Vocabulary:
milling machine– фрезерний верстат, cutting edge – край, що ріже, (to) finish– обробляти начисто, доводити до кінця, circumference – окружність, longitudinal– поздовжній, to rotate– обертати, versatile– вертикальний, flat– плаский, stroke– хід, single-point cutter – одинарний різець, slot– паз, розріз, gear teeth – зуби шестерні,drill– свердлити, to enlarge – збільшувати, fragile– крихкий, abrasive wheel– абразивний круг, bonded– скріплений, simultaneous– одночасний, workshop– майстерня, idle- на холостому ходу, lateral– боковий, grinder – шліфувальний верстат
In a milling machine the cutter (фреза) is a circular device with a series of cutting edges on its circumference. The workpiece is mounted (fastened) on a table that controls the feed against the cutter. The table has three possible movements: longitudinal, horizontal, and vertical; in some cases it can also rotate. Milling machines are the most versatile of all machine tools. Flat or contoured surfaces (фасона поверхня) may be machined with excellent finish and accuracy. Angles, slots, gear teeth and cuts can be made by using various shapes of cutters.
Drilling and Boring Machines
To drill a hole usually hole-making machine-tools are used. They can drill a hole according to some specification, they can enlarge it, or they can cut threads for a screw or to create a smooth hole.
Drilling machines (сведлильнийверстат) are different in size and function, from portable drills to radial drilling machines, multispindle units, automatic production machines, and deep-hole-drilling machines.Boring (розточка) is a process that enlarges holes previously drilled, usually with a rotating single-point cutter held on a boring bar and fed against a stationary workpiece.
Shapers and Planers
The shaper (поперечно-стругальнийверстат) is used mainly to produce different flat surfaces. The tool slides against the stationary workpiece and cuts on one stroke, returns to its starting position, and then cuts on the next stroke after a slight lateral displacement. In general, the shaper can make any surface having straight-line elements. It uses only one cutting-tool and is relatively slow, because the return stroke is idle. That is why the shaper is seldom found on a mass production line. It is, however, valuable for tool production and for workshops where flexibility is important and relative slowness is unimportant.
The planer (поздовжньо-стругальнийверстат) is the largest of the reciprocating machine tools. It differs from the shaper, which moves a tool past a fixed workpiece because the planer moves the workpiece to expose a new section to the tool. Like the shaper, the planer is intended to produce vertical, horizontal, or diagonal cuts. It is also possible to mount several tools at one time in any or all tool holders of a planer to execute multiple simultaneous cuts.
Grinders
Grinders (шліфувальнийверстат) remove metal by a rotating abrasive wheel. The wheel is composed of many small grains of abrasive, bonded together, with each grain acting as a miniature cutting tool. The process gives very smooth and accurate finishes. Only a small amount of material is removed at each pass of the wheel, so grinding machines require fine wheel regulation. The pressure of the wheel against the workpiece is usually very light, so that grinding can be carried out on fragile materials that cannot be machined by other conventional devices.
Ex. 12. Answer the questions to text B:
What is the shape of a cutter in a milling machine?
What moves in a milling machine, a table or a cutter?
What possible movementsdoes the table of a milling machine have?
What kind of surfaces and shapes may be machined by a milling machine?
What can we use a drilling machine for?
What kinds of drilling machines exist?
What is rotated while boring, a cutter or a workpiece?
Describe the work of a shaper (planer).
What must be done to execute multiple simultaneous cuts on a planer?
What is the working tool in a grinder?
Can we obtain a very smooth surface after grinding and why?
Can we grind fragile materials and why?
Ex. 13. Translate into English:
1. Токарський верстат все ще залишається найважливішим верстатом.2. Всі сучасні токарні верстати обладнані електроприводами. 3. Рух інструменту контролюється з високою точністю. 4. Електропривод дозволяє обробляти заготовки на різних швидкостях.
