Text b further development of atomic theory in the 19th century

Pre-reading tasks

1. Have you ever heard about John Dalton, Heinrich Geissler, William Crookes?

2. Can you recollect what they are famous for? What contributions to science did they make?

3. In your opinion, why did scientists of the 19^th century show interest in atomic theory? Explain your viewpoint.

4. Name the achievements of the 19^th century that helped to improve (or modernize) atomic theory.

Reading

Read the text and fulfill the tasks to follow.

Further development of atomic theory in the 19th century

By the early 19th century, atomism had re-entered scientific thought, particularly chemistry, where it strongly influenced British philosopher and mathematician John Dalton (1766-1844). As early as 1803, Dalton, after experimenting with gases, put forward a chemical atomic theory that proposed a more sophisticated model than Democritus or Gassendi. Dalton’s theory, the basis of modern atomic thinking despite some error, was that

Wilheim Conrad Rontgen (1845-1923).R6ntgen's 1895 experiments with the flow of electrical currents through gas of an extremely low pressure resulted in his discovery of a new type of ray that permeated most objects. He called the new phenomenon “X-rays” because their nature was unknown to him. Rontgen’s work inspired the work of French scientist Marie Curie, and led to his receiving the Nobel Prize in Physics in 1921. (Bridgeman Art Library)

atoms combined to form chemical elements. He believed that the atoms in any one element were identical in their masses (an error), but atoms of different elements had different masses. He also believed that atoms could only combine in small, whole-numbered rations (1:1, 2:3, etc.). Dalton based his argument that atoms of different elements had different weights by experimenting with elements to obtain relative particle weight. He was the first scientist to do so. His Table of the Elements, giving them standard symbols, was another great Dalton achievement. Dalton’s laboratory work modernized “atomism”, and inspired later generations of chemists and other scientists to continue to probe atomic theory. One aspect of that theory, unchanged since antiquity, would be the arena where the greatest breakthroughs would come. That was the concept that atoms were unchangeable, and indestructible. Dalton continued the ancient argument, noting, “we might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen.” Future researchers, working with new technology and concepts, would provide the tools to do so.

As the end of the 19th century approached, the Marquis of Salisbury, Robert Cecil, speaking to the British Association for the Advancement of Science in 1894, listed the “unfinished business of science” and posed questions about the atom, namely “whether it is a movement, or a thing, or a vortex, or a point having inertia, whether there is any limit to its divisibility, and if so, how that limit is imposed, whether the long list of elements is final, or whether any of them have any common origin, all these questions remain surrounded by a darkness as profound as ever.”

The first light to illuminate that darkness came from the cathode-ray tube. The cathode-ray tube was the initial child of the development in 1855 of a mercury pump by Heinrich Geissler, which produced vacuum tubes of high quality. Others, such as Sir William Crookes, discovered that when one end of a tube was capped with metal, and a battery was hooked up to them, the airless space inside the tubes glowed, passing from the negative plate - the cathode - to the positive plate, or the anode. When the cathode and anode were placed inside the middle of a tube, and the end of the tube was closed off with glass, the glow would become a beam, or a ray.

Rontgen captured a series of early images made by X-rays on photographic plates, including one of his wife’s hand wearing her ring, which he made on January 25, 1896. Known as roentgenograms, the plates were visual proof of a hitherto invisible phenomenon. (Bridgeman Art Library)

German and British researchers, working with cathode-ray tubes, learned more about the rays between 1858 and 1894. The rays bend when under the influence of a magnet; otherwise they travel in straight lines. They are formed of particles of some sort of matter, which have a charge. In 1874, James Johnstone Stoney, in calculating the charge, suggested that the unit of charge be called an “electrine”. In 1891, he changed the name to “electron”.

Then, in 1895, the German physicist Wilhelm Conrad Rontgen, experimenting with covering tubes with screens to determine the nature of the fluorescent light emanating from them, made an amazing discovery. Even when blocked by cardboard, the tube produced a glow on a nearby screen of chemical-coated black paper. Passing his hand in front of the tube to block the glow, Rontgen discovered that it did not completely block it - and, in the dim light, he could see his bones through the flesh of his hand. A new type of ray - not light - was produced by the cathode-ray tube, and the name Rontgen gave it - the X-ray - stuck.

