over the place. And it would have, too, had I trusted what the physicists say and not hesitated before making contact. But I’m a chemist.

Dr. Seuss didn’t have physics or chemistry in mind when he wrote the children’s classic
Bartholomew and the Oobleck
back in 1949. It’s the story of the cranky King of Didd, who was dismayed that nothing but rain, snow, fog, and sunshine ever came down from the sky. The king ordered his magicians to cast a spell, and soon a green goop — oobleck — began to fall, covering the kingdom. Was the king happy? Of course not. You know that such wishes have a way of backfiring. Everything in the land turned sticky, and the royal subjects flopped and floundered about in the green goop. Only when the king admitted that he should have left nature alone did the oobleck dry up and disappear. It has, however, reappeared in many a children’s science experiment book. Oobleck is made by mixing a pound of cornstarch with about fourteen ounces of water to yield a truly yucky, but intriguing, mixture.

When you pick it up, oobleck just oozes out of your hand. But a quick squeeze converts it into a solid, which will maintain its form until you release the pressure. What’s going on here? The cornstarch is composed of tiny granules, very much like grains of sand. When the granules are moistened, water flows into the spaces between them and acts as a lubricant. The oobleck flows. If you suddenly apply pressure, however, the water squeezes out from the spaces between the granules, dramatically increasing friction. The oobleck now solidifies — at least until you allow water to flow back between the granules by easing the pressure. Now you see why punching a bowlful of oobleck should result in an unexpected effect. The substance should harden and not splatter. Alas, it takes a fair bit of courage to punch the gooey mess. Easing up before entry will make you look like the Pillsbury doughboy.

Those little cornstarch granules that make oobleck possible can also perform chemical magic of a much more practical variety. Way back in 1811, Russian chemist K.S. Kirchof discovered that cooking starch granules with dilute sulfuric acid produces a sweet syrup. He didn’t understand how it worked, but now we know that the acid causes the long chains of glucose molecules that constitute starch to break down into smaller fragments. The smallest piece formed is glucose itself, which, along with maltose (two glucose units), is perceived by our taste buds as sweet. Longer fragments, made of more glucose units joined together, have the effect of thickening the solution. These longer molecules have numerous atomic groupings (known as hydroxyl substituents), which can attract and bind water molecules. They also intertwine with each other. The overall result is that the motion of water molecules is impeded and the solution turns viscous.

Today, we rarely make corn syrup using the acid process. That’s because various fungi,
Aspergillus niger,
for one, produce enzymes that degrade starch in a more controlled fashion. If we desire a sweet syrup, then we have to increase glucose and maltose yields. To obtain thickness, we need many chains made of at least six glucose molecules. By using enzymes appropriately, we can meet these requirements. Corn syrup has myriad uses. Add a bit of maple flavoring and you have artificial maple syrup. A dash of red food coloring and some titanium dioxide produce great fake blood — the makers of the latest Dracula movie went through gallons of it. Add an enzyme extracted from some streptomyces bacteria and you’ve got one of the most widely used corn products: high-fructose corn syrup.

Fructose, commonly found in fruits, is chemically very similar to glucose, but it’s sweeter. As the bacterial enzyme converts glucose in the corn syrup to fructose, the sweetness increases. Most soft drinks today are sweetened with high-fructose corn syrup instead of cane sugar, because corn production is highly predictable, and the syrup is cheaper than sugar. Corn is an easy crop to grow. In North America, the acreage devoted to it is second only to that given over to wheat. Its various derivatives are present in over three thousand grocery items, and most of our livestock is reared on corn. Indeed, we consume about three pounds of corn each day in the form of meat, poultry, dairy products, and assorted other foods. Take a look at the label on a container of pudding or a jar of peanut butter. Chances are you’ll find cornstarch listed. In some cases, it’s modified cornstarch. This usually means that manufacturers have added certain reagents — phosphates, for example — to make some of the starch molecules cross-link. This joining together of the molecules to form a lattice affects the translucence, texture, stiffness, and moisture-holding capacity of the product. Unmodified cornstarch yields a loose pudding, whereas a spoon will stand up in a pudding made with modified starch. As if all these uses for corn weren’t intoxicating enough, consider that we can ferment corn mash to produce whiskey. And we can also use it to make gasohol.

