THE ELECTRICAL PROPERTIES OF MATERIALS

The electrical conductivity of material was first demonstrated in 1792 by the English experimenter Gray. His demonstrating this phenomenon made his name well known at that time.

It was he who touched a charged glass rod to the end of a moistened cord and discovered that the cord transmitted the electricity to a distance of about 1,000 feet.

Today the exploration of the electrical properties of materials is disclosing much more interesting phenomena. We know of many new experiments having been carried out in this field. All these have turned out to be of fundamental significance in the understanding of matter, as well as of great technological importance.

To begin with, the wide range of electrical conductivities exhibited by materials is itself a striking fact. The difference in electrical conductivity between the most conductive substances (for example, copper and silver) and the most resistive (polystyrene) amounts to 23 orders of magnitude.

If we want to understand the extent of this spread, we should compare it with extremes in the scales of distance. One might note, for instance, that the ruler needed to measure the size of the universe, is only some 23 orders of magnitude larger, than the mile ruler that measures distance on the earth.

Evidently then, the electrical conductivity (or rather its inverse resistivity, the quantity used in statements of Ohm's Law) is one of the most widely varying of all physical quantities. The individual materials begin showing great variability in resistivity according to the conditions of temperature, pressure and the mixture of component substances.

If a minute trace of gallium or arsenic (one part per billion) were added to pure germanium, its conductivity would be increased by two orders of magnitude (nearly l,000 fold) and would rather make it suitable for using in transistors. A tiny further addition of the impurity could increase the conductivity 100,000fold, converting germanium to a conductor.

Similarly silicon and metal oxides such as nickel and titanium dioxide are lowered in resistivity by introducing of appropriate impurities. Indeed nickel oxide, which is an insulator in the pure state, is reduced in resistivity by 13 orders of magnitude by adding only one per cent o£ helium.

Thus a semiconductor can be made a conductor by heating it to a high temperature or it can be made an insulator by cooling it to a low temperature.

In contrast, the resistivity of a pure metal is much less increased by heating and reduced by cooling.

In some cases the change is very abrupt. For example above 150 kelvin vanadium is a semiconductor, when it is cooled its resistivity suddenly jumps and it becomes a good insulator. Some semiconductors and insulators are extremely sensitive to light. Thus upon illuminating, their conductivitymay be several orders of magnitude higher than it is in the dark. This phenomenon is called photoconductivity.

1. When was the electrical conductivity of material first demonstrated? 2. What experiment did Gray carry out? 3.What is the most resistive substance? 4. What do the individual materials show? 5. What happens if a minute trace of gallium or arsenic is added to pure germanium? 6. When are nickel oxideand titanium dioxide lowered in resistivity? 7. What changes are produced by changes in temperature? 8. When does vanadium become a good insulator? 9. What phenomenon is called photoconductivity?

1. The electrical (провідність) of different materials was investigated by many scientists. 2. Today (дослідження) of the electrical properties of solids has revealed many interesting phenomena. 3. To understand (значення) of this investigation we must compare it with the previous one. 4. If (найдрібніші) trace of arsenic were added to pure germanium, the conductivity of the latter would increase. 5. Great (зміни) can be produced by increasing temperature. 6. In some (випадках) the change is very abrupt. 7. Some (напівпровідники та ізолятори) are extremely sensitive to light. Can you say what principles (пояснюють) the great differences in conductivity between metals and insulators?

1. In a crystal of copper, in which the atoms are packed together, the electrons spread themselves over the wide range. 2. In contrast to copper, the atoms of the semiconductor germanium turned out to be together, by forming covalentbonds. 3. It is advisable to use a solution whose resistance will be of about the same order of magnitude as the resistances in the previous solution. 4. On account of the resistanceof tin to the action of air and water, it is used to coat othermetals 5. Having finished measuring, you should turn off the light. 6. How can this phenomenon be accounted for? This is a question which in its turn can be solved only by veryexperienced chemists. 7. In order to understand this process oneshould read some papers before starting his work. 8. In eitherof these cases the solubility of lead will be lowered practicallyto zero. 9. On account of its resistance to corrosion, copper iswidely used. 10. Traces of aluminium, which dissolve in solidcopper greatly reduce the electrical conductivity. 11. If this substance is heated and turned red, cupric oxide is formed. 12. If concentrated hydrochloric acid is added to a solution of cupric chloride, the green solution turns brown owingto the formation of the complex anion. 13. Because of uniform expansion over a wide range of temperature, mercury isused in thermometers. 14. As a rule, if the length of a conductor is doubled, the resistance is doubled too.