Ex. 14. Analyze the following sentences and translate them:
1. They suppose this method to be time-consuming and difficult. 2. The new method is supposed to be very interesting. 3. It is supposed that this new method can be widely used.4. They found this machine to have been built at our plant. 5. This new device was found at our experimental shop. 6. They appeared quite unexpectedly. 7. They appeared to be wrong. 8. The students appeared to have finished their work beforehand. 9. The text proved to be very difficult. 10. It was proved that he was right. 11. They proved this method to have been useful.
Ex. 15. Find the sentences with the Objective Infinitive Constructions, translate all the sentences:
1. Helium, argon, neon, radon are known to be inertgases. 2. The scientists knew these gases to be inert. 3. Thechemists found the existence of inert gases to have been scarcely suspected until the discovery of argon. 4. Helium, the lightest of the gases, is considered to have the properties, which are very important. 5. A very few compounds of theinert gases appeared to have been reported at that time. 6. They found the atom of helium to contain only two electrons of the first energy level. 7. Radon was found to be the heaviest of the inert gases. 8. Radon as have been stated by some scientists is known to be the direct disintegration product of radium. 9. This gas is to be found in the earth.10. They believe the use of this element to result in manydiscoveries. 11. This element is believed to be widely used.
Ex. 16. Analyze the following pairs of sentences, translate them:
I. A number of new nuclear photochemical methods is known to be widely used.
Everybody knows a number of new nuclear photochemical methods to be widely used.
II. The simplest imaginable way to accelerate a molecule into the electrovolt range is supposed to be mechanical. They supposed the simplest imaginable way to accelerate a molecule into the electrovolt range to be mechanical.
III. The work on the energy dependence of the reactions between ionized molecules was found to have been done with the help of modified mass spectrometers.
They found the work on the energy dependence of the reactions between ionized molecules to have been done with the help of modified mass spectrometers.
Ex. 17. Translate the following sentences, mind the Infinitive Constructions:
1. Thousands of years ago stars were believed to governthe fate of men. 2. Scientists are known to agree that our universe is fundamentally dependent on two factors, one of which proves to be matter, the other energy. 3. The scientist found the atom to have, first of all a nucleus; the nucleus was found to be composed of the protons and neutrons.4.Of all the available building materials, rock and stoneare known to be traditionally associated with permanence. 5. The organic materials with the notable exception of wood appeared to be largely a development of the twentieth century. 6. We know metals to be extracted from natural ores, which of course are also ceramic materials. 7. The metalsturn out not to be as hard as the ceramic materials, but ceramic materials have been stated to be very brittle. 8. Although neither hydrogen nor helium proved to be now commercially produced from air, it is appropriate to mentionthat neither liquid hydrogen nor liquid helium can be transported in the type of equipment used for liquid oxygen, nitrogen, and argon. 9. As the field of chemical engineering developed, physical operations have been found to be convenient to classify into a number of "Unit Operations", which could be separately studied and investigated.
Unit 16
Text A. The Microbiological Production of Industrial Chemicals Text B. Pollution Grammar:Revision |
Text A
THE MICROBIOLOGICAL PRODUCTION OF INDUSTRIAL CHEMICALS
The synthetic capabilities of microorganisms are not confined to food, drink and pharmaceuticals. Microorganisms are known also to produce industrial chemicals that can either serve as or be employed to make solvents, lubricants, extractants, adhesives, plastics, surface coatings, explosives, etc. Often an organic substance with industrial applcations can be made either biologically or by chemical synthesis, the decision to make it one way or the other being essentially an economic one. A major consideration proves to be the cost of the raw materials. In microbiological fermentation the chief raw material has been found to be thegrowth substrate, it usually being starch. In chemical synthesis the principal raw material has been found to be petroleum or a derivative of it. The efficiency of the process must be taken into account. Another factor to be taken into account is the cost of recovering the product from the fermentation medium. One must also weigh the potential value ofby-products, and the cost of disposing wastes.Microorganisms are known to produce some 200 substances of commercial value, only a few of them being currently made by biological methods in industry, they include ethanol, n-butanol, acetone, acetic acid, amino acidsand enzymes. Scientists consider microorganisms to havea larger role in many industries. With the new genetic methods the microbiologists and chemists are able to replace an existing pathway with a new one. To put it another way, they can construct organisms that have new characteristics and capabilities. Thus, microbiological fermentation in conjunction with the new techniques could contribute significantly to the production of three broad classes of industrial chemicals: aliphatic organic compounds, amino acids, and enzymes.
