The Romans also stored wine and other beverages in lead containers and supplied their houses with water through lead pipes. Lead poisoning is cumulative. It affects the nervous system and the reproductive system as well as other organs. Initial symptoms of lead poisoning are vague but include restless sleep, loss of appetite, irritation, headaches, stomach-aches, and anemia. Brain damage, leading to gross mental instability and paralysis, develops. Some historians have attributed the fall of the Roman Empire to lead poisoning, as many Roman leaders, including the Emperor Nero, are reported to have exhibited these symptoms. Only the wealthy, aristocratic, ruling Roman class had water piped to their houses and used lead vessels for storing wine. Ordinary people would have fetched their water and stored their wine in other containers. If lead poisoning did indeed contribute to the fall of the Roman Empire, it would be yet another example of a chemical that changed the course of history.
Sugar—the desire for its sweetness—shaped human history. It was profit from the huge sugar market developing in Europe that motivated the shipping of African slaves to the New World. Without sugar there would have been a much-reduced slave trade; without slaves there would have been a much-reduced sugar trade. Sugar started the massive buildup of slavery, and sugar revenues sustained it. The wealth of West African states—their people—was transferred to the New World to build wealth for others.
Even after slavery was abolished, the desire for sugar still affected human movement around the globe. At the end of the nineteenth century large numbers of indentured laborers from India went to the Fijian Islands to work in the sugarcane fields. As a result, the racial composition of this Pacific island group changed so completely that the native Melanesians were no longer a majority. After three coups in recent years Fiji is still a country of political and ethnic unrest. The racial makeup of the population of other tropical lands also owes much to sugar. Many of the ancestors of present-day Hawaii’s largest ethnic group emigrated from Japan to work in the Hawaiian sugarcane fields.
Sugar continues to shape human society. It is an important trade commodity; vagaries in weather and pest infestations affect the economies of sugar-growing countries and stock markets around the world. An increase in sugar price has a ripple effect throughout the food industry. Sugar has been used as a political tool; for decades purchase of Cuban sugar by the USSR supported the economy of Fidel Castro’s Cuba.
We have sugar in much of what we drink and much of what we eat. Our children prefer sugary treats. We tend to offer sweet foods when we entertain; offering hospitality to guests no longer means breaking a simple loaf of bread. Sugar-laden treats and candies are associated with major holidays and celebrations in cultures around the world. Levels of consumption of the glucose molecule and its isomers, many times higher than in previous generations, are reflected in health problems such as obesity, diabetes, and dental caries. In our everyday lives we continue to be shaped by sugar.
4. CELLULOSE
SUGAR PRODUCTION promoted the buildup of the slave trade to the Americas, but sugar was not alone in sustaining it for over three centuries. The cultivation of other crops for the European market also depended on slavery. One of these crops was cotton. Raw cotton shipped to England could be made into the cheap manufactured goods that were sent to Africa in exchange for the slaves shipped to plantations in the New World, especially to the southern United States. Profit from sugar was the first fuel for this trade triangle, and it supplied the initial capital for the growing British industrialization. But it was cotton and the cotton trade that launched rapid economic expansion in Britain in the late eighteenth century and early nineteenth century.
COTTON AND THE INDUSTRIAL REVOLUTION
The fruit of the cotton plant develops as a globular pod known as a boll, which contains oily seeds within a mass of cotton fibers. There is evidence that cotton plants, members of the Gossypium genus, were cultivated in India and Pakistan and also in Mexico and Peru some five thousand years ago, but the plant was unknown in Europe until around 300 B.C. when soldiers from the army of Alexander the Great returned from India with cotton robes. Arab traders brought cotton plants to Spain during the Middle Ages. The cotton plant is frost tender and needs moist but well-drained soil and long hot summers, not the conditions found in the temperate regions of Europe. Cotton had to be imported to Britain and other northern countries.
Lancashire, in England, became the center of the great industrial complex that grew up around cotton manufacture. The damp climate of the region helped cotton fibers stick together, which was perfect for the manufacture of cotton, as it meant less likelihood of threads breaking during the spinning and weaving processes. Cotton mills in drier climates suffered higher production costs due to this factor. As well, Lancashire had land available for building mills, land for housing the thousands who were needed to work in the cotton industry, abundant soft water for the bleaching, dyeing, and printing of cotton, and a plentiful supply of coal, a factor that became very important as steam power arrived.
In 1760, England imported 2.5 million pounds of raw cotton. Less than eighty years later the country’s cotton mills were processing more than 140 times this amount. This increase had an enormous effect on industrialization. Demand for cheap cotton yarns led to mechanical innovation, and eventually all stages of cotton processing became mechanized. The eighteenth century saw the development of the mechanical cotton gin for separating the cotton fiber from the seeds, carding machines to prepare the raw fiber, the spinning jenny and spinning throstles for drawing out the fiber and twisting it into a thread, and various versions of mechanical shuttles for weaving. Soon these machines, initially powered by humans, were run by animals or by water wheels. The invention of the steam engine by James Watt led to the gradual introduction of steam as the main power source.