Suitable, significant, impure, increase, cool, conductor, light, decrease, insulator, insignificant, unsuitable, warm, dark, pure.

It will be interesting to note that an iron wire of the same length as a copper one has a greater resistance. Under the same conditions, the copper wire allows more current flowing than the iron wire. Copper has a greater conductivity. Conductivity means the ability of carrying the current. The unit of conductivity is the siemens or the mho. The unit of resistance is the Ohm.

In 1826 Ohm found a simple correlation between resistance, current and voltage. He also observed that if the voltage remains the same, the greater the resistance, the smaller the current is.

So, it can be stated: the current that flows in a circuit is directly proportioned to the voltage and inversely proportioned to the resistance.

About seventy-nine of the one hundred substances are metals. A metal may be defined as a substance, which has large conductivity of electricity and of heat, has a characteristic luster, called metallic luster, and some other properties. In addition, the electric conductivity increases with decrease in temperature.

The metals themselves and their alloys are of great usefulness to man. The importance of some alloys is due primarily to their hardness and strength. These properties are a consequence of the presence in the metals of very strong bonds between the atoms.

For this reason, it is of great interest to us to understand the nature of the forces holding the metal atoms together in these metals and alloys.

First, we should consider an alloy to be a metallic material containing two or more elements. It may be homogeneous, consisting of a single phase, or heterogeneous, being a mixture of phases.

Liquid air is a mixture of the liquefied gases. It is a milky liquid owing to the presence of solid carbon dioxide and ice. If these solids were removed by filtering, the filtrate would have a pale blue tint.

Liquid air due to its extremely low temperature produces remarkable physical changes.

If a tin or iron vessel were cooled by liquid air, it would become so brittle that it could be crushed with the fingers.Mercury freezes so hard in liquid air that it could be used as a hammer. It could be hardly crushed.

If the liquid air were in a tea kettle standing on a block oi ice, the liquid air would boil vigorously. If the kettle of liquid air were placed over a lighted Bunsen burner, frost and ice would collect on the bottom of the kettle.

Ordinary liquid air is from one half to one fifth liquid oxygen, and therefore it can support combustion.

A red hot rod of steel would have burned brilliantly if it had been placed in the liquid air.

Lately numerous applications of liquid air have been proposed and have been used in all branches of life. For example, it can be used to remove diseased flesh from the wounds. It can be widely used as commercial source of oxygen and nitrogen. Liquid air can be readily manufactured in large quantities at a comparatively low cost, that is why liquid air is made use of both in industry and in everyday life.

Ordinary air contains nearly constant proportions of three elementary substances, viz. nitrogen – 75.4 per cent, oxygen – 23.2 per cent and argon – 1.2 per cent by weight. It also contains small proportions of several inactive gases in some proportions of carbon dioxide, water vapour and lust.

The relative proportion of water vapour in the air could be stated in terms of relative humidity, i. e. the ratio between the concentration of water vapour in the air and the concentration required for equilibrium at the same temperature.

If the relative humidity were low, evaporation would occur rapidly. If the relative humidity were high, evaporation would occur slowly as the air is nearly saturated.

1. What is liquid air? 2. What are the properties of liquid air? 3. What changes can liquid air produce? 4. When does an iron vessel become brittle? 5. What freezes hard in liquid air? 6. What do you know about ordinary liquid air? 7. Where is liquid air applied? 8. What does ordinary air contain? 9. When can evaporation occur rapidly? 10. What would happen if the relative humidity were high?

To use, to produce, due to, to manufacture, quickly, to employ, rapidly, owing to.

Active, to solidify, warm, solid, inactive, the same, cool, to liquefy, different, liquid.

