3.4. Reading comprehension. Read the text Availability, Properties and Classification of Metals and for questions 1­–5 (after the text) choose the best answers from a–d.

Vocabulary

availability n	—	доступность, наличие
smelt v	—	плавить (руду)
gangue n	—	пустая порода
extract v	—	извлекать
either … or conj	—	или … или
distinguish v	—	характеризовать, различать
lustre n	—	блеск, глянец
dull a	—	матовый, тусклый
weak a	—	непрочный, слабый
thus adv	—	так, таким образом
on the other hand	—	с другой стороны
tarnish v	—	тускнеть
ferrous metal	—	черный металл
non-ferrous metal	—	цветной металл

Availability, properties and classification of metals

Metals are the most abundant of materials to supply man’s present needs. The availability of metals does not depend on the amount present in the Earth, but on the ease with which their ores can be obtained and smelted. Although 1/12 of the Earth’s crust by weight consists of aluminium, many compounds of this metal are unsuitable as ores.

The majority of useful metallic ores contain the metal combined with oxygen, sulphur, or other elements. Some ores are comparatively rich, others contain large amounts of gangue. This term is applied to the constituents of the ore other than the mineral containing the metal to be extracted. Extracting metals from their ores and modifying them for use is the main task of metallurgy.

The word “metal” is used in two ways. In the narrow and more precise meaning, a metal is a chemical element having metallic properties. In the broader, more colloquial usage, it signifies any material, either element or alloy, which has metallic properties.

In the narrow sense, the word “metal” has been defined as an element which is hard, heavy, distinguished by a “metallic lustre”, malleable, ductile, strong and usually a good conductor of heat and electricity. It is certainly not a precise definition, because an element can be soft, light, dull, brittle or weak and still be a metal.

Carbon and silicon are fairly good conductors of heat and electricity and thus resemble the metals. On the other hand, they have no considerable strength nor ductility and in this respect they resemble the non-metals. If we cut a piece of lead with a knife, the fresh surface shows a beautiful lustre. However, the surface will tarnish very fast on exposure to the air.

According to the commercial classification all the metals are divided into two groups: ferrous and non-ferrous metals. Iron and its alloys are classed as ferrous metals. It is customary to assume that manganese and chromium used as additions to iron are ferrous metals. Ferrous metals make up about 95% of metallic products. The other metals are non-ferrous.

Note

on/under exposure to the air – под воздействием воздуха (на воздухе)

1. The availability of metals is connected with

a) how much of them there are in the Earth.

b) the fact that it is not difficult to get them and smelt from their ores.

c) the fact that metals are the most widespread materials on earth.

d) the fact that metals are in pure state in nature.

2. Which is true according to the text?

a) Metals are always hard, heavy, malleable, ductile, strong, good conductors of heat and electricity, have a metallic lustre.

b) All metals are combined with oxygen, sulphur or some other elements.

c) Iron and its alloys are not considered to be ferrous metals.

d) 5% of metallic products are not ferrous.

3. They in bold type (line 23) refers to

a) carbon and silicon. b) heat and electricity.

c) the metals. d) good conductors.

4. Which of the statements is not true according to the text?

a) Ores can’t be used directly in metallurgy.

b) Metals are elements with a variety of properties.

c) Carbon and silicon are metals.

d) Metals can be grouped into ferrous and non-ferrous classes.

5. Any metal

a) can be cut with a knife.

b) is strong.

c) is extracted from its ore which is easy to obtain and smelt.

d) can be referred to one of the two groups: ferrous and non-ferrous metals.