How about plastics and fabrics made from cornstarch? The people at Cargill Dow, a chemical company in Nebraska, have found a way to convert corn into biodegradable plastics. They ferment cornstarch to produce lactic acid, which they then convert to polylactides — long chains of the acid. Presto! They have created a plastic that can be molded and spun into fibers, and it comes from completely renewable feed stocks. A wedding dress made completely from polylactides is already on the market. In this instance, people who insist that old-fashioned weddings are corny could be perfectly right.

My first trip to New York was in 1964. A couple of buddies and I decided we had to see the World’s Fair. When we arrived at the fair site in Flushing Meadows, we looked around and considered what attraction we should visit first. The longest line was in front of the Vatican pavilion, of all things. We joined it, figuring that all these people must know something. They did. Michelangelo’s magnificent
Pieta
was the pavilion’s centerpiece. For the first time in five hundred years, the Church had agreed to display the work somewhere other than Saint Peter’s Basilica, on the condition that its hosts take elaborate safety measures — such as placing the statue behind Plexiglas panels.

Being forced to view this glorious work of art through plastic did not sit well with the art critics. It gave one “a feeling of violation,” the critic for the
New York Times
said; the plastic made the
Pieta
look “helpless and cold.” Strange . . . that’s not the way I saw it. I marveled at the plastic: it was virtually invisible, yet so strong that it could withstand bullets. It was a plastic that could have altered the course of history if, just a year before, President Kennedy hadn’t refused to ride in a convertible shielded with it on that infamous visit to Dallas.

Plexiglas, or polymethyl methacrylate (PMMA), belongs to that class of substances we call polymers. These are long molecules made up of repeating units (monomers), much like a chain of many individual links. The links in this case are molecules of methyl methacrylate. In the 1920s, Dr. Otto Rohm, a German chemist, was the first to find a way of converting the liquid monomer to solid, clear sheets of polymer. And it probably never would have happened if he hadn’t developed an interest in dog poop.

When Rohm was working for the Stuttgart Municipal Gasworks in 1904, an unpleasant odor wafting into his office from a neighboring tannery would often annoy him. He knew that tanners softened hides by immersing them in pits of fermented dog dung, and he began to wonder whether there might be an alternative to this distasteful method. The smell was very much like that produced by some of the by-products of his own industry, so Rohm decided to investigate a synthetic alternative to canine excrement. He soon came up with one. “Oropon,” as he called the synthetic tanning agent, was an instant success. Rohm formed a partnership with Otto Haas, a businessman who had immigrated to America from Austria, and the two established the Rohm and Haas Company, which would become one of the most successful chemical-manufacturing firms in history.

With money rolling in, Dr. Rohm was able to devote time to his real interest: chemical research. He had earned his doctorate in 1901 by submitting a dissertation on the chemistry of acrylics, interesting substances made of raw materials isolated from petroleum or natural gas. Now, in the 1920s, Rohm picked up the threads of this research and discovered a way to join molecules of methyl methacrylate to make polymethyl methacrylate. The clear sheets of Plexiglas, as they named the novel substance, had obvious commercial appeal. They were transparent and strong, and they could be heat-molded into whatever shape one desired. Dr. Rohm was soon sporting the world’s first pair of glasses that had acrylic lenses instead of glass ones. This gave the Luftwaffe an idea. Why not replace glass windows in aircraft with shatter-resistant Plexiglas? An excellent proposition — but there was a hitch. It was impossible to produce methyl methacrylate, the required starting material, on an economically viable scale. The answer to this dilemma would come from across the Atlantic, from the chemistry labs at McGill University.