1. In terms of the given formula N₄0 we can say that air is a mixture of nitrogen and oxygen. 2. Water is sometimes cloudy due to the presence of some particles. 3. They can hardly solve the problem without you. 4. We know that ice can freeze hard if the temperature is low. 5. The lecture was attended by nearly all the students. 6. If we work hard, we shall certainly finish our work soon. 7. Air conditioning requires the regulation of both the temperature and humidity. 8. When the air is not in circulation, the layer near the body becomes nearly saturated. 9. The transition point at which a change takes place is described in terms of temperature and pressure.

Ex. 7. Translate the following sentences, state the function of the words in bold type:

1. Both copper and tin melt at a low temperature. 2. The reaction of acids with metal hydroxides is a completed reaction because of the low degree of ionization of water. 3. The only manganic compounds which may be prepared in aqueous solution are those of low solubility. 4. If a highly compressed gas composed of molecules is allowed to expand quickly to low pressure, its molecules overcome the forces of attraction, consequently, the temperature of the gas is lowered. 5. Ceramic products could be characterized by low thermal conductivity. 6. The freezing point lowers in this reaction. 7. The scientist tried to lower the concentration of the absorbed substance in the reaction.

Ex. 8. Find the sentence where the word “change” is a verb. Translate the following sentences:

1. This is well known that changes take place in all the substances. 2. Chemical changes are usually permanent. 2. Chemical changes are usually permanent. 3.The changes that take place during the freezing of a liquid are opposite to those that take place during the melting of the solid. 4. There is little change in the concentration of complex anions so long as the solution is acidic. 5. It has been shown that every chemical change could be accompanied by a definite energy change. 6. The vapour pressure of a liquid is affected by changes in temperature. 7. If you changed the temperature, the reaction would go to completion.

1. (На основі) the kinetic theory, the energy of molecules increases with rise in temperature. 2. When he was a student he (бувало) spend a lot of time in the reading-room of this Institute. 3. Oxygen is also (використовується) to maintain air composition for respiration at high altitudes. 4. I shall finish my work (яктільки) I get good results. 5. They can (ледве) finish their research without his help. 6. (Останнійчас) many new articles dealing with this subject have been published. 7. The heat of combustion of acetylene, (тобто) the number of calories evolved per mole, is large. 8. The most extensive industrial (використання) of oxygen is in the production of high temperatures in oxygen-gas flames. 9. Ozone decomposes slowly at room temperature but rapidly and (легко) at 250°. 10. The reactions of ozone are of the same variety (как) those of oxygen. 11. This (термін) can be (використаний) by us. 12. (Ще) in the 16th century the scientists knew this reaction. 13. (Зміна) in temperature results in the (зміни) of solubility. 14. The velocity of a reaction is (змінюється) by (змінюванням) in conditions. 15. The ventilation of a room requires (як) a sufficient supply of fresh air (такі) the circulation of the air. 16. Air conditioning requires the regulation of (як) the temperature (такі) the humidity.

1. If there were no dust, the air would become supersaturated with water. 2. If air is cooled sufficiently, it can be converted into a liquid. 3. If the liquid air were allowed to evaporate, different components would predominate in the fractions obtained at different temperatures. 4. If the atmosphere continued to be of uniform density, we should find that it is 5 miles deep. 5. Were a quantity of silver chloride placed in a quantity of water, silver and chloride ions would begin to leave the surface. 6. Had water been added to the mixture, more alcohol and acid would have been formed. 7. Had not chemistry made possible the production of fundamental materials, radio and TV would have been unknown.

1. This article does not deal with organic chemistry. I shall not translate it.
2. I have no time. I shall not go to the library. 3. He does not feel well. He does not attend lectures.

1. If she were in the laboratory, she... 2. Provided they prepared for their examination better, they... 3. Were he free, he... 4. Unless he came in time, he...

1. If he had read that book, he... 2. If she had not been ill, she... 3. Provided they had come earlier, they... 4. If he had been in her place, he...