Enzymes can catalyze both the making and the braking of chemical bonds. Each enzyme is stated to act only on a particular substrate molecule.
Commercially produced enzymes are playing an increasing role in medical diagnosis.
Microorganisms have been studied thoroughly but still much is to be studied.
Ex. 1. Translate the following words and state the suffixes of nouns:
Discovery, variety, various, constitution, productivity, useful, usefulness, vary, consideration, considerable, distribution, important, importance.
Ex. 2. Translate the following constructions:
Having examined the substance, they . . .
They having investigated the substance, the analyst
His investigating these phenomena resulted in . . .
The scientists having done new discoveries, it was . . .
The examination of this mixture being carried out, they . . .
Ex. 3. Analyse the "ing"-forms and translate the sentences:
1. Copper being a good electrical conductor, they usedit in their experiment. 2. Like all soluble aluminium salts, the sulphate is readily hydrolyzed, yielding both aluminium"hydroxide" and a solution which is acidic. 3. As a result of one reaction decreasing in velocity while the other is increasing, a point presently is reached at which the two reactions are proceeding at the same rate and the products of each reaction are being used up at the same rate at which they are formed. 4. The temperature increased, the heatbeing evolved. 5. The solution obtained, we could begin carrying out our experiment. 6. A steel containing some metallic element other than iron and carbon is generally known as "special steel". 7. Large amounts of hydrogen are used in industry in converting oils into solid fats. 8. Manynuclear reactions result from interacting of nuclei and neutrons. 9. Using only very small quantities of the substance, she succeeded in obtaining a considerable amount of information about the chemical properties of the elements. 10. Mercury may be purified by washing it with dilute nitric acid.11. They were using this substance in their experiment several times. 12. While examining the properties of this metal pay attention to its melting point. 13. Upon being heated the oxide changes into the red modification. 14. Being lower than hydrogen in the activity, mercury does not displace hydrogen from solutions of the acids. 15. His having created this new machine soon became known to everybody.16. All nitrates decompose upon being heated and hence serve well as dry oxidizing agents.work must be very accurate.
Ex. 4. Find the sentences in which "that", "those" substitute nouns:
1. Before this discovery, it had been supposed that specific composition and formula could represent only one substance. 2. The density of ice proved to be lower than that of the liquid. 3. The volume of steam has been found to be many times that of liquid water. 4. The energy liberated by the complete disintegration of lg of radium intolead is equivalent to that obtained by the combustion ofmore than half a ton of coal. 5. The range is greater for atoms of even atomic numbers than for those of odd numbers.6. This review reveals that all atomic nuclei are believed to contain protons. 7. The neutron cannot be accelerated byuse of the electric machine, but slow-moving ones appear to be more effective than are those of greater speed. 8. Germanium resembles silicon in that it forms several unstable hydrides. 9. Vessels made of platinum-rhodium alloy areeven less susceptible to loss of weight on heating than are those made of platinum alone. 10. They had to use those vessels, which were less susceptible to loss of weight on heating. 11. We make use of the heat energy that is evolved when wood and coal change into gases and ashes to heat our homes and to provide power for industry. 12. Chemical research today is proceeding more rapidly than that before. 13. Theseare a number of substances that absorb moisture.
Ex. 5. Translate the following sentences paying attention to the words in bold type:
1. Changes involving identical materials prove to produce the same results. 2.The results of our investigation are surely to be correct. 3. This new element is known to have been discovered as a result of great experimental activity. 4. No solution will result from mixing two immiscible liquids. 5. It is now believed that complex ions result from the sharing of electron pairs by the simple ion and the ions or molecules, which become attached to it. 6. Great results in different fields of science have been achieved recently. 7. Disintegration will continue through a number of expulsions until a stable nucleus results.