At McGill, William Chalmers had found a way to make methyl methacrylate from acetone and hydrogen cyanide, both of which were readily available. Chalmers knew that John Crawford, a chemist at Imperial Chemical Industries (ICI) in England, was working with acrylic polymers, and he suggested to Crawford that he try the new method for making methyl methacrylate. Crawford successfully scaled up the process, making the mass production of polymethyl methacrylate possible. ICI called it Perspex. The Royal Air Force, like the Luftwaffe before them, recognized the potential of the material. They were in the process of developing the Spitfire fighter, and it featured a canopy made of plastic-reinforced glass that the pilot could draw over his head. Perspex, however, would clearly be better. By 1936, a Perspex manufacturing plant was in operation at Billingham, and Spitfires with Perspex canopies began to roll off the assembly line. Next came the B-19 Douglas Superbomber, in which the bombardier compartment and the machine-gun turrets were made of Perspex, allowing their occupants unobstructed views.

Perspex, as used by the British and the Americans, and Plexiglas, as the Germans called it, was a tremendous improvement over glass, but it was not indestructible. Direct hits could shatter it and send tiny slivers flying everywhere. On occasion, slivers would lodge in a pilot’s eye. Under normal circumstances, a foreign substance in the eye causes terrible irritation, but British eye surgeon Dr. Harold Ridley noted that Spitfire pilots did not suffer this reaction. Somehow, their eyes tolerated this particular foreign material. Ridley now had a vision. Maybe this was the key to curing cataracts, those opaque deposits that form in the lens of the eye as we age. At the time, the only method of treating cataracts was surgically removing the lens and fitting the patient with “Coke bottle” glasses, which did the job that the natural lens had done. The widespread belief was that any kind of implanted lens was doomed to fail because the eye would reject it. But maybe it wouldn’t reject polymethyl methacrylate, Ridley thought.

In 1949, Ridley carried out his first successful Perspex implant. The plastic performed well, but the surgical techniques were not refined enough. Lenses would often slip out of place, and the trauma of the surgery led to all kinds of complications. Most of these problems were eventually solved by the Dutch ophthalmologist Dr. Cornelius Binkhorst, who had studied under Ridley. It was from Binkhorst, in 1967, that Montrealer Dr. Marvin Kwitko learned the fine points of lens implantation, and Dr. Kwitko went on to pioneer the procedure in Canada. Although people initially greeted the innovation with skepticism, by 1975, Kwitko had demonstrated the viability of lens implantation and had begun offering a training course. Eventually, hundreds of ophthalmologists from across Canada and the U.S. would take the course and learn the fine points of cataract surgery and lens implantation.

The progress we have seen in cataract surgery has been truly phenomenal. It wasn’t very long ago that cataract patients had to lie for weeks in their hospital beds, surrounded by sandbags to prevent them from moving. Today, doctors perform cataract surgery on an outpatient basis, and it usually takes them no more than fifteen minutes. They emulsify the natural lens with an ultrasonic probe so that they can remove it through an incision so tiny it doesn’t even require sutures. Then they insert the new lens through the same opening. Silicone has joined polymethyl methacrylate as a material for lens manufacture, and researchers are working on developing lenses that can focus both near and far, perhaps eliminating the need for reading glasses after cataract surgery.

Chemistry, ophthalmology, and a good dose of serendipity have allowed many seniors to regain clear vision. I wonder if that
New York Times
critic who objected to viewing the
Pieta
through Plexiglas is now looking at the whole world through polymethyl methacrylate. If he is, I suspect that he doesn’t feel violated by the plastic lens.

The Virginia country road was narrow, and the visibility was poor. The Chrysler LeBaron pulled out to pass another car. It never made it: the LeBaron slammed head-on into an oncoming vehicle, also a Chrysler, with a terrifying crunch. Other drivers stopped and rushed over to the tangled heap of metal, fearing the worst. To their astonishment, both drivers crawled from their wrecked cars unhurt. The year was 1990, and for the first time ever, two vehicles equipped with airbags had collided.

The original idea for airbags was born in the fertile mind of none other than Leonardo Da Vinci. “Baghe di vento,” or “bags of air,” he called his invention, which he obviously hadn’t designed for cars. He’d designed it for flying men. Or, at least, for men who were attempting to fly. Da Vinci was fascinated by flight, and he dreamed of various flying machines, yet he was realistic enough to consider the risks. Brave men who strapped on wings, he thought, should also strap on bags of air to protect themselves should they fall from the sky like rocks.