1. If liquid boiled, nitrogen (to escape) from the solution more rapidly than oxygen, as its boiling point is lower than that of oxygen. 2. Provided a liquid had evaporated into a closed space, its gaseous molecules (to leave) the liquid surface. 3. Unless he helps me, I (to be able) to finish this work in time. 4. If we did not know the nature of radioactive elements, it (to be difficult) to deal with them. 5. If they had studied the activity of uranium, they (to understand) that phenomenon better. 6. If this molecule (to be) decomposed, we should obtain atoms. 7. Provided zinc were heated with sulphuric acid, the metal (to replace) hydrogen. 8. If someone weighed, say 80 kilograms at the North Pole, he (to weigh) less at the equator. 9. If sulphur burns in air or oxygen, the main product (to be) sulphur dioxide.

Ex. 14. Supply the appropriate forms of the verb instead of the Infinitives in brackets:

1. The reaction will not take place, unless they (to add) a catalyst. 2. Provided you wanted to obtain pure nitrogen, you (to pass) gaseous ammonia over heated copper oxide. 3. If at ordinary temperatures molecules of a gas exhibit no attraction, Joule-Thompson effect (to be) not effective.4. If a liquid had been cooled gradually, it (to reach) a temperature at which crystals of the solid form (to begin), to appear. 5. Were this laboratory equipped well, it (to be) much easier to work in it. 6. Were the oxygen in the air reduced below a certain percentage, it (not to support) combustion. 7. Unless iron is heated red-hot, it (not to absorb) any carbon. 8. If you took a little salt and examined the grains, you (to see) that most of them are perfect cubes. 9. Provided there were no air, the piece of paper and the piece of iron (to fall) together. 10. If one or more of the reacting substances were a weak electrolyte, the reaction (to involve) the dissociation of such substances into ions. 11. If the concentration of one of the ions involved is greater than the equivalent proportion, the concentration of the other (to be) less.

1. Physical changes, continue as long as the exciting cause exists. 2. As the evaporation continues, the temperature of the water grajiual|y drops. 3. A solution containing no excess of the acm or the basic hydroxide is known as a neutral solution. 4. A few of these oxides also react with water as noted in the previous book. 5. As little as one part of heavy water in 100,000 parts of water may be detected. 6. Solvents, as we shall see later, sometimes decompose a compound into its constituents. 7. We shall start our work as soon as a number of experiments is carried out. 8. As a continuation of our work on the relation between the strength and the chemical composition of glass we carried out a number of experiments. 9. As it is estimated, nearly half of the sun by weight is hydrogen. 10. The laboratory is the place where experiments as well as scientific researches of great significance are carried out. 11. As a rule, acids are not reactive unless they are in solution. 12. These books were published as early as at the end of the last century. 13. Aluminium as well as copper are the best conductors of electricity. 14. The existence of neutrons was discovered as late as in 1932. 15. Mechanical processes of separation include distillation as well as freezing. 16. This experiment is as interesting as the previous one.

Note: use – використовувати, вживати, use – використання, вживання, користь, used to— матизвичку (звичайно) робитищо-неб.

make use of— використовувати, використати, вживати

1. The analytical balances are used for accurate weighing of samples. 2. It was known long ago that oil could be used as a raw material. 3. The combination of atoms and the arrangement of atoms in a molecule used to be regarded as the special field of the chemist. 4. One of the most important uses of electricity is the production of heat. 5. The electric lamp widely used for the generation of light depends on the heating property of electricity. 6. For a number of reasons mercury is used in barometers. 7. Atomic energy has many peaceful uses. 8. Commercial and home refrigerators make use of Joule-Thompson effect. 9. Aside from its uses in research laboratories radium is used chiefly in the treatment of some diseases.

chip – стружка, content – склад, topermit – дозволяти, tungsten – вольфрам, tip – наконечник, truing – правка, наводка, заточка, die – матриця, штамп, coarse – грубий, to pierce – проколювати, to punch – пробивати отвір, hardened – загартований, nut – гайка

Dies are tools used for the shaping of solid materials, especially those employed in the pressworking of cold metals.

In press work, dies are used in pairs. The smaller die, or punch, fits inside the larger die, called the matrix or, simply, the die. The metal to be formed, usually a sheet, is placed over the matrix on the press. The punch is mounted on the press and moves down by hydraulic or mechanical force.