Ex. 6. Translate the following sentences, mind the Passive Infinitive:
1. This research work can be carried on in our new laboratory. 2. The production of consumer goods must be greatlyincreased next year. 3. This canal is known to have beenbuilt last year. 4. We know the new buildings of our Institute to be built in two years. 5. They expect this investigation to be carried out by young engineers. 6. This problem should be solved by the end of this month.
Ex. 7. Analyse the following pairs of sentences, translate the sentences:
I. Having constructed a new powerful chemical accelerator, they could start their work. A new powerful accelerator having been constructed, they started their work.
II. The electric computer simplifying greatly the calculations, it is much easier now to find out all the properties of new substances.
The electronic computer simplifying the calculations has been used in our laboratory.
III. A metal and non-metal combining transfer of electrons occurs with the formation of an ionic crystal. A metal combining with a non-metal was investigated in our laboratory.
Ex. 8. Translate the following nouns:
Rapidity, solubility, direction, absence, simplicity, investigator, investigation, variety, definition, involvement, difficulty, relation, length, strength.
Ex. 9. Translate the following sentences, mind the verb forms:
1. Having examined the properties, they could continue their work. 2 Examining the static properties of molecules helped them in their work. 3. The properties examined by the electronic computer were very important. 4. The computer employed in our laboratory, was very good. 5. The computer having been employed, they could finish their work in time. 6. Employing the computer, they could make very important calculations.
Ex. 10. Translate the following sentences, mind the tensesof the Predicate:
1. For nearly a century the scientists working with food have been trying to understand more fully the role of microorganisms in fermentation. 2. The rising cost of petroleum has made the product less competitive. 3. The introduction of microbiology into the pharmaceutical industry has brought about a transformation profound enough to be called a revolution. 4. They have been working at the problem involved since 2012, but still much is to be done. 5. Recently, it has become widely accepted to use this technique in determining the weight of some substances. 6. This view of conservation laws has been radically changed by the development of the modern theories of elementary-particle interraction.7. He had been carrying out the experiment for two hours when I came into the laboratory. 8. They have been working out the new procedure for at least a month, they will have to begin their experiments. 9. A great number of foreign scientists have visited our laboratory as it is considered to be the best one in our Research Institute. 10. A lot of workers have been attending these courses to get acquainted with the new methods of producing some products from different chemicals. 11. Our chemists have solved a great number of urgent problems in the field of environmentalprotection lately. 12. I was asked how long I had been working at that plant. 13. The new apparatus had already been installed in our shop by the end of November. 14. The work hasn't been finished yet, we have to continue experimenting.
Ex. 11. Translate the following sentences into English, mind the use ofthe tenses:
1. Він відвідує лекції з хімії з вересня. 2. Він відвідав кілька лекцій з вересня. 3. В минулому роцівін відвідав кілька лекцій по загальній хімії. 4. До грудня він провів цілу серію експериментів. 5. Коли я почав роботу, він вже закінчив експерименти. 6. Він вивчає фізичну хімію вже три роки. 7. Нещодавно ми відвідали виставку «ХІМІЯ-2016». Вона справила на нас дуже велике враження. 8. В минулому році ми відвідали ряд хімічних заводів. 9. Коли я увійшов у лабораторію, він вже проводив дослід протягом години. 10. Коли я увійшов до зали, доповідач говорив про розвиток хімії полімерів в нашій країні.
Ex. 12. Translate the following sentences paying attention to the Subjunctive Mood and Adverbial Clauses of Condition:
1. Free silicon might be expected to be produced both inaboratory and in industry. 2. This question couldn't be answered with certainty if you didn't carry out a number of investigations. 3. If this research had been done earlier, the role of this element would have been clear. 4. This element could be predicted if you knew the properties of the other elements. 5. Were all the properties known, it would be much easier to use this element. 6. Nitrogen itself is known to be inactive. If the atmosphere contained much more than the normal amount of it, the chemical activityof the oxygen, an active ingredient of air would be too much retarded. 7. Had the laboratory been repaired in time, we should have finished our research much earlier. 8. It wouldbe interesting to find out all the properties of these elements. It is necessary that all the properties of these elements be investigated before we start experiments.