But it was a different kind of rock that inspired the modern airbag in 1951. This rock was sitting in the middle of a road, and John Hetrick swerved to avoid it, ending up in a ditch. He was thankful that his daughter, who was sitting beside him, was unhurt, but he couldn’t help thinking about what would have happened if she had been thrown against the dashboard more forcefully. On the way home, Hetrick began dreaming of sponges and cushions that could offer protection in the event of a crash. A memory from his days as a navy torpedo technician popped into his mind. Hetrick recalled being directed to work on a torpedo in a maintenance shop. Torpedoes are propelled by compressed air. Suddenly, by accident, the compressed air in Hetrick’s torpedo was released. This was of no great consequence, but one detail of the occurrence stuck in Hetrick’s mind: the tarpaulin covering the torpedo had flown into the air.

Here was a possible solution to his crash-protection problem. Could he come up with a device that would fill a pillow with air in the event of a collision? Hetrick worked on the idea and constructed a prototype. In 1952, he was granted the first patent for what would become the airbag’s predecessor. The original idea of using compressed air turned out to be unworkable, because the air cylinder itself posed a risk. What if it was damaged in an accident and took off like a rocket? Furthermore, car manufacturers of that era were more interested in enticing customers with huge engines and tail fins than airbags. But as the slaughter on the highways continued unabated, carmakers began to realize that something had to be done. They installed seat belts, but most drivers didn’t use them. Then they gave serious consideration to airbags, but how could they construct a bag that could inflate within a few milliseconds of impact without using compressed gases?

They found their answer in a fascinating chemical called sodium azide (NaN
₃
). When ignited by a spark, this substance releases nitrogen gas, which can instantly inflate an airbag. The only problem was that the reaction also forms sodium metal, which reacts with moisture to generate sodium hydroxide, a highly corrosive substance. Thus, a burst airbag could wreak havoc. At this point, chemical ingenuity came to the fore. If they included potassium nitrate and silicon dioxide with the sodium azide, then the only products that would form in addition to nitrogen would be potassium silicate and sodium silicate. Both of these are inert, harmless substances.

An airbag is designed to release some gas just after it deploys; this helps cushion the body against impact. Hitting a fully inflated, unyielding airbag would be catastrophic. Before the carmakers started promoting their new protective device, they had to ascertain the safety of its contents. In the 1970s, Mercedes settled this issue by putting a cage full of canaries in a car and deploying an airbag. Canaries are extremely sensitive to toxic gases, but the birds survived the experiment. By the late 1980s, airbags had become a common feature in automobiles. They have since saved thousands of lives.

But, as there is with any scientific advance, there is a “but.” Airbags are not problem-free. While the chemistry involved in curbing sodium hydroxide production is clever, it isn’t foolproof. Airbags have released small amounts of the caustic material; in rare cases, this has caused severe eye injuries, even blindness. The most serious concern, however, is the damage that can be done by an airbag rocketing out at an astounding speed of up to 330 kilometers per hour. Those who sustain a blow to the head under these circumstances risk death. Tragically, over one hundred people, mostly children and small adults, have been killed in this fashion; some lost their lives in low-speed collisions that would not otherwise have been lethal. Many researchers are looking for ways to ensure that airbags inflate only when necessary, and that they are deployed in the safest possible way. They are exploring the use of sensors that can gauge a person’s weight, allowing a computer to calculate how and whether an airbag should be inflated. In any case, small children must never be allowed to occupy the front seat of an airbag-equipped car. Some researchers even argue that seat belts afford better protection than airbags.

There is a further problem that we need address. Sodium azide is more toxic than cyanide. What will happen to all the azide in cars headed for the junkyard? What if their azide canisters are not removed? If sodium azide is released, it can react with water to form hydrazoic acid, which is not only toxic but highly explosive as well. Sodium azide also reacts with metals such as copper or lead to form explosive copper or lead azides. Just ask the plumbers who were called to a lab where workers had been using sodium azide solutions. When they removed a piece of copper pipe and tossed it into the garbage, it exploded. An unfortunate and shocking way to learn about the chemistry of azides!