Curious Folks Ask: 162 Real Answers on Amazing Inventions, Fascinating Products, and Medical Mysteries - Sherry Seethaler (2009)

Chapter 2. Chemical concoctions

Sticky situations

I heard on some science TV show that no one knows for sure what makes glue work. Is this true? What does make glue stick? Does it depend on the type of glue? What do glues have in common?

We take sticky notes, glue sticks, Super Glue, and tape so for granted that it may come as a surprise that developing new adhesives is a very active area of research. Understanding what makes stuff sticky is key to making stickier adhesives or adapting them to new purposes.

Although people use the words glue and adhesive interchangeably, glues, which are made from natural materials, have been around a lot longer than adhesives, which are made from synthetic materials. According to archaeologists, ancient civilizations used sticky materials like tree sap to repair broken pottery as far back as 4000 B.C. Beeswax and tar were long used to seal gaps between planks in ships, and for centuries other glues have been made from fish, animal hides, and hooves.

White glues (adhesives), such as Elmer’s, work by evaporation. As the water in Elmer’s evaporates, the polyvinyl acetate latex that has spread into the crevices of the material being glued forms a pliable bond.

Super Glue has as its main ingredient a chemical called cyanoacrylate. The presence of water causes cyanoacrylate molecules to start linking with each other until they form a strong plastic mesh. Super Glue is all-purpose because pretty much everything has trace amounts of water on its surface.

Sticky notes are easily removable and restickable because the adhesive on the back of the notes consists of a thin, bumpy layer of microspheres. These little spheres stick to a surface, but the gaps between the spheres remain unstuck. In comparison to the pebbled appearance of the adhesive on the notes, the adhesive on tape looks flat and uniform under an electron microscope.

Even with synthetic sticky materials, scientists still have a thing or two to learn from Mother Nature. Geckos, with their amazing ability to run up walls, have been a recent source of inspiration. Geckos have about 500,000 microscopic hairs, called setae, on each foot. At the end of each seta are 1,000 branches tipped with pads called spatulae.

Unbalanced electrical charges around molecules in the spatulae and molecules in the surface to which the gecko is clinging interact, drawing the molecules together. These interactions, known as van der Waals forces, occur because electrons are mobile. At any instant, more electrons may be at one end of a molecule, giving that end a temporary negative charge, and the other end a temporary positive charge. This charge separation induces a movement of electrons in nearby molecules so that the charges fluctuate in synchrony, and the attraction is maintained over large numbers of molecules. Van der Waals forces, summed over the millions of spatulae in each foot, create a very strong bond.

Using this knowledge, researchers have developed a super-sticky material with “nanobumps” that resemble the spatulae on geckos’ toes. If it could be mass-produced, this material could be made into reusable tape that even works underwater.

Strong bond

Why is the adhesiveness of white glues, such as Elmer’s, stronger than that of glue sticks?

The sticky molecules in Elmer’s all-purpose glue are mixed with water, which allows the glue to penetrate into tiny gaps on an object’s surface. When the water evaporates, the sticky molecules remain behind and form many anchor points all over the surface. On the other hand, a glue stick glides over the pores and applies glue only to the bumps, resulting in fewer anchors.

The adhesive molecules in Elmer’s and glue sticks are different, but they bond in similar ways (unlike Super Glue, which chemically reacts with water to form a highly interlinked mesh of molecules). However, the ingredients used to solidify a glue stick and help it glide over a surface reduce its adhesive strength.

Black gold

How do you get gasoline, kerosene, and other products from crude oil? Also, how is it possible to make gasoline from corn?

Crude oil, when recovered from an oil well, consists of a complex mixture of hydrocarbons—molecules made from hydrogen and carbon atoms. To make products of value from this mixture, hydrocarbons of different sizes are separated via distillation.

This involves heating crude oil to over 1,000 degrees Fahrenheit (540 degrees C) at the base of a fractionating column—a tower 260 feet (80 meters) high with a series of collecting trays at different heights. The hydrocarbon vapor cools as it moves up the column and condenses on the trays. Larger hydrocarbons condense on the trays near the base of the column, and smaller hydrocarbons condense on the higher plates.

Methane, ethane, propane, and butane (which have one, two, three, and four carbons, respectively) are collected from the very top of the column. They can be bottled and sold. Since they are odorless, smelly sulfur compounds are added for safety reasons.

The fractions condensing on lower trays include gasoline, kerosene, gas oil (used for diesel fuel and heating oil), and lubricating oil. The very large hydrocarbons that do not boil off are redistilled at low pressure to separate waxes, tar, and so on.