Ex. 13. Translate into English using Subjective and Objective Infinitive Constructions:
1. Відомо, що останнім часом фармацевтичнапромисловість значно розвинулася. 2. Було встановлено, що етанол є одним з найбільш важливихорганічних хімікатів у цій промисловості. 3. Мизнаємо, що ця стаття присвячена розвитку мікробіології в нашій країні. 4. Виявилося, що вартість виробництвацих речовин дуже велика. 5. Відомо, що наукові співробітники нашого інституту провели серію експериментів, використовуючи органічний розчинник бутанол, і отримали гарні результати. 6. Цей метод, мабуть, старий і не дає гарних результатів 7. Вони знали,що досліди були закінчені і результати були задовільними. 8. Виявлено, що з промислових кислот оцтова кислота є найважливішою. 9. Цей розчинник, мабуть, не може бути використаний в нашій галузі. 8. Виявлено, що з промислових кислот – оцтова кислота є найважливішою. 9. Цей розчинник, мабуть, не може бути використаний в нашій галузі.
Ex. 14. Translate the following sentences paying attention to the meanings of the word "provide":
1. The steel may be provided with the desired degree ofhardness depending on the temperature to which it is reheated.2.To provide the laboratory with necessary equipment much money should be spent. 3. Our new laboratory is provided with gas and running water. 4. The materials provided by nature can no longer satisfy the rapidly developing technology. 5. The mass spectrum can be used to provide unique information concerning the molecular structure of some unknown compounds. 6. This type of information provided by this technique is new. 7. They will apply these new methods provided they are effective enough.
Text B
POLLUTION
Pollution is known to be of great concern to both science, industry and to humanity as a whole.
There has always been pollution, even when man was not present. When man appeared upon earth, he added much to the pollution. As the population of man on earth increased, pollution increased too, it being increased in three waysthrough the numbers of persons, through the industrial activity, and through man's use of devices such as automobiles that cause pollution. One of the most important tasks tobe solved is air pollution. All countries are currently spending great sums of money on environmental protection.
The study of pollution could be divided into three main parts: pollution of the air, of water and of the land mass. To study this problem is very important for man.
Air Pollution
Every smoking chimney turns out to be a source of air pollution. Home furnaces tended to; burn soft coal incompletely, thus adding unburned carbon particles to the air.
The use of natural gas or oil that have a negligible mineral content is of great help in reducing pollution, but hasthe disadvantage of rapidly consuming materials, whichcould better be conserved for future generation as raw materials for the manufacture, for example, chemicals and plastics.
It has been found that some chemical processes, such asthe manufacture of lime, Portland cement, steel, tend togive off much dust.
Lead, bromide and chloride emitted from the exhaustof automobiles which burn lead-containing gasoline produce a lead-chloride-bromide aerosol which is consideredto be a common air contaminant in urban areas, it beintoxic to people. The chief atmospheric gaseous pollutants originating from the earth's surface appeared to be oxidesof sulphur, oxides of nitrogen, incompletely burned hydrocarbons, and carbon monoxide.
These gases are known to react with energy from sunlight to produce photochemical smog. Smog not only can be highly irritating to eyes and lungs, but it can also cause extensive damage to vegetation? There are many problems to be solved concerning the pollution of air.
Water Pollution
Some cities simply run their raw sewage directly intonearby natural waters. This is one of the worst types of water pollution. Another type of pollution of sea and ocean water is petroleum oil, it taking place in connection with off-shore drilling operations. It should be also noted that unfortunately there is yet no satisfactory method of overcoming the effects of oil spills, although many methods have been tried.
Earth Pollution
In addition to air and water, the solid part of the earthis also in danger from pollution. Solid wastes include such things as: metal cans, glass bottles, plastic containers, ashes from the combustion of coal and wood, and radioactive isotopes. The problems created by pollution are very difficult, but fortunately, great progress is being made in their solution.
The atmosphere over cities is the object of constant care and attention on the part of the government. Each year steps are taken to improve the protection of the atmosphere from harmful factory pollution.