The social consequences of the cotton trade were enormous. Large areas of the English Midlands were transformed from a farming district with numerous small trading centers into a region of almost three hundred factory towns and villages. Working and living conditions were terrible. Very long hours were required of workers, under a factory system of strict rules and harsh discipline. While not quite the slavery that existed on the cotton plantations on the other side of the Atlantic, the cotton trade brought servitude, squalor, and misery to the many thousands who worked in the dusty, noisy, and dangerous cotton factories. Wages were often paid in overpriced goods—workers had no say in this practice. Housing conditions were deplorable; in areas around the factories buildings were crowded together along narrow, dark, and poorly drained lanes. Factory workers and their families were crammed into these cold, damp, and dirty accommodations, often two or three families to a house with another family in the cellar. Less than half of children born under these conditions survived to their fifth birthday. Some authorities were concerned, not because of the appallingly high infant mortality rate but because these children died “before they can be engaged in factory labor, or in any other labor whatsoever.” When children did reach an age to work in the cotton mills, where their small size allowed them to crawl underneath machines and their nimble fingers to repair breaks in the threads, they were often beaten to keep them awake for the twelve to fourteen hours of the working day.
Indignation over ill treatment of children and other abuses generated a widespread humanitarian movement pushing for laws governing work hours, child labor, and factory safety and health, from which much of our present-day industrial legislation evolved. The conditions encouraged many factory workers to take an active role in the trade union movement and numerous other movements for social, political, and educational reforms. Change did not come easily, however. Factory owners and their shareholders wielded enormous political power and were reluctant to accept any decrease in the huge profits from the cotton trade that might result from the cost of improving working conditions.
A pall of dark smoke from the hundreds of cotton mills was a permanent fixture over the city of Manchester, which
grew and flourished along with the cotton trade. Cotton profits were used to further industrialize the region. Canals and railways were built to transport raw materials and coal to the factories and finished products to the nearby port of Liverpool. Demand grew for engineers, mechanics, builders, chemists, and artisans—those with the technical skills needed by a vast manufacturing enterprise with products and services as diverse as dyestuffs, bleaches, iron foundries, metalworks, glassmaking, shipbuilding, and railway manufacturing.
Despite legislation enacted in England in 1807 abolishing the slave trade, industrialists did not hesitate to import slave-grown cotton from the American South. Raw cotton, from other cotton-producing countries such as Egypt and India as well as the United States, was Britain’s largest import during the years between 1825 and 1873, but the processing of cotton declined when raw cotton supplies were cut off during World War I. The industry in Britain never recovered to its former levels because cotton-growing countries, installing more modern machinery and able to use less expensive local labor, became important producers—and significant consumers—of cotton fabric.
The sugar trade had provided the original capital for the Industrial Revolution, but much of the prosperity of nineteenth-century Britain was based on the demand for cotton. Cotton fabric was cheap and attractive, ideal for clothing and household furnishings. It could mix with other fibers without problems and was easy to wash and sew. Cotton quickly replaced the more expensive linen as the plant fiber of choice for a vast number of ordinary people. The huge increase in demand for raw cotton in Europe, especially in England, led to a great expansion of slavery in America. Cotton cultivation was very labor intensive. Agricultural mechanization, pesticides, and herbicides were much later inventions, so cotton plantations relied on the human labor supplied by slaves. In 1840 the slave population of the United States was estimated at 1.5 million. Just twenty years later, when raw cotton exports accounted for two-thirds of the total value of U.S. exports, there were four million slaves.
CELLULOSE, A STRUCTURAL POLYSACCHARIDE
Like other plant fibers, cotton consists of over 90 percent cellulose, which is a polymer of glucose and a major component of plant cell walls. The term polymer is often associated with synthetic fibers and plastics, but there are also many naturally occurring polymers. The word comes from two Greek words, poly meaning “many” and meros meaning “parts”—or units—so a polymer consists of many units. Polymers of glucose, also known as polysaccharides, can be classified on the basis of their function in a cell. Structural polysaccharides, like cellulose, provide a means of support for the organism; storage polysaccharides supply a way of storing glucose until it is needed. The units of structural polysaccharides are β-glucose units; those of storage polysaccharides are α-glucose. As discussed in Chapter 3, β refers to the OH group on carbon number 1 above the glucose ring. The structure of α-glucose has the OH at carbon number 1 below the ring.
The difference between α- and β-glucose may seem small, but it is responsible for enormous differences in function and role among the various polysaccharides derived from each version of glucose: above the ring, structural; and below the ring, storage. That a very small change in the structure of a molecule can have profound consequences for properties of the compound is something that occurs again and again in chemistry. The α and β polymers of glucose demonstrate this observation extremely well.
In both structural and storage polysaccharides, the glucose units are joined to each other through carbon number 1 on a glucose molecule and carbon number 4 on the adjacent glucose molecule. This joining occurs by the removal of a molecule of water formed from an H of one of the glucose molecules and an OH from the other glucose molecule. The process is known as condensation—thus these polymers are known as condensation polymers.
