The Stories of Two Chemicals

Take a moment to look around you. Where did all the stuff you see come from All the stuff in the universe is made from building blocks formed in stars such as the ones shown in the photo on the opposite page. And, as you learned in the DISCOVERY LAB, this stuff changes form. 

Scientists are naturally curious. They continually ask questions about and seek answers to all that they observe in the universe. One of the areas in which scientists work is the branch of science called chemistry. Your introduction to chemistry will begin with two unrelated discoveries that now form the basis of one of the most important environmental issues of our time. 

You are probably aware of some of the damaging effects of ultraviolet radiation from the Sun if you have ever suffered from a sunburn. Overexposure to ultraviolet radiation also is harmful to plants and animals, lowering crop yields and disrupting food chains. Living things can exist on Earth because ozone, a chemical in Earth s atmosphere, absorbs most of this radiation before it reaches Earth s surface. A chemical is any substance that has a definite composition. Ozone is a substance that consists of three particles of oxygen. 

Earth s atmosphere consists of several layers. The layer nearest Earth is the troposphere. The stratosphere Is above the troposphere. 

The troposphere extends to a height of about 15 km. Cumulonimbus clouds, or thun-derheads, produce thunder, lightning, and rain. 

A chemical is any substance that has a definite composition. Ozone is a chemical that is made up of three particles of oxygen. Ozone forms a thick blanket above the clouds in the stratosphere. This layer of ozone protects Earth from overexposure to ultraviolet radiation from the Sun. You are probably familiar with the damage that exposure to ultraviolet radiation can do to your skin in the form of sunburn. Ultraviolet radiation can also harm other animals and plants. In the 1980s, scientists documented that the ozone layer arovmd Earth was becoming measurably thinner in some spots. 

In the 1970s, scientists had observed that large quantities of chlorofluorocarbons (CFCs) had accumulated in Earth s atmosphere. CFCs are chemicals that contain chlorine, fluorine, and carbon. 

CFCs were used as coolants in refrigerators and air conditioners and as propellants in spray cans because they were considered relatively nonreactive. Some scientists hypothesized that there might be a connection between the concentration of CFCs in the atmosphere and the thinning of the ozone layer. 

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Hypothesis Let s return to the stories of two chemicals that you read about earlier. Even before quantitative data showed that ozone levels were decreasing in the stratosphere, scientists observed that CFCs were found there. Chemists Mario Molina and F. Sherwood Rowland were curious about how long CFCs could exist in the atmosphere. 

The story of DNA replication is followed by one of DNA modification. The most important chemical modification of DNA is methylation that is, the methyl group, CH3—, is added to two of the bases of DNA, adenine (A) and cytosine (C). Three modified bases are formed. 

The history of the substitution of hazardous chemicals could be considered a success story. If it is examined more closely, however, a range of as yet ume-solved tasks are still evident (cf chapter 6). This basically concerns two problem areas the fundamental ability and willingness to substitute hazardous substances and the question whether the substitute is actually any less dangerous. 

As in all history, the story of chemicals recalls past events and makes an attempt to explain them. But it can neither create them nor prevent them from recurring. While such history, therefore, teaches us the essential facts that have taken place within two richly endowed centuries, it does not tell us which major facts will form the threads of the next years. It is this unknown factor which makes up the spice of our professional life. We can at least hope that if we conform to reason, to ethics, and to scientific and economic laws for all that is within our scope, each of us will have served this wonderful science that is chemistry to the best of our capacities and in the interests of the greatest number of people. 

Fermi s pile turned out to be a plant which efficiently manufactured a new element in large quantities. This element is plutonium. It is a brand new man-made chemical element which fissons just as easily as U-235. The story of the birth of this synthetic element goes back to a day in May, 1940, when two men using Lawrence s cyclotron at Berkeley, California, bombarded uranium with neutron bullets. The two men were Edwin M. McMillan and Philip H. Abelson. After the bombardment of U-238 they detected traces of a new element, heavier than uranium. This new element, No. 93, was named neptunium by McMillan. It was a very difficult element to study, for its life span was very short. It threw out neutrons immediately and in a split second was no longer neptunium. 

The overall effect of these representations of Watt in statuary and in the story of the kettle was to help to create what I call the mechanical Watt . These images powerfully reinforced the textual generation of the mechanical Watt, a process that I will chart in the next two chapters, and ensured that the chemical Watt remained hidden from view. The mechanical Watt came in two flavours. Some tried to construct Watt as a philosopher-engineer , maintaining that his work was philosophical in nature being based in experimental test and philosophical inquiry. One result of this was a tendency to find in Watt characteristics that anticipated mid-nineteenth centuryphilosophical engineeringof the sort increas-... 

I have two questions the story or the depletion of the ozone has been of great concern in the last years, and I missed in your paper the present judgment on this. You showed differences in ozone reduction from 16 or 18 to 6% or 8%. Does it have any meaning That would be the first question. The other question I have had many discussions with industrialists, politicians etc. and they use the example of ozone and of fluorocarbons as proof that warnings of scientists to do something or to stop the use of certain chemicals are meaningless, and not really justified. In your opinion, the warning of the National Academy of Science has it been justified ... 

Although the public concern about chemical warfare was significant, the story was not completely negative. The dramatic rise in the number of American-born and educated chemists attested to the increasing acceptance of chemistry as an academic subject and career choice. The appetite among publishers for popular science titles such as Morrison s also reflected a growing public interest in science. Man in a Chemical World joined a substantial list of other popular books on chemistry from the era that tried to make clear the importance of chemistry. These included multiple editions of Floyd L. Darrow s The Story of Chemistry (1927, 1930) and Alexander Findlay s A Hundred Years of Chemistry (1937, 1948, 1955, 1965). H.E. Howe s two volume Chemistry in Indus-... 

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