Subsequent processing steps depend on consumer demand. For example, to increase the yield of gasoline from crude oil, small hydrocarbons can be linked to form longer ones, and large hydrocarbons can be “cracked” into smaller ones. Hydrocarbons are also the starting materials for plastics, herbicides and pesticides, detergents, textiles such as acrylic and polyester, dyes, and cosmetics.

Gasoline, by the time you pump it into your vehicle, is a complex mixture of 200 chemicals added to improve performance and help fuel burn more cleanly. For instance, hydrocarbons of different lengths and structures are added to boost the fuel’s octane rating. This reduces “knocking,” which occurs when gasoline ignites spontaneously by compression, instead of by the spark from the spark plug.

In the past, tetraethyl lead was also added to reduce knocking. It was banned because of health risks and largely was replaced by methyl tert-butyl ether (MTBE). Now ethanol is replacing MTBE because of health concerns over the latter.

Ethanol is the fuel that is produced from corn or other starches or sugars. It is made in the same way as moonshine, by crushing and fermenting the grain, followed by distillation. Most engines can run on a mixture of up to 10 percent ethanol in gasoline, and “flexible fuel vehicles” can accommodate blends of up to 85 percent ethanol.

What’s in a name?

Does it matter what brand of fuel you use in your car, insofar as engine performance and gas mileage are concerned?

Gasoline suppliers share pipelines, and different distributors fill up their tanks at the same terminals. Therefore, the gasoline itself is the same. The only difference between brands is the additives blended with the gasoline when it is loaded into tankers destined for a retail station. Major brands advertise that they use more or better-quality additives to control corrosion and the formation of deposits in the engine and fuel supply system.

However, an American Petroleum Institute representative was unaware of any independent testing that shows which brands are superior. In addition, since 1995, the U.S. Environmental Protection Agency has mandated the use of detergents in gasoline and has set performance standards to ensure that the detergents control engine deposits. Control of deposits enhances fuel economy and reduces pollutants in engine exhaust.

Under the Clean Air Act and its amendments, the composition of gasoline has undergone many changes. First was the phaseout of leaded gasoline. Average blood lead levels in the United States declined dramatically over the 15 years that the use of leaded gasoline dropped from its peak to near zero, reports the Centers for Disease Control and Prevention.

Later came the introduction, in the most polluted cities, of reformulated gasoline with more oxygen to increase fuel combustion. Oxygen content is increased through the use of oxygenates. Initially methyl tert-butyl ether (MTBE) was used, but due to health concerns it is being replaced by ethanol. Reformulated gasoline has lower levels of benzene, a known carcinogen, and other pollutants. Fuel reformulation is determined by federal and local mandates, rather than by brand.

Fuel reformulation is not the only factor responsible for reductions in pollutants. A decade-long study of tailpipe emissions, published in the journal Environmental Science and Technology, determined that reductions in three major pollutants—carbon monoxide, nitrogen oxides, and hydrocarbons—were mainly the result of improved onboard vehicle emission control systems. The researchers found similar emissions improvements in cities that mandated reformulated fuel and those that did not.

Since the composition of the different brands of fuel varies little, many companies have tried to attract consumers by advertising their green credentials. For the Sierra Club’s environmental rankings of oil companies, see www.sierraclub.org/sierra/pickyourpoison.

Auto alternatives

As the world supply of fossil fuels dwindles, what alternatives to gasoline for vehicles are being researched or developed?

These days, the buzzword is biofuels—fuels derived from organic matter. The two most common biofuels are bioethanol and biodiesel. Bioethanol is made from starchy or sugary crops in the same process that yields homemade liquor. Yeast ferments sugar into ethanol, which is distilled to remove water. Biodiesel is made from vegetable oils or animal fats.

The United States has been ramping up production of ethanol from corn, but this cannot replace imported petroleum. Global corn prices have already increased as grain is being diverted from food chain to fuel tank. Corn is a difficult crop to grow, requiring high inputs of fertilizer and pesticides. According to some pessimistic estimates, it requires nearly as much energy to cultivate corn and convert it to ethanol as is obtained from the ethanol in the end.

On the other hand, there is a great deal of excitement about technologies to make ethanol from cellulose. Cellulose, the main structural component of plants, consists of long chains of sugars. An efficient process to convert cellulose into its component sugars would make feasible the production of ethanol from straw, crop waste, wood chips, and maybe even scrap cardboard and paper.