Condensation (loss of a molecule of water) between two β-glucose molecules. Each molecule can repeat this process again at its opposite end.
Each end of the molecule is able to join to another by condensation, forming long continuous chains of glucose units with the remaining OH groups distributed around the outside of the chain.
Elimination of a molecule of H2O between C#1 of one β-glucose and C#4 of the next forms a long polymer chain of cellulose. The diagram shows five β-glucose units.
Structure of part of a long cellulose chain. The O attached at each C#1, as indicated with an arrow, is β, i.e., is above the ring to its left.
Many of the traits that make cotton such a desirable fabric arise from the unique structure of cellulose. Long cellulose chains pack tightly together, forming the rigid, insoluble fiber of which plant cell walls are constructed. X-ray analysis and electron microscopy, techniques used to determine physical structures of substances, show that the cellulose chains lie side by side in bundles. The shape a β linkage confers on the structure allows the cellulose chains to pack closely enough to form these bundles, which then twist together to form fibers visible to the naked eye. On the outside of the bundles are the OH groups that have not taken part in the formation of the long cellulose chain, and these OH groups can attract water molecules. Thus cellulose can take up water, accounting for the high absorbency of cotton and other cellulose-based products. The statement that “cotton breathes” has nothing to do with the passage of air but everything to do with the absorbency of water by cotton. In hot weather perspiration from the body is absorbed by cotton garments as it evaporates, cooling us down. Clothes made from nylon or polyester don’t absorb moisture, so perspiration is not “wicked” away from the body, leading to an uncomfortable humid state.
Another structural polysaccharide is chitin, a variation of cellulose found in the shells of crustaceans such as crabs, shrimps, and lobsters. Chitin, like cellulose, is a β-polysaccharide. It differs from cellulose only at the carbon number 2 position on each β-glucose unit, where the OH is replaced by an amide (NHCOCH3) group. So each unit of this structural polymer is a glucose molecule where NHCOCH3 replaces OH at carbon number 2. The name of this molecule is N-acetyl glucosamine. This may not seem terribly interesting, but if you suffer from arthritis or other joint ailments, you may already know the name. N-acetyl glucosamine and its closely related derivative glucosamine, both manufactured from crustacean shell, have provided relief for many arthritis victims. They are thought to stimulate the replacement of or to supplement cartilaginous material in the joints.
Fields of cellulose—a cotton field. (Photo by Peter Le Couteur)
Part of the structure of the polymer chitin found in crustacean shells. At C#2 the OH of cellulose has been substituted by NHCOCH3.
Humans and all other mammals lack the digestive enzymes needed to break down β linkages in these structural polysaccharides, and so we cannot use them as a food source, despite the billions and billions of glucose units available as cellulose in the plant kingdom. But there are bacteria and protozoa that do produce the enzymes necessary to split the β linkage and are thus able to break down cellulose into its component glucose molecules. The digestive systems of some animals include temporary storage areas where these microorganisms live, enabling their hosts to obtain nourishment. For example, horses have a cecum—a large pouch where the small and large intestines connect—for this purpose. Ruminants, a group that includes cattle and sheep, have a four-chambered stomach, one part of which contains the symbiotic bacteria. Such animals also periodically regurgitate and rechew their cud, another digestive system adaptation designed to improve access to the β linkage enzyme.
With rabbits and some other rodents, the necessary bacteria live in the large intestine. As the small intestine is where most nutrients are absorbed and the large intestine comes after the small intestine, these animals obtain the products from the cleaving of the β link by eating their feces. As the nutrients pass through the alimentary canal a second time, the small intestine is now able to absorb the glucose units released from cellulose during the first passage. This may seem, to us, a thoroughly distasteful method of copin
g with the problem of the orientation of an OH group, but it obviously works well for these rodents. Some insects, including termites, carpenter ants, and other wood-eating pests, harbor microorganisms that allow them to access cellulose for food, with sometimes disastrous results for human homes and buildings. Even though we cannot metabolize cellulose, it is still very important in our diet. Plant fiber, consisting of cellulose and other indigestible material, helps move waste products along the digestive tract.
STORAGE POLYSACCHARIDES
Though we lack the enzyme that breaks down a β linkage, we do have a digestive enzyme that splits an α linkage. The α configuration is found in the storage polysaccharides, starch and glycogen. One of our major dietary sources of glucose, starch is found in roots, tubers, and seeds of many plants. It consists of two slightly different polysaccharide molecules, both polymers of α-glucose units. Twenty to 30 percent of starch is made up of amylose, an unbranched chain of several thousand glucose units joined between carbon number 4 on one glucose and carbon number 1 on the next glucose. The only difference between amylose and cellulose is that in amylose the linkages are α and in cellulose they are β. But the roles played by cellulose and amylose polysaccharides are vastly different.
Part of the amylose chain formed from loss of H2O molecules between α-glucose units. The linkages are α as the -O is below the ring for C#1.
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