Dr. Joe and What You Didn't Know: 177 Fascinating Questions about the Chemistry of Everyday Lifeby Joe Schwarcz
From Beethoven's connection to plumbing to why rotten eggs smell like sulfur, the technical explanations included in this scientific primer tackle 99 chemistry-related questions and provide answers designed to inform and entertain.See more details below
From Beethoven's connection to plumbing to why rotten eggs smell like sulfur, the technical explanations included in this scientific primer tackle 99 chemistry-related questions and provide answers designed to inform and entertain.
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Dr. Joe and What You Didn't Know
177 Fascinating Questions and Answers about the Chemistry of Everyday Life
By Joe Schwarcz
ECW PRESSCopyright © 2003 ECW Press
All rights reserved.
DR. JOE AND WHAT YOU DIDN'T KNOW
1. How would you relate "barefoot, pregnant, and on a cactus" to cherry or strawberry ice cream?
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It all comes down to the fascinating little insect called dactylopius coccus.
When Hernán Cortéz arrived in Mexico in 1518, he was intrigued by the beautifully colored Aztec fabrics he saw there. The source of the dye appeared to be seeds on the surface of certain cactus plants, but closer scrutiny revealed that they were not seeds at all. They were little bugs. Today, we know these insects as cochineal and the dye they yield as carmine. Montezuma, the Aztec king, was so fond of wearing robes made of carmine-dyed fabric that he imposed a tax upon his subjects to be paid in dried cochineal insects.
The pregnant female cochineal bug produces the brilliant red dye that became the first product ever exported from the New World to the Old. Soon, Europeans were dying their wool and silk with the insect extract. Maybe the most memorable use of cochineal was the bright scarlets for which the Gobelin tapestries of Paris became famous.
Producing the dye is not an easy business. The female insects, which feed on the red cactus berries and concentrate the dye in their bodies and in their larvae, are scraped off the cactus and dumped into hot water, where they instantly die. They are then dried in the sun and crushed into a powder, which is added to water or to a water-alcohol mixture. For fabrics, a mordant, such as alum, which binds the color to the material, is generally used. Carminic acid, the active coloring agent, is one of the safest existing dyes, and it is commonly used in foods and cosmetics. Candies, ice cream, beverages, yogurt, lipstick, and eye shadow can all be colored with cochineal.
Allergic reactions to the dye are rare. There have been reports of people reacting to the aperitif Campari, pink popsicles, maraschino cherries, and red lipstick, but more people suffer reactions to other food and cosmetic ingredients. In one instance, the face of a little boy who was kissed by his loving grandmother became swollen. It seems he had been sensitized to carmine, probably through food or candy, and he had reacted to the coloring in her lipstick. When reactions do occur, they tend to be in the form of hives and swelling, although one anaphylactic reaction to Campari-Orange has been reported.
Cochineal insects are very small, so it takes about seventy thousand females to produce a pound of dye. The males are quite useless in this regard. Like the males of most species, they are duller than the females. They are also rare and live for only a week; during their lifetime, they mate with as many females as possible. (Maybe they are not so dull after all.) So, how do the dye makers separate the sexes? Well, the males can fly, but the wingless females cannot. When the cactus is disturbed, the males scoot, but the females cannot escape. They are scraped off, destined to color some of our cherry or strawberry ice cream. I know that many of you may not find the prospect of ice cream colored with bug juice appetizing, but it is an effective and safe dye. And, of course, it's all natural.
2. What condition would you have if you were being treated with carbamide peroxide?
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Stained teeth. Carbamide peroxide is the active ingredient in most tooth-whitening products, and it works by releasing hydrogen peroxide, which in turn yields hydroxyl free radicals, which can break down colored molecules.
Hydrogen peroxide itself is a liquid and difficult to apply to teeth, but when it's mixed with urea it forms a gel of carbamide peroxide that can easily be painted on teeth, placed into trays fitted to the teeth, or incorporated into whitening strips. Thickeners such as carbopol and glycerin are often used to achieve the right consistency.
Tooth discoloration is mostly the result of colored substances in foods and drinks that embed themselves over time in the calcium phosphate that makes up the tooth's outer coating, the enamel. Tannins in tea and coffee, anthocyanins in blueberries, and polyphenols in red wine are just some of the compounds that can discolor teeth. A further complication is that dentin, the mix of proteins and calcium phosphate that lies beneath the enamel, yellows naturally with age. The molecules responsible for tooth discoloration tend to have a network of carbon-carbon double bonds. Such unsaturated systems, as they are called, absorb some colors but reflect yellow. Hydroxyl radicals are highly reactive and can disrupt these double bonds, leading to whitened teeth.