Hydrogen is another alternative source of energy for locomotion. Hydrogen can be burned or converted into electricity through fuel cells. Prototype hydrogen cars exist, but perversely, the hydrogen being used to power them is usually derived from natural gas. Hydrogen can be made by splitting water, but this requires a large input of energy. Storing and transporting hydrogen are also problems to be solved if hydrogen cars are ever to become practical.

Battery-powered electric vehicles are constantly improving. The major challenge in making them commercially viable is developing a battery that can power a vehicle for long distances, can be recharged repeatedly, and is not prohibitively expensive. The popular hybrid cars get around the limitations of batteries by combining gasoline power and electric power. Also, during braking, the electric motor in a hybrid car acts as a generator to recharge the batteries.

Hydrogen and batteries are essentially ways to store energy from other sources so that it can be used to move a vehicle. Other methods of energy storage are possible. For example, energy can be used to pump air into the pressurized tank of a compressed-air car. The expansion of air then moves the pistons in the engine. The car’s emissions are clean, but, of course, the actual emissions depend on how the energy used to compress the air was produced. Prototype compressed-air cars exist, but research is ongoing to bring them from concept to market. The greatest challenge is creating a car that can achieve a useful driving range on a single tank of compressed air.

Sugar high

I have heard that sugarcane is five to ten times more efficient than corn in the production of ethanol. Is this true? If so, why isn’t it being promoted?

Producing ethanol from sugarcane in Brazil is roughly seven times more efficient (with respect to the ratio of energy output to fossil fuel input) than producing ethanol from corn in the United States. However, more than this one statistic is needed to compare these two technologies.

Brazil’s sugarcane ethanol program began 30 years ago during the oil crisis. The government adopted mandatory regulations on the amount of ethanol to be mixed with gasoline, and it subsidized ethanol production, mainly through taxes on gasoline. Now Brazil is the world’s largest exporter of ethanol, and Brazilian ethanol is competitive with gasoline in international markets.

Sugarcane prefers warm climates, and in the United States the largest sugarcane producers are Florida, Louisiana, Hawaii, and Texas. American farmers also grow sugar beets in states with temperate climates. Currently, none of this sugar gets fermented into ethanol.

We eat all the sugar we produce, and we import another 20 percent of the sugar we consume. On average, each year every American gobbles down more than 40 pounds of refined sugar, nearly 45 pounds of corn-derived sweeteners, and just over a pound of honey and syrup. Annual per-capita sweetener consumption is the equivalent of about seven gallons of ethanol.

Because of the high cost of sugar in the United States, the domestic production of ethanol from sugar is not economically competitive with the production of ethanol from corn, according to data from the U.S. Department of Agriculture.

Brazil has an ideal climate for growing sugarcane, as well as low sugar prices. Despite these advantages, Brazil had a 15-year “learning curve” before its ethanol became cost-competitive with gasoline.

One reason for the efficiency of Brazilian sugarcane ethanol is that bagasse—the residue from sugarcane processing—is burned to provide heat for the distillation and electricity to run the machinery. Corn stover—stalks and leaves—could be used for this purpose, but it is not usually harvested.

The efficiency of corn-based ethanol could also be improved with the development of corn varieties that have higher starch content, or better enzymes to process the starch into sugar. In the meantime, the United States is protecting its corn-based ethanol industry with an import duty of 54 cents per gallon levied on Brazilian ethanol.

Both technologies raise concerns about the clearing of wild land for agriculture and the use of food to fuel vehicles.

Water fire

I received a video clip from a friend that deals with the use of water as an alternative to fossil fuels. Does this seem plausible to you? Neither of us can figure out why we haven’t heard of this before. It seems too good to be true.

The water-as-fuel hype recurs periodically. For instance, an Indian chemist convinced his local government that he powered his scooter on fuel made by boiling herbs in water. Then there was Stanley Meyer’s “water-powered car.” An Ohio court ordered Meyer to repay investors after it found him guilty of “gross and egregious fraud.”

One of the latest incarnations of water hype is a story on YouTube by a Cleveland-based television reporter about burning water. No, it is not the famous fire on Cleveland’s once grimly polluted Cuyahoga River, which helped spur the environmental movement. The video shows clean saltwater going up in flames.

The demonstration is not a hoax, but saltwater won’t reduce our dependence on other sources of energy. The adage “If it sounds too good to be true, it probably is” makes good sense. In order to burn, the water must be exposed to a strong, focused field of radio waves. When the field is turned on, the water burns. When it is switched off, the water stops burning.