A number of different forms of dies are employed for different operations. The simplest are piercing dies (пробивний штамп), used for punching holes. Bending and folding dies (загибний) are designed to make single or compound bends. A combination die is designed to perform more than one of the above operations in one stroke of the press. A progressive die (штамп послідовної дії) permits successive forming operations with the same die.

In coining, metal is forced to flow into two matching dies, each of which bears an engraved design (гравійований малюнок).

In the manufacture of wire, a drawplate (волочильна дошка) is usually employed. This tool is a metal plate containing a number of holes, successively less in diameter and known as wire dies. A piece of metal is pulled through the largest die to make a coarse wire. This wire is then drawn through the smaller hole, and then the next, until the wire is reduced to the desired measurement. Wiredrawing dies are made from extremely hard materials, such as tungsten carbide or diamonds.

For cutting threads on bolts or on the outside of pipes, a thread-cutting die (різьбонарізнаплашка) is used. It is usually made of hardened steel in the form of a round plate with a hole in the centre. The hole has a thread. To cut an outside thread, the die is lubricated with oil and simply screwed onto an unthreaded bolt or piece of pipe, the same way a nut is screwed onto a bolt. The corresponding tool for cutting an inside thread, such as that inside a nut, is called a tap (мітчик).

1. Усі різці і фрези повинні мати гостру ріжучу кромку.

2. Під час різання ріжучий інструмент і деталь мають високу температуру і повинні охолоджуватися.

3. Вуглецеві сталі часто використовуються для виготовлення різців тому, що вони недорогі.

4. Швидкорізальної сталі містять вольфрам, хром і ванадій.

5. Алмази використовуються для різання абразивних матеріалів і чистової обробки поверхні твердих матеріалів.

6. Для різних операцій використовують різні штампи.

7. Волочильні дошки для дроту робляться з дуже твердих матеріалів,

8. Різьбонарізні плашки і мітчики використовуються для нарізкирізьблення зовні і всередині.

1. If we look around, we can see that electricity is serving us in one way or another. 2. If I were free, I should help you with pleasure. 3. If we had tested this material, we should have used it in our work. 4. If ordinary gases are greatly compressed, they become liquids. 5. If supercomputers had not been used for thermodynamic calculations, designers would have spent all their lives on computations. 6. If you think that a computer never makes mistakes, you are wrong. 7. If extreme temperatures generated by atmospheric friction were not so high, a hypersonic craft would not require complicated cooling measures. 8. If we had been told about the lecture on reliability in spacecraft production, we should have come by all means. 9. Superconductivity can be obtained in some materials if the temperature is very low and close to absolute zero.

1. If you (to know) English well, you will be able to read books in the original. 2. If I get this book, I (to be) very happy. 3. You (to become) much stronger if you did your morning exercises regularly. 4. If she went to work in France, she (to learn) French very quickly. 5. If he (to see) her, he would have spoken to her. 6. I (to help) them if I had been at home. 7. You (to write) the testwork well if you have learnt grammar. 8. If she (to ask) me yesterday, I should have told her about it. 9. If we had not been present at the lecture, we (not to understand) the new approach to the solution of the problem.

1. I would work much better if.... 2. Life would be much simpler if.... 3. Use every opportunity to practice English if.... 4. I would have started to study English earlier, if.... 5. I would have had more opportunities, if....

If he had known about the lecture, he would have come. Had he known about the lecture, he would have come.

1. If it were possible, we should begin this work at once. 2. If he had had all the necessary books, he would have made his report in time. 3. If the books had been available in our library, we could have done this work much earlier. 4. If there were no computers, space flights would be impossible. 5. If drivers were more attentive while driving, there would be less accidents on the road.

1. Had he used new materials, the device would have been more reliable. 2. Were electric motors used, cars would not pollute the air, would be practically noiseless and very easy to control. 3. Had they applied the new method, the result would have been much better. 4. Were the design of cars improved, the fuel consumption would be greatly reduced. 5. Had a less explosive gas been used in dirigibles at the beginning of the century, they would have been in operation since that time. 6. Were it possible to learn how birds find their way, people would use the principle to develop a navigation system for aviation.

First, there were some elements still missing from the Periodic Table. The fact was they were practically missing from nature, too.