Hundreds of new devices trap and neutralize the harmful substances contained in discharged gases go into service. As a result, in more than 70 per cent of cities where theair monitored, discharges of dust, sulphur gases andhydrogen sulphide were either stabilized or reduced altogether, harmful industrial pollution of the air of cities and industrial centres having been greatly diminished through out the country.
Extensive measures are being taken to set up reservations and carry through biotechnical measures for the protection and reproduction of species of animals, birds and valuable fish.
Much money is being spent, but it should be noted that money alone is not enough to protect the environment. The attitude of people is vital and much depends on the people.
There will never be complete success unless human beings are taught to use nature with care.
Ex.15. Translate the following word combinations, mind the Participles II:
The method involved was; the experiment spoken of is;the lecture followed by the experiment took place; the datareferred to must be; the report resented involved somedata; the figures summed up resulted in; the book translated consisted of 2 parts; the work done helped greatly;the ore found contained; the solution used is to be heated.
Ex.16. Translate the following sentences, mind the Infinitives:
1. The copper to be used must be pure. 2. The metal isto be used in our experiment. 3. To use this solution wehave to heat it. 4. To use these figures is to complete thiswork. 5. The method seems to be useful in this work. 6. Thework done proves to be of great importance. 7. They found this substance to melt at a low temperature. 8. The application of zinc is known to be important in heavy industry.9. Zinc is known to be a silvery white metal. 10. This metal appears to be readily dissolved by most mineral acids.
Ex.17. Translate the following sentences:
The problem to be solved deals with environmental protection. 2. Some chemical processes to be consideredwere of great importance. 3. Raw materials to be used for manufacture of some chemicals can be obtained in this region. 4. The discovery to be made in the field of nuclearphysics was of great value. 5. The substances to be purified should be carefully treated. 6. The lecture to be followed by the experiment was devoted to pollution. 7. The figures to be referred to should be arranged in the table.
Ex.18. Translate the sentences with Conditionals:
1. Would you like to come with us? 2. Would you be so kind as to tell me how to get to the Red Square? 3. Could you tell me the way to the main building of the University? 4. Would you mind giving me your dictionary for a minute? 5. Would you be kind enough to pass me the text-book? 6. I'd like to thank you for your help. 7. He'd like to meet you.
1. You are the only person she would listen to. 2. The material in that book is very much out of date. The book must have been written a long time ago. 3. He speaks English well. He must have lived in the United States for a long time. 4. You could have done it in a different way. 5. It's strange he is not here. However, he might have forgotten all about it. Or he might have come while I was out. 6. For long journeys in private cars one could use automatic guidance systems. 7. One laser beam could carry all the radio, TV and telephone messages simultaneously.
1. Mary wishes she could drive a car. 2.1 wish that, for just a day, I were President of the United States. 3.1 wish I had not spent so much money yesterday. 4. I wish when a boy I had studied French instead of English. 5. John wishes he had been a mechanical engineer. 6. I wish I had a car. 7. I wish you had mentioned this fact to me before.
1. If he were better educated, he would get the job. 2. Were I you, I should speak to him about it. 3. I would have called you if I had had your telephone number. 4. Had she felt better, she would have gone with them. 5. If you watched a laser operate, you might be surprised at the simplicity of a device capable of such power. 6. «If I had had a chance to live my life again, I should have tried to combine the study of the history of art, philosophy and science. » «But then you wouldn't be good at either.» «No, you are probably right, I'd be a dilettante. »
1. K. Onnes found that it was necessary that a mercury wire be cooled to –265°C for electrical resistivity to disappear. 2. Tsiolkovsky proposed that liquid propellants should be used for space travel. 3. Recently it has been improbable that superconductivity should appear at an unbelievable temperature of 98 К in a special ceramic material. 4. The great speeds and high resistance of air demand that new hyperliners be built without windows. 5. It is essential that a superconductor should be a solid material and it is necessary that it should be cooled to –273 °C. 6. It was natural for the ancient Greeks to suppose that the stars, planets, the sun and the moon move round the Earth in space. 7. It is possible that a compound should become a superconductor even if the chemical elements constituting it are not. 8. Copernicus suggested that the Sun and not the Earth should be at the centre of everything.