In other words, unlike fossil fuels, water requires a constant input of energy to make it burn. No one has yet published an analysis that compares how much energy is recovered from burning the water versus how much is used to create the radio frequency field. However, it is impossible to extract net energy. It would violate the laws of thermodynamics and provide the basis for a perpetual-motion machine.

Water burns in the radio frequency field because it is being dissociated into hydrogen and oxygen, which are recombined by burning. The exact mechanism by which the field breaks bonds in water is under dispute, but the end result is similar to conventional electrolysis. Electrolysis uses an electric current to produce hydrogen and oxygen at separate electrodes, and more energy is used than is produced by burning the resultant hydrogen.

If using a radio frequency field to split water turns out to be more efficient than electrolysis, this new discovery could be of practical interest. Producing hydrogen from water is a way to store energy. If the sun is the source of energy to liberate hydrogen from water, the result is a clean-burning fuel produced by a renewable energy source.

Periodic-table personalities

Why are nuclear bombs so powerful? I know it has something to do with the splitting of an atom, but why does that cause such catastrophic damage?

There are two main types of nuclear bombs. In a fission bomb, large, unstable atoms (uranium or plutonium) split into smaller, more stable atoms. In a fusion bomb, also called a thermonuclear or hydrogen bomb, the nuclei of very small atoms combine to form larger, more stable atoms.

The binding energies that hold together the protons (positively charged particles) and neutrons (neutral particles) in the nucleus of an atom are approximately a million times stronger than the binding energies that hold together atoms in a molecule. Therefore, nuclear bombs are much more powerful than conventional bombs, in which chemical reactions—rearrangements of atoms in molecules—cause the explosion.

It might seem counterintuitive that opposite processes (splitting apart an atomic nucleus and fusing two nuclei) can both release energy. Whether fission or fusion releases energy depends on the size of the nucleus.

As atomic nuclei become larger, they grow more stable because of the strong nuclear force between nuclear particles. Atoms near iron (the 26th element) in the periodic table have the most stable nuclei. However, as atomic nuclei increase in size compared to iron, they become less stable, because there are more positively charged protons, which repel each other.

The more stable nuclei created by the fission of atoms larger than iron, or through the fusion of small atoms, have less mass than the original nuclei. The missing mass is transformed into energy, a process expressed mathematically by Einstein’s famous equation E=mc2.

Jolt-free beans

How is coffee decaffeinated?

The three main decaffeination processes are solvent decaffeination, decaffeination with carbon dioxide, and Swiss Water decaffeination. All three processes involve soaking the beans in chemicals to extract the caffeine.

Caffeine was first discovered and isolated in the late 19th century, and the first process to decaffeinate coffee, solvent decaffeination, was developed in Germany in 1900. The solvent is the liquid in which the coffee beans are soaked to remove the caffeine.

An ideal solvent removes the caffeine without removing compounds that give coffee its flavor and aroma. Many different (not always healthful) chemicals have been used to decaffeinate coffee, including alcohol, acetone, benzene, and methylene chloride, which was the preferred solvent until it was implicated in the depletion of the ozone layer. Ethyl acetate, a chemical that occurs naturally in some fruit, is now the preferred solvent.

In solvent decaffeination, the unroasted beans are steamed to make the beans more porous and the caffeine easier to extract. The beans are exposed to the solvent to dissolve the caffeine, and then they are rinsed, dried, and roasted.

Carbon dioxide decaffeination was patented in the early 1970s. In this method, carbon dioxide gas is compressed into a liquid at 50 times atmospheric pressure and is used as the solvent to extract caffeine. This method is particularly good at removing caffeine without removing flavor compounds, but a drawback is that it is expensive to build and maintain a carbon dioxide decaffeination plant. So the method is feasible for only large coffee producers.

Swiss Water decaffeination was patented in 1938 but was not commercialized until the late 1970s. In this process, coffee beans are soaked in hot water, which extracts the caffeine but also many of the flavor compounds. The water is passed through an activated carbon filter to remove the caffeine. Initially, the decaffeinated water was sprayed back on the beans after they had been partially dried to allow them to reabsorb the flavor compounds.

In the last 20 years, this procedure has been refined; now the caffeine-free water with the flavor compounds is used to remove caffeine from subsequent batches of beans. Since the water is already saturated with coffee flavor, the flavor compounds stay in the beans, but the caffeine is extracted.