Scientists had to make these elements themselves. To make such elements meant first of all to carry on great experimental work. Many scientists worked hard at this problem. In 1919, Ernest Rutherford was the first to change nitrogen to oxygen by bombarding nitrogen atoms with alpha-particles.

To alter an element artificially is to add or subtract particles in its nucleus. The first completely new man-made isotope was created by Rutherford's method, its creators being Irene Curie and her husband Frederic Joliot. To do that they had to bombard aluminium with alpha-particles.This attack transformed some of the aluminium atoms in to a highly radioactive substance. This substance was a new kind of phosphorus, its atomic weight being 30, instead of natural phosphorus 31.

It was no wonder that phosphorus 30 did not occur in nature, its half-life being only two and a half minutes. Thus, the Joliot-Curies were the first to produce "artificial radioactivity".

The era of artificial transmutation began with the building of the first "atom-smasher", i.e. the cyclotron. By means of cyclotron and energetic particle-accelerators developed later it became possible to open up the nucleus of any atom. It became possible to add particles to it, and even to create new ones.

The first element produced in this way was the missing number 43, it being named "technetium" meaning "artificial". The aim of the scientists was to discover other elements.

In 1939, a new element was found. It behaved like an alkali-metal, therefore it was to be 87 the missing number of the alkali-metal family. It was called "francium". It was detected in nature. Later that element was produced artificially by an accelerator, and only then did chemists obtain enoughof it. For that reason francium is to be considered as a man-made element.

Later scientists discovered traces of an element in neutron-bombarded uranium. They called it "neptunium". Radioactive neptunium gave rise to another element – number 94.

In 1955, chemists could produce a few atoms of element 101, which was named "mendelevium" in honour of D.I. Mendeleyev. The isolation of element number 102 occurred in 1963, it being named "nobelium", as part of the work was done at the Nobel Institute in Stockholm. The next element to be produced was 103. It was named "lawrencium" for E. Lawrence, the inventor of the cyclotron. Then the task was to discover the next element. It was 104. It was named "kurchatovium" in honour of the great scientist I. V. Kurchatov, who worked in the field of nuclear physics. He conducted a great deal of research in the field of nuclear physics. The scientists of the whole world continue their research in the field of artificial elements.

1. Why did it become possible to make elements artificially? 2. What problem did many scientists work at? 3. Whatdoes it mean to alter an element artificially? 4. What element was produced by Irene Curie and Frederic Joliot? 5. How did they get this element? 6. What is cyclotron usedfor? 7. What element was produced by means of cyclotron? 8. What element was found in 1955? 9. Why was element number 104 named "kurchatovium"? 10. How many elementsin the Periodic Table are known now?

Ex. 3. Find the English equivalents of the following wordsand word combinations in the text:

штучні елементи; на честь; період напіврозпаду;стало можливим; викликати; відкритий; він поводився подібнолужному металу.

1. (За допомогою) of a new cyclotron it became possibleto open up the nucleus of any atom. 2. The new device wascreated (замість) an old one. 3. The element produced (таким чином) was named ''technetium". 4. The element behaved (подібно) an alkali-metal. 5. Radioactive neptunium (привів) to another element – number 94. 6. The isolation of element number 102 (мало місце) in 1963. 7. (He дивно) that many new discoveries have taken place recently.8. (Нарешті) they succeeded in creating a new type of machine. 9. This element was named (на честь) of this famousscientist. 10. It was (особливо) difficult to distinguish this substance. 11.It was (майже) impossible to create a new type of machine at our plant.

1. The research-workers of our Institute had to carry on hard work to find out all the missing properties of this substance. 2. He has to work hard this term as he missed manylectures. 3. It was hardly possible to distinguish the properties of this substance at a glance, therefore a powerfulmicroscope had to be used. 4. They worked hard and their hard work resulted in new interesting discoveries. 5. If youstudied hard, you would hardly fail at the examination. 6. She will hardly come as she is very busy.7.The molecules of even the hardest steels can be separated by enormous distances compared to the size of the molecules.

