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Пояснения к тексту:

1. it is estimated – зд. доказано

2. naturally occurring waters – природные воды

3. to perish – увядать, гибнуть

4. e.g. например

5. without the agency of light – без помощи света

6. heart disease with failure – сердечная недостаточность

Oxygen

I. Oxygen is widely distributed on the earth in very large quantities. It is an essential constituent of air and water. About one-fourth, 23.2 per cent of the atmosphere by weight, and about one-fifth by volume consists of free

oxygen. Water contains about 88,8 per cent of combined oxygen. Oxygen also forms a material part of rocks since a great number of minerals con­tains a considerable proportion of oxygen. It is estimated¹ that 45 to S3 per cent - nearly one-half the total weight of rocks and eight-ninth of water is combined oxygen.

2. Oxygen, therefore, is the most abundant element, being nearly equal in amount to all the others put together. Naturally occurring waters² hold a small amount of oxygen in solution. Oxygen is an essential constituent of animal and vegetable tissue and fluids. It is absorbed from the atmosphere by animals and plants during respiration and given off by plants when they assimilate carbon dioxide from the air in sunlight. It was established that plants could live in fixed air in which animals perish³ and that plants can restore to fixed air the properties of common air when in sunlight, but not in darkness. The oxygen contains no ozone. Some plants, e.g. bacterium photometricum⁴, can produce oxygen without the agency of light⁵; and chlorophyllous animals give off oxygen in sunlight. It was shown that oxygen is present in the sun; the sun contains dissociated water vapour and consequently free oxygen.

3. There are many methods available for preparing oxygen. We have oxygen around us in great abundance, but it is mixed with nitrogen and it is difficult to separate the two so, as to get the oxygen. The easiest way to get oxygen is by heating something which contains it. One of the simplest examples of this kind is the oxide of mercury, which when heated gives mercury and oxygen. When mercury itself is heated in the air for some time to almost its boiling point it is gradually changed to a red powder, just as lead and tin and zinc are changed to powders when heated in the air. This powder to be a compound of mercury and oxygen decomposes into its elements mercury and oxygen when heated to a high temperature.

4. Various methods of preparing oxygen can be conveniently divided into four classes: 1) Processes dependent on the decomposition of oxides or oxycompounds by heat. The methods of preparing oxygen by heating mercuric oxide or potassium chlorate are typical. Several dioxides (e.g. manganese dioxide, lead dioxide, berium dioxide, etc.) also yield oxygen when heated. 2) Processes dependent on the decomposition of oxides and oxycompounds by chemical means. There is probably no real distinction between thermal and chemical processes as heat may be required to start the reaction in either class, and the thermal processes all involve chemical reactions. 3) Processes in which oxygen is obtained from the atmosphere. 4) Processes dependent upon the electrolysis of water. Nearly all the oxygen is now obtained by the liquid air process.