Caffeine is one of many substances plants make to defend against insect attack. But the recent discovery of a caffeine-free variety of coffee related to commercially viable strains might ultimately permit plant breeding to render chemical decaffeination processes obsolete.

Decaf danger?

I was surprised to read about the chemicals once used in decaffeination, such as benzene, which I believe has been known (however, not really proven) to cause leukemia. Do I have the right chemical?

You are correct; benzene is a known carcinogen. Early efforts to decaffeinate coffee employed a number of other solvents now known or suspected to cause cancer, including chloroform, carbon tetrachloride, trichloroethylene, and methylene chloride.

In spite of this, even for those who were imbibing decaf before the newer methods of decaffeination started to emerge in the late 1970s, there is no evidence to suggest reason for alarm.

Only a very small amount of solvent (around one part per million) remains after the beans are rinsed and roasted. Methylene chloride, which was popular longer than the other solvents listed, appears to cause cancer in animals only when given in high doses (4,000 parts per million).

Also, studies that have compared decaf drinkers to those who drink regular brew have not shown an increased risk of cancer associated with drinking decaffeinated coffee.

Gently down the stream

There has been some coverage in the newspaper about a project of recycling wastewater in Southern California to make it drinkable again. If purifying wastewater is a lengthy and costly process, wouldn’t it be cheaper to do the same thing with seawater? Add to that the mental-health aspects associated with the concept of drinking what used to be wastewater.

It may seem surprising, but according to the City of San Diego Water Department, it currently costs about twice as much to desalinate seawater as it costs to take the same quantity of water “from toilet to tap.” The reason is that ocean water is about 25 times saltier than the starting point for recycled water.

Removing dissolved salts is the most energy-intensive step in producing drinking water. The more salt in the water, the more energy required to remove it. Salt removal is accomplished either via distillation or, more commonly, reverse osmosis. In reverse osmosis, water is pushed through a membrane that allows water molecules through, but not the dissolved salts.

According to a 2006 report by the Pacific Institute for Studies in Development, Environment and Security, the cost of desalinating water in California and delivering it to users may be as high as 1 cent per gallon and is unlikely to fall below one-third cent per gallon. Although considerably cheaper than bottled water, even the lower estimate is more than the price paid by most urban water users and is about 10 times the price paid by farmers in the western United States.

San Diego imports about 90 percent of its drinking water from Northern California and the Colorado River. As the costs of alternative sources of water rise due to drought and increased demand, desalination will become a more viable option. It already has in the Middle East, which is home to more than half of the world’s desalination plants.

In the United States, direct recycling of wastewater to drinking water is not accepted practice, probably for the psychological reasons you mention. On the other hand, indirect recycling of wastewater into drinking water is common. For example, cities upstream discharge treated wastewater into rivers that serve as the drinking water supply for cities downstream. Also, in some places, including Los Angeles and Orange County, recycled water is used to top off underground aquifers that supply drinking water.

Recycled water does not contain levels of bacteria, heavy metals, or organic compounds that exceed drinking water standards. However, levels of dissolved salts are higher than those in the drinking water supply.

In San Diego, recycled water is used mainly for irrigation. Some new high-rises are being built with a dual plumbing system via which the city supplies recycled water for flushing toilets. The dual system adds around 10 percent to the cost of installing the plumbing.

Water, water everywhere

In this age of scientific wonders, is there any chance of someone finding a method of converting seawater into freshwater economically? If and when that happens, what will we do with all the salt?

As population growth increases the demand on existing sources of freshwater, desalination of seawater is becoming increasingly economically viable. The worldwide market for water desalination is increasing about 15 percent annually.

Reverse osmosis, which involves forcing seawater through a membrane that allows only water molecules through, is the most popular desalination technology in the United States. Improvements in the membrane material that make it longer-lasting and less likely to clog are increasing its cost-effectiveness. The concentrated salt solution that remains behind typically is dumped back into the ocean.

Several new desalination technologies are being explored. Freeze separation involves freezing seawater to get ice crystals of pure water. In vacuum distillation, saltwater is vaporized at low pressure, which requires less heat than distillation at atmospheric pressure. In electrodeionization, seawater passes between two parallel membranes on the inside of oppositely charged plates. Because ions in the seawater are attracted to the plates, the sodium, chloride, and other ions are pulled out through the membranes, leaving behind pure water.

Reticent rubber

Recently my neighbor remarked that he has always wondered why automobile tire wear dust, although it must add up to a significant amount, never builds up enough to be seen. I told him that I read somewhere that tire dust was eaten by bacteria specialized in that strange way. Is that a fact, or was it someone’s imagination?

