7. Read and translate the text mercury in the environment

Mercury is known to be a rare element. The element is found in trace amounts throughout the lithosphere (rocks and soil), the hydrosphere, the atmosphere and the biosphere (in tissues of plants and animals).

In the rocks and soil mercury is found to be measured in fractions of one part per million. In the hydrosphere (the seas and fresh waters) it occurs only in parts per billion. In the atmosphere mercury is present both as vapour and in the form of particles. It should be noted, however, that under natural conditions the amount of mercury in the atmosphere is so small that extremely sensitive methods are required for detecting and measuring it.

The situation is somewhat different in the biosphere. Plants and animals tend to concentrate mercury. For example, it has been found some marine algae to contain a con­centration of mercury more than 100 times higher than that in the seawater in which they live.

Mercury today is used on a substantial scale in chemical industries, it being used in the manufacture of paints and paper as well as in agriculture. The world production of mercury has been found to amount to about 10,000 tons per year.

In agriculture mercury in the form of corrosive sublimate (HgCl₂) can be used for disinfecting seeds. The chlorides of mercury are employed in protecting a number of vegetable crops.

Due to such large-scale uses a considerable amount of mercury waste is likely to flow into the air, the soil, the streams, rivers, lakes. One might ask whether all these may present a threat to health.

In order to answer this question it is necessary to exam­ine the forms in which mercury occurs. Liquid mercury itself is not toxic to man, but mercury vapour, however, can be injurious. The soluble inorganic salts of mercury have long been known to be toxic.

So, knowing properties and forms of mercury it is possible to use it.

Mercury being very important, it is useful to continue investigating its properties very closely.

Properties of Mercury

Mercury is unusual in that it is the only metal which is stable in the liquid state at about 20°C. It has a bright silvery luster, shows little tendency to tarnish at ordinary temperature, it being a good conductor of both heat and electricity.

Because of its uniform expansion over a wide range of temperature, it is well adapted to use in thermometers, and due to its high density, low coefficient of expansion, and slight vapour pressure at ordinary temperature it is well suited for using in the liquid type barometer.

Despite having high boiling point, mercury does show a small vapour pressure even at ordinary temperatures.

Being raised to a temperature above its boiling point, mercury vapour readily conducts electricity at the same time emitting radiation, it being rich in ultraviolet rays.

Notes on the Text:

1. one part per million – одна часть на миллион

2. on a substantial scale – в больших масштабах

3. to amount to – составлять; равняться (чему-л.); достигать (чего-л.)

8. Answer the following questions:

1. Where can mercury be found? 2. What methods are required to detect the presence of mercury in the atmosphere? 3. Where is mercury used? 4. In what form is mercury used in agriculture? 5. What is mercury used for in agriculture? 6. Why is mercury considered to be unusual metal? 7. What properties of mercury do you know? 8. Why can mercury be used in thermometers and barometers? 9. When does mer­cury conduct electricity?