ADDITIONAL TEXTS
Ozone: Properties, Toxicity, and Applications
Words and Word-Combinations to Be Memorized:
silent discharge – тихий розряд; require – вимагати; environment – навколишнє середовище; pass through a vessel – проходити через посудину ; bond – зв’язок; rat – щур; undergo – піддаватися |
Common methods for ozone generation are ultraviolet radiation, silent electric arc discharge and electrolysis. The ultraviolet radiation technique is used only when relatively low concentrations are required, e.g. for environmental study. The electrolysis of water is not widely used because of its low efficiency. So far, the action of silent electric discharge on oxygen is the most common method for the production of ozone. It gives a yield of 6% by weight of ozone.
When high purity or quantity of ozone is desired, it is possible to use liquid ozone. The ozone-oxygen mixture from one of the above methods is passed through a vessel at liquid oxygen temperature (–183°C). Because of the large difference in the vapour pressure of ozone and oxygen, oxygen is pumped off from the mixture whereas ozone is liquefied. Liquid ozone is then vaporized from the concentrated system for further use.
Ozone is a colourless gas with characteristic odour, which is detectable by nose and provides a warning of toxic exposure. The ozone molecule is non-linear with a bond angle of 116°. In contrast to oxygen, gaseous ozone is diamagnetic and possesses four resonance structures with (III) and (IV) accounting for its electrophilic nature.
Mechanistic studies of the biological effect of ozone are of particular interest. Vitamin E prolongs the life of rats exposed to ozone. This is based on the observation that the vitamin E-depleted group undergoes a more significant change than the vitamin E-supplemented group in the fatty acid composition of total lung lipid. Therefore, vitamin E, the biological antioxidant, provides protection from ozone toxicity.
Ozone is a particularly destructive substance to rubber and other elastomers.
Liquid-Vapour Equilibrium
Words and Word-Combinations to Be Memorized:
Attractive, bind, constant, dependence, initial, magnitude, note, primarily, proportional, situation, spontaneous, substantial, it was not until... that, not until, vessel, zero, evaporate, entirely, overcome the forces, leave the liquid, the magnitude of the energy, range from... to, substantial, overcome the binding forces, be proportional to, remain the same, start immediately, the dependence is worth considering, become equal to, per unit time, consequently, at a fixed temperature, remain unchanged, opposing processes |
A liquid of relatively low boiling temperature, when placed in a container open to the atmosphere, will eventually evaporate entirely. Remembering that molecules in the liquid are "bound" by attractive forces to their neighbours, we might ask why some are able to overcome these forces and leave the liquid spontaneously. The answer lies in a considerationof the possible magnitudes of molecular kinetic energies, for these, as we have already mentioned, range from very low to very high values, and are distributed according to the Maxwell-Boltzmann Law. Therefore, even if the average potential energy which binds the molecules to the liquid is substantial, there are always some molecules which have enough kinetic energy to overcome the binding forces and enter the vapour. According to the Maxwell-Boltzmann Law, the fraction of the molecules which have kinetic energies greater than some minimum values, the value required for the molecules to leave the liquid, is proportional to the Boltzmann factor. Therefore, the temperature remaining constant, the fraction of liquid molecules with enough kinetic energy to evaporate remains the same, and evaporation continues. The vessel being open to the atmosphere, vapour molecules are swept away, and evaporation continues until no liquid is left.
Now, let us analyse what happens when a liquid is placed in a closed evacuated container. Immediately, the liquid starts to evaporate at a rate which is primarily determined by the fraction of molecules which have enough kinetic energy to overcome attractive forces and leave the surface. Initially, the rate of condensation is zero, there being no molecules in the vapour. As long as the temperature stays constant, evaporation continues at a constant rate, and the number of molecules in the vapour phase increases. Consequently, the rate of condensation starts to increase, for as the pressure of the vapour grows, the number of gas molecules which collide with and reenter the liquid surface also increases.