Tire particles do accumulate on the roadside and are washed away by rain. But it is also true that many kinds of bacteria and fungi degrade rubber. Natural latex rubber, which is produced by more than 2,000 species of plants to protect their wounds while they heal, consists of long chains of carbon atoms. Rubber-degrading microbes break down the chains using specialized enzymes. Recently some of these enzymes have been identified and the DNA sequence of the corresponding genes determined.

Three-quarters of all natural rubber harvested is used to make automobile tires. Softness and flexibility are ideal for nature’s bandage for trees, as well as products made from it, such as rubber bands, gloves, and protection for other body parts. However, tires must be more durable. Therefore, tires are made using variations of the vulcanization process invented by Charles Goodyear in 1839.

Vulcanized rubber is produced by heating natural or man-made rubber with sulfur and other chemicals. During the process, sulfur bridges form between the rubber’s carbon chains. Microbes have difficulty gaining access to the linked chains in vulcanized rubber. Vulcanized rubber is also a less hospitable environment to microbes, because it is less permeable to gases and water than natural rubber. Furthermore, some of the chemicals added during the vulcanization process are toxic. As a result, biodegradation of rubber, especially vulcanized rubber, is a very slow process.

Because scrap tires represent 12 percent of all solid waste, there is considerable interest in optimizing rubber biodegradation. Currently about half of waste rubber is combusted to generate electricity, or ground up and used in asphalt mixtures for road resurfacing. Vulcanized rubber can also be recycled by mixing fine particles of it with newly produced, nonvulcanized rubber, but the performance characteristics of recycled rubber are not optimal.

Recent research has shown that higher-quality recycled rubber can be produced by pretreating vulcanized rubber with bacteria that break sulfur bridges between carbon chains, which frees the carbon chains to form new links. Because researchers have discovered microbes specialized to cut carbon chains, microbes specialized to break sulfur bridges, and microbes that can detoxify vulcanized rubber, they are now exploring multistep approaches to bioremediation of tires.

On top of Old Smoky

Inside casinos I can see no cigarette smoke, but when I leave, my clothes smell like smoke. I then conclude I’ve been exposed to secondhand smoke. Am I wrong?

You are probably correct, because the thousands of chemicals in cigarette smoke give it a very recognizable smell. Assuming that no one is smoking inside the building, it is possible that people are smoking outside, near the air intake openings.

It would not take much smoke for you to be able to detect it. One study showed that about 3,000 cubic meters of fresh air (equivalent to the volume of about 10 spacious living rooms) is needed to sufficiently dilute the smoke from one cigarette to protect against eye and nose irritation. Also, the many fibers in fabric provide a large surface area to which smoke molecules can cling, so clothes tend to pick up the smell of smoke quite easily.

Odor eater

Baking soda does a remarkable job of neutralizing foul odors. How does it work?

Many unpleasant odors, such as those associated with vinegar, sour milk, and rotten eggs, are acidic molecules. Baking soda—sodium bicarbonate—is a weak base that can react chemically with acids to neutralize them. It can also react with a stronger base, so baking soda also neutralizes the basic molecules that cause fishy or ammonia smells.

The reaction between the baking soda and odor molecules is not visible, because not many molecules react at once. However, you can see the reaction if you mix vinegar and baking soda. The gas that bubbles off is carbon dioxide, which is formed during the reaction. This is the reason you may burp when you take antacids. Antacids are usually made of calcium carbonate, but their reaction with stomach acids is similar to the vinegar/baking soda reaction.

Exquisite earth

What exactly is terra preta, and what does it have to do with reducing global warming?

Terra preta is Portuguese for “dark earth.” It is a carbon-rich, highly fertile soil that covers as much as 10 percent of the Amazon Basin, an area as large as France. Terra preta is also found in other, mostly tropical, regions. Archaeologists used to think that this black soil was deposits from ancient volcanoes or pond bottoms. However, chemical analyses of the soil, as well as the consistent presence of broken pottery, have led most researchers to conclude that the soil is the result of human activity.

The indigenous people of the Amazon Basin, who must have been more numerous than once supposed, began the deposition of terra preta nearly 2,500 years ago, according to carbon dating. The darkest soils seem to contain a mixture of waste from human settlements. Incorporated into the slightly lighter surrounding soils are large quantities of charred organic matter, or char. Good char is produced not by slash-and-burn agriculture, but by plant matter smoldered slowly in a low-oxygen environment.