Ex.8. Remember the meanings of the following words, translate the sentences:

1.Artificial graphite surpasses practically natural graphite in purity and particularly in homogeneity. 2. Acetylene is a very important starting material particularly for preparation of a number of synthetic products. 3. Observations were made partially in order to determine if there was any relation between these two elements. 4. Polystyrene is a thermoplastic, which can be used in laboratories particularly for windows. 5. Practically there is no great difference between these two substances, the former one being more soluble in water. 6. I know him to be particularly interested in this problem. 7. No phase separation was shown practically on cooling crucible just below the temperature of the liquid. 8. It is very difficult to define the shape of these glasses particularly since it appears impossible to quench these glasses to homogeneous materials.

To accelerate, to have made, to attack, to use, to havedetermined, to take, to suppose.

Study and remember the following chart, mind the functions of the Infinitive:

1. Many ores, which are to be found in our region will be used in industry. 2. The report, which will be made by thisscientist deals with very important problems in the fieldof atoms. 3. The solution, which is to be filtered was pouredinto a flask. 4. The article which is to be translated is published in our journal. 5. The experiment, which will be carried out, will help us in our investigation.

1. Dalton was the first who deduced scientifically theatomic theory from experimental data. 2. She was the last who learned the news. 3. Alpha radiation was the first that was studied in detail at that time. 4. He was the third who translated the article so well. 5. This student was the last who left the laboratory.

Ex. 11. Translate the sentences. Pay attention to the functions of the Infinitives:

1. Chemical reactions that change the concentration of hydrogen ions to become the same as in pure water are called neutralization reactions. 2. Ammonium ions interact withwater to form hydronium ions in equilibrium with molecular ammonia. 3. No special regulation of concentration is required to effect a separation between the chlorides of theseions.4.The purpose of these experiments was to observe properties of the element involved. 5. The aim of these research-workers is to find out the required element. 6. As a result of many experiments involving combining weights, chemists have been able to determine the relative weightsof different elements. 7. The substance to be extracted should be more soluble in the extracting solvent than in the initial solution. 8. Some of the metals are not active enough to react with water at ordinary temperature. 9. To establish the molecular weight of oxygen means to find the number of atoms in the oxygen molecule. 10. The apparatus to be used in our work was constructed in our laboratory. 11.Whereis the mixture to be heated?12. E. Rutherford was the first to change nitrogen to oxygen by bombarding nitrogen atoms with alpha particles. 13. To determine the relative weights of different elements we were to use the relative system of atomic weights. 14. A slight addition of pressure at this temperature should cause liquefaction to take place, but beyond this temperature no amount of pressure would enable the gravitational attraction to exceed the energy of motion.15. In order to liquefy a gas at a temperature below its critical temperature, it is practically necessary only to compress the gas.

pressurewelding – зварювання під тиском,riveting – клепка, клепання, flux – флюс, fusible – плавкий, toshield – затуляти, захищати, tip – кінчик, край,filler – наповнювач,heatwelding –зварювання нагріванням, bolting – скріплення болтами, arcwelding – електродугове зварювання, flame – полум’я,rod – прут, стержень, coated – покритий, simultaneously – одночасно

Welding is a process when metal parts are joined together by the application of heat, pressure, or a combination of both. The processes of welding can be divided into two main groups:

• heat welding, when the weld is achieved by heat. Heat welding is the most common welding process used today.

Nowadays welding is used instead of bolting and riveting in the construction of many types of structures, including bridges, buildings, and ships. It is also a basic process in the manufacture of machinery and in the motor and aircraft industries. It is necessary almost in all productions where metals are used.

The welding process depends greatly on the properties of the metals, the purpose of their application and the available equipment. Welding processes are classified according to the sources of heat and pressure used: gas welding, arc welding, and resistance welding. Other joining processes are laser welding, and electron-beam welding.

Gas welding is a non-pressure process using heat from a gas flame. The flame is applied directly to the metal edges to be joined and simultaneously to a filler metal in the form of wire or rod, called the welding rod, which is melted to the joint. Gas welding has the advantage of using equipment that is portable and does not require an electric power source. The surfaces to be welded and the welding rod are coated with flux, a fusible material that shields the material from air, which would result in a defective weld.