The time dependence of the evaporation and condensation rates is worth considering. While growing, the condensation rate eventually becomes equal to the rate of evaporation. At this time, the number of molecules which enter and which leave the vapour per unit time is the same, and, consequently, the pressure of the vapour stops increasing and remains constant. If the system is left undisturbed at a fixed temperature, evaporation and condensation continue at equal rates, and the pressure of the vapour remains unchanged. This, then, is a situation of equilibrium between the two phases. Note particularly that at equilibrium, evaporation and condensation do not stop, but at the constancy of the equilibrium vapour pressure is a consequence of these opposing processes proceeding atequalrates. Thus, we say that phase equilibrium isdynamic in nature.
Insulator Turns into Superconductor
Having used ultrahigh pressures and critically low temperatures, our scientists have managed to effect such a unique transformation as converting a sulphur insulator into a superconductor.
Superconductivity, at which a conductor completely lacks resistance to electric current, was discovered more than 80 years ago. This phenomenon occurs at temperatures around -273°C.
Present-day electronic, electrotechnical apparatuses, instruments and machines have been developed, operating on superconductors under
conditions of low temperatures. Among them are radio-receiving devices for detecting weak signals arriving from the depths of outer space, highly efficient powerful, and yet small, current generators, transformers and cables.
The equipment that uses superconductors is expensive and is not available for users at large. That is why scientists are looking for materials which would become superconducting at a temperature of, for example, liquid hydrogen, which is –252°C, or liquid nitrogen, which is –196°C. Sulphur has been quite unexpectedly found among the superconducting materials.
The main unit of this installation is a high-pressure chamber. It contains two anvils of synthetic polycrystallinc diamond, "carbonado" or black diamond. The surface of one anvil is flat, whereas the other one is shaped as a cone. When compressed, the anvil point develops a pressure of half a million atmospheres! Under such conditions sulphur converts to a "metallic" formation. "Metallic sulphur", cooled by liquid helium, acquires superconducting properties at a temperature of –269°C.
Experiments are being continued and have so far yielded interesting results. Sulphur has increased the temperature of coversion into a superconducting material to –242°C.
Up to nowr a champion in high temperature superconductivity has been a niobium-to-germanium compound. Its conversion temperature into a superconducting state was –250°C. Now the leadership has passed over to sulphur.
Some Facts about Quantum Mechanics
The first half of the nineteenth century was an intensely active period for discovery of electric and magnetic effects, best exemplified by the brilliant work of M. Faraday and the complete unification of many diverse experimental observations by Maxwell.
Not only did Maxwell's prediction of the electromagnetic nature of light unify the fields of optics and electricityand magnetism, but its subsequent experimental demonstration by Hertz in 1887 appeared to be a final blow to theold (corpuscular) theory of light. The early twentieth century saw the birth of the theory of relativity and of quantum mechanics.
The first, due to Einstein alone, completely altered the ideas of space and time, it being an extension of classical physics to the region of high velocities and astronomical distances.
Quantum mechanics on the other hand, was developed over several decades by many scientists and it being an extension of classical physics to subatomic, atomic, and mole relativity theory has played a profound role in our everyday life through the concept of the equivalence of mass and energy and its manifestation through nuclear energy, it has not yet played an important role in the field of chemistry.
Quantum mechanics, however, in dealing with the atomic and molecular region has played a very important role in chemistry.
Many scientists were interested in quantum mechanics and worked hard at this problem, one of them being Bohr.
It should be noted that the significant occurrence on the road to the development of quantum mechanics was Bohr's theory of the structure of the hydrogen atom.
According to the nuclear model of the atom, the hydrogen atom can be pictured as a central rather massive nucleus with one electron. Because the nucleus is so much more massive than the electron, we can consider the nucleus to be fixed and the electron to be revolving about it.
The force holding the electron in a circular orbit is supplied by the coulombic force of attraction between the proton and the electron. It was Bohr's great contribution to make these assumptions. Bohr's theory was found to give a very true picture of the hydrogen atom.
A great number of scientists continued working at this problem and achieved great success.