Applying various peroxide products to the teeth is generally quite a safe and simple procedure, although some people experience heightened sensitivity to cold after their dentists apply products containing high concentrations of hydrogen peroxide. Products developed for home use generally contain only 3 to 6 percent hydrogen peroxide and do not cause sensitivity, but they may take weeks to lighten discolored teeth. We may not yet have an ideal system for treating stained teeth, but carbamide peroxide is surely a great improvement over historical methods, which included swirling with urine or rubbing the teeth with a mixture of chalk and ground rabbit skull.
3. By law, chlorofluorocarbons (CFCs) used as refrigerants in refrigerators must be removed before the appliances are discarded. This solves only part of the ozone-depletion and global-warming problem attributed to refrigerators. Why?
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The walls of refrigerators have to be heavily insulated to ensure efficient cooling. Typically, polyurethane foam insulation has been used for this purpose, and guess what it used to be blown with? Chlorofluorocarbons!
Foams are created by blowing a gas into a material to form bubbles. Of course, the gas must not react with the material, and, in the case of insulation, it should not transmit heat readily. CFCs, the substances already used as refrigerants, seemed ideal—at least until their environmental consequences were discovered. Legislation was then introduced calling for the removal of the refrigerant from all discarded refrigerators.
Most people would be surprised to learn that a far greater quantity of CFCs was used to make foam insulation for fridges than was used for refrigeration. A typical fridge may have a couple of hundred grams of refrigerant, but it can hold twice as much blowing agent captive in its insulation. And "captive" is the appropriate expression, because studies have shown that more than 90 percent of the original blowing agent is still present in a refrigerator fifteen years after it has been discarded.
Unless special methods are employed, the blowing agent is released into the atmosphere when such fridges are recycled for their metal content. Shredding the fridge into small pieces in an airtight chamber allows for recovery of CFCs. This technique is expensive, but it can have huge environmental benefits. Refrigerators manufactured these days do not present this problem. They contain cyclopentane as the insulating gas, and this has no effect on ozone depletion and a negligible effect on global warming.
CFCs as refrigerants were replaced in the 1990s by HFCs (hydrofluorocarbons), which do not damage the ozone layer but do contribute to the greenhouse effect. Some manufacturers are now switching to isobutane as a refrigerant, because, like cyclopentane, it has a minimal impact on the environment. Given that millions and millions of discarded fridges are piled up around the world, the problem associated with the CFC content of polyurethane foam insulation is not a trivial one.
4. Why does the common symbol for medicine depict a snake?
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A snake coiled around a staff is widely recognized as a symbol of healing. The staff belongs to Asklepios, the Greek god of medicine.
In ancient Greece, the sick would go to shrines called asklepieia, where priests would conduct healing ceremonies, often using sacred serpents. We don't know whether the snakes actually had a practical function in the treatment of disease or whether they just scared people into feeling better, but Italian researchers have examined the healing potential of the "four-lined snake," which is commonly found in Greece. An ancient relief depicting a wounded boy and the mouth of a large snake is what prompted the research. It turns out that snake saliva contains epidermal growth factors, which really may help heal wounds. Perhaps snakes are blessed with this chemical because their mouths are vulnerable to damage as they ingest their prey.
Sacred dogs were also kept in the asklepieia. Was it their job to lick wounds? There actually is some evidence that dog saliva, like that of snakes, contains epidermal growth factors. These substances induce healing by causing the proliferation of certain skin cells. Maybe that's why dogs are always licking themselves!
And what happened to Asklepios in Greek mythology? According to the story, the god of medicine was slain by Zeus because he feared that Asklepios would make all men immortal. But such notions were overturned by Hippocrates, who made the revolutionary suggestion that diseases were not caused by the gods and could not be cured by them.
Hippocrates initiated a process of careful observation and experimentation. He separated myth and magic from rational therapy. "Every natural event has a natural cause," he maintained. Hippocrates investigated symptoms and was able to predict the course of disease. But Asklepios's reliance on the healing power of snakes may yet turn out to have some merit. Proteins isolated from certain snake venoms have powerful anticlotting effects on the blood and may one day be used in the treatment of thrombosis.
5. In the late 1800s, fashionable ladies accentuated their derrieres by wearing bustles under their skirts. To further emphasize their protruding rear ends, many would bend forward as they walked, assuming a posture that came to be known as the "Grecian bend." What does this have to do with the construction of the Brooklyn Bridge?
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The workers who built the underwater foundations of the Brooklyn Bridge often experienced excruciating pain when they returned to the surface of the Hudson River. It caused them to double over, a little like the bustle-wearing women with their "Grecian bends."
Decompression sickness was what afflicted these workers, but they referred to it as "the bends." The gigantic pylons that support the bridge had to be constructed deep in the riverbed, and the construction workers labored in large, open-bottomed timber chambers, or caissons, on the floor of the Hudson. Inside these caissons, they toiled away, excavating soil and rock. The surrounding water exerted tremendous pressure on the chamber walls, so the air inside had to be pressurized to prevent the caissons from collapsing.