Crops grown in terra preta are twice as productive as those grown in nearby unaltered soil. The soil in the Amazon region typically is too poor to support sustainable agriculture. It is acidic, low in nutrients, and high in aluminum, which makes it toxic to soil microbes. Char reduces the soil’s acidity, makes the aluminum ions less reactive, and increases the soil’s capacity to retain nutrients. One study found that the bacterial diversity in terra preta was 25 percent greater than that in adjacent unaltered soil.

Ancient farmers were surely not thinking about global warming when they incorporated char into the soil, but it is a remarkably effective method to sequester carbon dioxide. Plants sequester carbon dioxide as they grow because they use it as a building block for the molecules that constitute wood. Unfortunately, when plants die and decompose, the carbon dioxide is released back into the atmosphere. In contrast, the black carbon from the char added by ancient farmers has remained in the soil for millennia.

Calculations by some researchers suggest that the creation of new terra preta could store more carbon each year than is emitted by all of current fossil fuel use. Efforts to incorporate char into large-scale farming are under way. One company has developed a contraption that converts farm waste into biofuel while producing char. But scientists do not yet have all the dirt on the ancient farmers’ tricks, such as what is the right type of char for each soil type.

Drug disintegration

Why does the effectiveness of vitamins, minerals, and medicines degrade over time? According to a pharmacist I asked, freezing does not keep them viable. Why not?

Freezing preserves food by interfering with microbial activity. But decay due to microbes is not the main problem for most medicines and nutritional supplements. Instead, over time, chemical reactions cause the degradation of the drug substance, the nondrug ingredients, or even the container, which may then leach chemicals into the medicine.

Reaction with oxygen in air (oxidation) and reaction with water (hydrolysis) are especially common modes of breakdown. Exposure to light, heat, and high humidity can increase the rate of drug decomposition. Accordingly, the bathroom medicine cabinet is a bad place to store medicine.

At least 90 percent of a medicine’s original potency must remain prior to its expiration date. Estimates of a medicine’s shelf life are based on standard conditions, but breakdown may be faster or slower, depending on the storage conditions. Breakdown products can be toxic, and their identity can vary depending on how the medicine is stored.

Proper disposal of unused medicines is critical because drugs are now widespread in waterways. Even if their concentrations are too low to affect humans, they may affect fish and other wildlife, and residues of antibiotics might encourage the development of drug resistance in bacteria. Unless your municipality has a pharmaceutical take-back location, the Environmental Protection Agency recommends disposing of medicines in the trash after mixing them with an undesirable substance such as kitty litter.

Lone nutrients

How are individual vitamins extracted or manufactured to put into pills or food supplements?

The first vitamin discovered, thiamin, was isolated at the beginning of the 20th century by soaking brown rice in water and separating the compound that dissolved. Nutritional compounds are still extracted from plant parts by bathing them with different liquids, such as alcohol, hydrocarbons, or water, and then distilling the resulting solution. The type of liquid selected for the extraction depends on the vitamin’s structure and whether it is water-soluble or fat-soluble.

It is cheaper to make vitamins than to extract them. Therefore, nearly all vitamins available commercially are manufactured. They are produced either through a series of complex chemical reactions perfected by chemists or by microorganisms that have been engineered to churn out large quantities of individual vitamins. They may also be made by a partnership of chemists and microbes, as in the case of vitamin C.

Vitamin C is produced in larger quantities than any other vitamin because, in addition to its use as a supplement, it is added to some cosmetics and is employed by the food industry to prevent the discoloration of food pigments. More than 100,000 tons of vitamin C is made annually. Most vitamin C producers use the Reichstein process, which dates to 1933. It transforms glucose into vitamin C in four steps, the first of which is accomplished by bacteria, and the subsequent three by chemists.

Vitamin B12 has a considerably larger and more complicated structure than vitamin C. The chemical synthesis of vitamin B12 involves about 70 steps, which makes it too technically challenging and expensive for industrial-scale production. Vitamin B12 cannot be extracted from plants either, because plants do not make it. However, many bacteria make vitamin B12 to catalyze reactions involved in fermentation. Genetically engineered bacterial strains that provide high yields of vitamin B12 are responsible for the more than 10 tons of vitamin B12 produced commercially each year.

