2018-02-13
1227
Learn the new vocabulary:
| rare | рідкісний, рідкий |
| trace amounts | незначна кількість |
| soil | грунт, земля |
| under natural conditions | у природних умовах |
| extremely sensitive | дуже обережний, ніжний |
| to tend (to) | мати тенденцію |
| algae | водорості |
| corrosive sublimate | сулема |
| seed | зерно |
| due (to) | завдяки, через |
| wastes | відходи |
| to present a threat (to) | загрожувати |
| injurious | шкідливий |
| soluble inorganic salts | розчинні неорганічні солі |
1. Read and translate the text:
Mercury is known to be a rare metal. 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 water) it occurs only in parts per million. In the atmosphere mercury is present both as vapor and in the form of particles.
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 that some marine algae contain a concentration of mercury more than 100 times higher than that in the seawater in which they live.
Mercury 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 sublimates (HgCl2) can be used for disinfecting seeds. The chlorides of mercury are employed in protecting vegetable crops.
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Due to such large-scale uses a considerable amount of mercury wastes 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 vapor, however, can be injurious. It has long been known that the soluble inorganic salts are 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.
2. Divide the text into logical parts, entitle them.
