The chemical industry in the 20th century put a wide range of new materials at the disposal of society. It also succeeded in replacing natural sources of some materials. An important example of this is the manufacture of artificial rubber to meet a world demand far in excess of that which could be met by the existing rubber plantations. This technique was pioneered in Germany during World War I. In this effort, as in the development of other materials such as high explosives and dyestuffs, the consistent German investment in scientific and technical education paid dividends, for advances in all these fields of chemical manufacturing were prepared by careful research in the laboratory. Pharmaceuticals and medical technology
An even more dramatic result of the growth in chemical knowledge was the expansion of the pharmaceutical industry. The science of pharmacy emerged slowly from the traditional empiricism of the herbalist, but by the end of the 19th century there had been some solid achievements in the analysis of existing drugs and in the preparation of new ones. The discovery in 1856 of the first aniline dye had been occasioned by a vain attempt to synthesize quinine from coal tar derivatives. Greater success came in the following decades with the production of the first synthetic antifever drugs and painkilling compounds, culminating in 1899 in the conversion of salicylic acid into acetylsalicylic acid (aspirin), which is still the most widely used drug. Progress was being made simultaneously with the sulfonal hypnotics and the barbiturate group of drugs, and early in the 20th century Paul Ehrlich of Germany successfully developed an organic compound containing arsenic—606, denoting how many tests he had made, but better known as Salvarsan—which was effective against syphilis. The significance of this discovery, made in 1910, was that 606 was the first drug devised to overwhelm an invading microorganism without offending the host. In 1935 the discovery that Prontosil, a red dye developed by the German synthetic dyestuff industry, was an effective drug against streptococcal infections (leading to blood poisoning) introduced the important sulfa drugs. Alexander Fleming’s discovery of penicillin in 1928 was not immediately followed up, because it proved very difficult to isolate the drug in a stable form from the mold in which it was formed. But the stimulus of World War II gave a fresh urgency to research in this field, and commercial production of penicillin, the first of the antibiotics, began in 1941. These drugs work by preventing the growth of pathogenic organisms. All these pharmaceutical advances demonstrate an intimate relationship with chemical technology.
Other branches of medical technology made significant progress. Anesthetics and antiseptics had been developed in the 19th century, opening up new possibilities for complex surgery. Techniques of blood transfusion, examination by X-rays (discovered in 1895), radiation therapy (following demonstration of the therapeutic effects of ultraviolet light in 1893 and the discovery of radium in 1898), and orthopedic surgery for bone disorders all developed rapidly. The techniques of immunology similarly advanced, with the development of vaccines effective against typhoid and other diseases. Food and agriculture
The increasing chemical understanding of drugs and microorganisms was applied with outstanding success to the study of food. The analysis of the relationship between certain types of food and human physical performance led to the identification of vitamins in 1911 and to their classification into three types in 1919, with subsequent additions and subdivisions. It was realized that the presence of these materials is necessary for a healthy diet, and eating habits and public health programs were adjusted accordingly. The importance of trace elements, very minor constituents, was also discovered and investigated, beginning in 1895 with the realization that goitre is caused by a deficiency of iodine.
As well as improving in quality, the quantity of food produced in the 20th century increased rapidly as a result of the intensive application of modern technology. The greater scale and complexity of urban life created a pressure for increased production and a greater variety of foodstuffs, and the resources of the internal-combustion engine, electricity, and chemical technology were called upon to achieve these objectives. The internal-combustion engine was utilized in the tractor, which became the almost universal agent of mobile power on the farm in the industrialized countries. The same engines powered other machines such as combine harvesters, which became common in the United States in the early 20th century, although their use was less widespread in the more labour-intensive farms of Europe, especially before World War II. Synthetic fertilizers, an important product of the chemical industry, became popular in most types of farming, and other chemicals—pesticides and herbicides—appeared toward the end of the period, effecting something of an agrarian revolution. Once again, World War II gave a powerful boost to development. Despite problems of pollution that developed later, the introduction of DDT as a highly effective insecticide in 1944 was a particularly significant achievement of chemical technology. Food processing and packaging also advanced—dehydration techniques such as vacuum-contact drying were introduced in the 1930s—but the 19th-century innovations of canning and refrigeration remained the dominant techniques of preservation. Civil engineering
Important development occurred in civil engineering in the first half of the 20th century, although there were few striking innovations. Advancing techniques for large-scale construction produced many spectacular skyscrapers, bridges, and dams all over the world but especially in the United States. The city of New York acquired its characteristic skyline, built upon the exploitation of steel frames and reinforced concrete. Conventional methods of building in brick and masonry had reached the limits of feasibility in the 1800s in office blocks up to 16-stories high, and the future lay with the skeleton frame or cage construction pioneered in the 1880s in Chicago. The vital ingredients for the new tall buildings or skyscrapers that followed were abundant cheap steel—for columns, beams, and trusses—and efficient passenger elevators. The availability of these developments and the demand for more and more office space in the thriving cities of Chicago and New York caused the boom in skyscraper building that continued until 1931, when the Empire State Building, with its total height of 1,250 feet (381 metres) and 102 stories, achieved a limit not exceeded for 40 years and demonstrated the strength of its structure by sustaining the crash impact of a B-25 bomber in July 1945 with only minor damage to the building. The Great Depression brought a halt to skyscraper building from 1932 until after World War II.
Concrete, and more especially reinforced concrete (that is, concrete set around a framework or mesh of steel), played an important part in the construction of the later skyscrapers, and this material also led to the introduction of more imaginative structural forms in buildings and to the development of prefabrication techniques. The use of large concrete members in bridges and other structures has been made possible by the technique of prestressing: by casting the concrete around stretched steel wires, allowing it to set, then relaxing the tension in the wires, it is possible to induce compressive stresses in the concrete that offset the tensile stresses imposed by the external loading, and in this way the members can be made stronger and lighter. The technique was particularly applicable in bridge building. The construction of large-span bridges received a setback, however, with the dramatic collapse of the Tacoma Narrows (Washington) Suspension Bridge in the United States in 1940, four months after it was completed. This led to a reassessment of wind effects on the loading of large suspension bridges and to significant improvements in subsequent designs. Use of massed concrete has produced spectacular high arch dams, in which the weight of water is transmitted in part to the abutments by the curve of the concrete wall; such dams need not depend upon the sheer bulk of impervious material as in a conventional gravity or embankment dam. Transportation