Arc-welding is the most important welding process for joining steels. It requires a continuous supply of either direct or alternating electrical current. This current is used to create an electric arc, which generates enough heat to melt metal and create a weld.

Arc welding has several advantages over other welding methods. Arc welding is faster because the concentration of heat is high. Also, fluxes are not necessary in certain methods of arc welding. The most widely used arc-welding processes are shielded metal arc, gas-tungsten arc, gas-metal arc, and submerged arc.

In resistance welding, heat is obtained from the resistance of metal to the flow of an electric current. Electrodes are clamped on each side of the parts to be welded, the parts are subjected to great pressure, and a heavy current is applied for a short period of time. The point where the two metals touch creates resistance to the flow of current. This resistance causes heat, which melts the metals and creates the weld. Resistance welding is widely employed in many fields of sheet metal or wire manufacturing and is often used for welds made by automatic or semi-automatic machines especially in automobile industry.

The metals are those, which have the bright luster and other characteristics which are usually associated with such substances as iron, silver, zinc and tin, while the non-metals are those substances which do not have characteristics
of metals.

By far the greater number of elements are known to be metals, since the transition elements are all metals. The elements could be still further subdivided into five groups, three of which being metallic and two of which being non-metallic.

Light-scattering phenomena – явища розсіювання світла

How does laser light differ from ordinary light? In brief, it is much more intense, directional, monochromatic and сoherent. We know the light emitted by an ordinary source such as candle or an incandescent lamp to consist of uncoordinated waves of many different lengths, that is, it is incoherent and more or less white.

The scientists found the waves of laser light to be coordinated in space and time and to have nearly the same length.This coherence and chromatic purity and also intensity oflaser light result from the fact that in a laser excited atoms are stimulated to radiate light before they have had time to do so spontaneously and independently. The directionality of laser light arises from the geometry of the laser.

These properties of laser light suggest many uses for it both in technology and in physics. The scientists considerlaser light to be different from ordinary light even when it merely illuminates a surface. The surface looks grainy and sparkles.

By means of some instruments it has become possibleto examine materials and physical phenomena in new ways. Among the most interesting applications of the laser the probing of materials by the study of their scattering of light should be mentioned.

The laser is being applied to probe the internal structure and behaviour of molecules by examining the light-scattering phenomena. Many investigators are working at the development of coherent light sources, those ones whose wave-length can be changed.

Laser light is applied in many fields such as medicine, biology, industry and so on. We can say scientists made laser light serve man.

The scientists found the energy density of the image formed by a lense in a laser beam to be used to heat, melt oreven vaporize small areas of any material. Laser is also used to pierce holes in diamond.

Soon laser is to be used to cut a wide range of materials including wood and paper.

The scientists work hard to use laser in all fields of scienceand life. They expect laser to be widely used almost everywhere. It will be used for the well-being of people.

1. What is the difference between laser light and ordinary light? 2. What did the scientists find out about the waves of laser light? 3. What do the properties of laser light suggest? 4. Why did it become possible to examine somematerials in a new way? 5. Which is the most interesting application of laser light well known to everybody? 6. Where else can laser be applied? 7. Why is the discovery of laser light so important? 8. What are many scientists working at?

Ex. 2. Form words of the same root using the prefixes "in-", "im-", "dis-","un-":

Direct, different, dependent, visible, possible, advantage, pure, coordinated, definite.

Ex. 3. Translate the following sentences paying attention to the meanings of "much":

1. This acid is much stronger than that you used before. 2. This reaction depends much on the surrounding air. 3. There is much iron in this deposit. 4. He works much in the laboratory. 5. He likes his work very much. 6. They had to workwith the solution containing as much as 95% of organic solvents.7.There is much glassware in our laboratory.

1. Light weight metals are required in the manufacture of aircraft equipment. 2. Silver halides darken when ex posed to white light. 3. The production of light is the secondary phenomenon in those cases in which the energy of activation is large. 4. Aluminium is a light metal, which exhibits a silvery luster. 5. The first electric power station built in this region lighted the houses and industrial enterprises. 6. The amount of light radiated by an atomic bombis so great that one could hardly imagine it. 7. The laboratory is lighted very badly, there should be much more light. 8. All light metals are widely used in all the branches of industry.

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