Vitamin deficiencies were a pervasive health problem worldwide at the turn of the 20th century. In developed nations, programs established in the mid-20th century to fortify processed foods with vitamins have largely alleviated vitamin deficiencies. However, in developing nations, food processing and distribution are limited, and many staple crops, including corn, rice, and cassava, lack several vitamins. One approach to this problem is biofortification—breeding or engineering plants to produce additional vitamins. Progress has been made with biofortification of vitamin E, folate (vitamin B9), and beta-carotene (which our bodies can convert to vitamin A).

Rub-a-dub-dub

I know that soap in the 19th century was made from animal fat. How does a bar of soap made today differ from that made with animal fat? And how did early people bathe before they had soaps made from animal fat?

The earliest accounts of soap-making date from 2800 B.C., but the process seems to have been independently discovered by many different civilizations and may have been known even in prehistoric times. However, soap was initially used for purposes other than bathing, such as to prepare wool for dyeing.

Some early cultures did emphasize personal cleanliness, including the Romans and the Greeks, who rubbed themselves with fine sand and oil and removed the mixture with a metal instrument called a strigil.

Soap consists of linear molecules with an electric charge on one end, which can be created by treating animal fat with a strong base (such as lye). The charged end of the soap molecule is attracted to water. The neutral end is repelled by water and combines with oil. These properties allow soap (old-fashioned and modern) to help oil and water mix.

Soap-making was an established craft in Europe by the late 17th century. Soaps from southern France, Spain, and Italy, made from olive oil, were particularly renowned for their quality. However, soap was heavily taxed and thus considered a luxury item.

Until the mid-19th century, most American colonists, particularly those in rural areas, made their own soap by boiling lye extracted from wood ash with tallow—animal fat—which they saved all year. Because it was difficult to get the concentration of the lye just right, this method produced inconsistent results.

The first key advance in soap-making was the invention, in the late 18th century, of a more reliable method of producing a strong base.

The second key advance was the development, during World War I, of detergents. Detergents are made from petroleum, and detergent molecules can be tailored to have specific properties. For example, although soap binds with the calcium ions found in hard water and produces soap scum, detergents can be made that do not bind with calcium.

Many of today’s soaps are actually detergents, or a mix of detergents with soap derived from vegetable oils or animal fats, with added fragrances, moisturizers, and vitamins.

The plethora of cleansing products available and our modern obsession with personal cleanliness can be traced back to an advertising campaign for Lifebuoy soap, begun in the 1930s, that coined the term B.O.

Chore tech

How come I can use cold water in my washing machine but I have to use hot water in my dishwasher?

The reformulation of laundry detergents over the last few decades has made it possible to wash clothes in cold water and still get them clean. People traditionally have washed clothes in hot or warm water, but the increasing popularity of synthetic fabrics and the desire to reduce household energy consumption have fueled a trend toward cooler wash temperatures.

Fabrics get stained or dirty in three ways: Dirt gets physically trapped between the fibers, electrical attractions hold together the dirt and fabric molecules, or a chemical reaction occurs between a dirt compound and the fabric to form a new compound. In the latter situation, hot water may make a stain permanent by stimulating the chemical reaction. Otherwise, hot water makes it easier to separate dirt molecules from the fabric, because molecules jiggle around more when they are warmer.

Critical to the cold-water effectiveness of modern detergents is the inclusion of enzymes that chop up dirt molecules. The four major classes of detergent enzymes are proteases, lipases, amylases, and cellulases. Proteases work on protein-based stains such as grass, egg, and blood. Lipases work on fats and oils. Amylases remove starch-based stains such as potatoes, gravy, and baby food. Cellulases smooth the surface of cotton fabrics by cutting off the fuzz and tiny fibers generated by wear and washing.

Surfactants have also been modified to enhance cold-water laundering. Surfactants loosen dirt from fabric and suspend it in the wash. Like soap, they are molecules with a hydrophilic (water-loving) tail and a hydrophobic (water-hating) head. When the hydrophobic ends of a bunch of surfactant molecules glom on to greasy grime, they form micelles—tiny oil blobs dissolved in water thanks to the outward-pointing hydrophilic tails of the surfactant. Cold-water surfactants have heads that are extra-hydrophobic to help them better interact with oil, which dissolves more poorly in cold water.

Dishwasher detergent has also been reformulated to enhance cleaning and make it less harsh on dishes. Of course, dishwashers do not rely on agitation to help remove cooked-on food. Even more important, hot water helps destroy bacteria and viruses that could cause food-borne illnesses.

Hot water is still used for laundry when there is a risk of disease transmission, such as for hospital and hotel linens, but for the most part, high-tech suds allow us to save energy and preserve our favorite duds.