Since the extent to which a gas dissolves in a liquid is determined by the pressure exerted by the gas on the surface of the liquid (Henry's Law), at high pressures, more nitrogen (which makes up 80 percent of air) dissolves in blood. If the pressure is released too quickly, as it was when the bridge workers rose to the river surface, the nitrogen comes bubbling out of solution and causes the bends.
The risks of working in a chamber of compressed air at the bottom of a river were little understood in the late 1800s. Even the chief engineer of the bridge, Washington A. Roebling, didn't appreciate the severity of the problem. In 1872, after spending twelve hours breathing pressurized air in a submerged caisson, he lost consciousness and became permanently paralyzed from the waist down. Over a hundred other bridge workers were afflicted by the bends, and three died.
The same problem plagued the builders of the Holland Tunnel—the first subway tunnel under the Hudson—until E. W. Moir installed decompression chambers at the work site. Moir realized that a victim of the bends could be treated by being placed inside a high-pressure chamber. There he would remain until the nitrogen in his body was forced back into solution in the blood, to be released at a controlled rate—a slow decompression. By the time the Holland Tunnel was completed, in the 1920s, the situation was well in hand, and not a single worker died from the bends. The tunnel was designed so that workers had to pass through decompression chambers, and those working under high pressure were allowed to work only for short periods.
Robert Boyle, perhaps the greatest scientist of the seventeenth century, would certainly have appreciated this. It was he who noted that rapid decompression can cause previously dissolved gases to come out of solution. How did he prove it? He placed a snake inside a chamber, reduced the pressure, and observed a gas bubble forming in the snake's eye. Gas studies like this one led him to formulate Boyle's Law, which states that the volume of a gas is inversely proportional to pressure. If you want a demonstration of this law, blow up a small balloon and take it along on your next airplane ride.
6. What happens to the alcohol when wine changes into vinegar?
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Simple. It disappears, because it is the alcohol that gets converted to vinegar. But even simple answers like this one have interesting stories behind them.
When the alcohol in wine changes into vinegar, there are two processes involved. The first one is relatively minor. Ethanol, the alcohol of beverages, reacts with oxygen to form acetic acid, a dilute solution of which we refer to as vinegar. This happens only to a very small extent, because the wine doesn't come into contact with much oxygen. What really causes wine to turn to vinegar is contamination with a bacteria called Acetobacter aceti.
This very common bacterium produces an enzyme that converts ethanol to acetic acid. It can be found on the grapes used to make wine, but the most typical source of contamination is the fruit fly. That's why vintners take such elaborate measures to keep the little bugs out of their fermenting mixtures. Once Acetobacter bacteria get a foothold, they begin to multiply and soon form a cellulose-based, jelly-like substance called mother of vinegar. In the Philippines, this substance is regarded as a delicacy. A traditional Philippine sweet, called nata de coco or nata de pina, is made by mixing the bacterial cellulose with sugar.
In general, the conversion of alcohol in wine to acetic acid is considered undesirable. But not always. Wine vinegar is a popular gourmet grocery item. It's made by introducing mother of vinegar into wine to encourage the production of acetic acid. Many people prefer wine vinegar to regular vinegar because, in addition to acetic acid, it has numerous flavor compounds that were produced by the original fermentation.
It is possible, however, to make vinegar without using wine. Ethanol can be made from ethylene, which in turn is made from petroleum. The ethanol can then be converted to acetic acid by reaction with oxygen. Large amounts of acetic acid are produced industrially in this fashion. Diluting the pure acetic acid in water to a concentration of 5 percent produces vinegar. And if all you plan to do with the stuff is clean your boots or sprinkle it on your french fries, then it's good enough. But if you're having guests for dinner and serving up a salad, spring for the wine vinegar. And, for dessert, why not offer some nata de coco?
7. What are gel candles, and are they really dangerous?
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All kinds of horror stories travel around the Internet—such as the one about gel candles that explode and burn down your house. These stories are usually buttressed by the accounts of those who have "seen it happen." Well, the gel candle story is almost 100 percent bunk.
These candles have become very popular because they're pretty and they burn much longer than regular candles. Candle makers can also incorporate a diversity of fragrances and dyes into their gel products. The typical gel candle purchaser probably doesn't know that the candle's origins can be traced back over 1,300 years to something historians have referred to as "Greek fire"—which wasn't actually invented by the Greeks. This early version of a flamethrower was first used by the defenders of Constantinople in the seventh century; with a primitive pump, they sprayed hot oil—made sticky by the addition of tree resins—through a tube.
Excerpted from Dr. Joe and What You Didn't Know by Joe Schwarcz. Copyright © 2003 ECW Press. Excerpted by permission of ECW PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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