Comprehension check

1. Consult the text above and complete the following sentences.

1. Atomism reentered scientific ... in the 19^th century.

2. Dalton … a chemical atomic theory.

3. Dalton experimented with elements to obtain relative … weight.

4. Robert Cecil … a number of questions about the atom.

5. The … tube clarified some questions.

6. William Crookes discovered that the space inside the tube … .

7. Under the influence of a magnet rays can … .

8. Stoney introduced the term … .

9. While experimenting with covering tubes with screens Roentgen made an amazing … .

2. Some of the words given in bold type in the text have synonyms and antonyms mentioned there. Find and name them.

3. Some dates (namely, years) are mentioned in the text: 1803, 1855, 1874, 1894, 1895. Can you recollect the events that took place at that time? If necessary, consult the text.

4. Match the names of famous people with the proper information about them. Add some more facts about these people.

John Dalton	suggested to call the unit of charge “electrine”.
Wilhelm Roentgen	developed a mercury pump
James Stoney	discovered that the airless space inside the tube glowed.
Robert Cecil	discovered a new type of ray.
William Crookes	created a table of elements.
Heinrich Geissler	posed questions about the atom

5. Below you will find some theses of Dalton’s atomic theory. Which of them are right and which of them are wrong? Correct the wrong facts (or information).

• Atoms combine to form chemical elements.

• Atoms of any one element are identical in their masses.

• Atoms of different elements have different masses.

• Atoms can only combine in small, whole-numbered rations.

• Atoms are unchangeable and indestructible.

6. Robert Cecil posed a number of questions while speaking to the British Association for the Advancement of Science.

1. Name these questions.

2. Are all these questions solved? If yes, then when and by whom.

7. Comment on the role the cathode-ray tube played in getting information about rays and their properties. (Mention experiments made by Crookes, Stoney, Roentgen).

8. Arrange the following sentences in the logical order to sum up the information given in the text.

1. The cathode-ray tube was used to cast light on some problems.

2. While speaking to the British Association Robert Cecil posed some questions about the atom.

3. Dalton put forward a chemical atomic theory and created his table of elements.

4. William Crookes found out that the glow would become a ray when the end of the tube was closed off with glass and the cathode and the anode were placed inside the tube.

5. He discovered a new type of ray.

6. At the beginning of the 19^th century atomic theory was revived.

7. Roentgen managed to determine the nature of the fluorescent light.

8. Rays consist of particles having charge.

9. In pairs, discuss the information given in the text.

10. You are to prepare a report about the atomic theory of the 19^th century. Use the text given above and add some facts to speak on the point.

TEXT C

X-RAYS

Pre-reading tasks

1. Define the term X-rays.

2. Look at the headline of the text and exchange your opinions on its possible contents.

Reading

Read the text and see what information of this text you managed to predict.

X-RAYS

On 8 November 1895 the German physicist Wilhelm Rontgen was experimenting with a cathode-ray tube. He had left a spare fluorescent screen on another bench, out of the way of his experiment. And yet the discarded screen lit up when he switched on the cathode tube. Rontgen realized that something was coming out of it, some invisible rays that were new to science. He found that they could penetrate all sorts of materials - wood, glass, rubber, aluminium and other metals. And when he put his hand in the beam, he saw a shadow of his bones.

The Rontgen rays were a sensation. Their property of allowing people to see through solid matter seemed like magic black magic to some, thus die invention of lead-lined X-ray ____underwear to repel any prurient applications.

Doctors quickly exploited their new ability to see inside people and experimented with X-rays as a cure for all sorts of illness. But then the dangers of X-rays emerged – burnt and hair loss followed strong exposures, and in 1904 Clarence Dally, an assistant of the American inventor Thomas Edison, died of cancer after being severely burned. X-rays are still used to kill tumours, but the doses are now carefully controlled.

Meanwhile scientists struggled to find out what X-rays actually were. They followed straight lines, like light, but would not bounce off mirrors or bend around obstacles. Could they be waxes in the ether, or bullet-like corpuscles? The question wasn't settled until 1912 when, in an experiment suggested by Max von Laue. a beam of X-rays was shown to be scattered into an intricate diffraction pattern when it passed through a crystal. This proved that they were electromagnetic waves, like light, but of very short wavelength, comparable to the distance between atoms in a crystal. X-ray diffraction became a vital probe of crystals, materials in industry; and the structure of biological molecules such as DNA.

Tasks

1. Based on the information of the text match the dates with the events that took place at that time.

1895	Clarence dally died of cancer being severely burned.
1904	Max von Laue proved experimentally that X-rays were electromagnetic waves of very short wavelength.
1912	Wilhelm Roentgen experimented with a cathode-ray tube.

2. Sum up the main ideas of the text.

3. Write an essay about X-rays: their discovery, nature and applications.

4. Prepare a short report on X-rays applications in different fields