Read the text and correct the statements that follow.

Metals

One basis of classification of the elements groups them into metals and non-metals. It is now 2,000 years since Julius Caesar was stabbed in a small auditorium known as Pompey's Curia and his body cremated in the Roman Forum. Since that time, many changes have taken place, but many things have remained the same. Steel is still the basic material of armaments, although, it is not used in the manufacture of shields and short swords. Gold, silver, and copper are, as 2,000 years ago, the coinage metals. Bronze is still used for objects intended to resist the corrosive action of the atmosphere.

Knowledge of the metals, of course, has increased, greatly since Caesar's day. The Roman world knew, at least, copper, lead, gold, silver, tin, iron, mercury, and zinc (in a copper alloy). To this list, the twentieth-century's man in the street might add aluminium, magnesium, nickel, chromium, cobalt, tungsten, molybdenum, uranium, and one or two others.

The first metals which were used by primitive man were those that are found free in nature to a comparatively large extent. These are gold, silver, and copper. Tin entered the metal picture when someone discovered, probably accidentally, that if it was mixed with copper the resulting substance was harder. So there came into being the alloy that we call bronze, a material which was so important in the ancient world that its name is given to one of the cultural stages in human development. The Bronze Age began in Egypt around 3,000 BC and in Europe some 500 or 1,000 years later.

Since almost no iron exists free in nature, it undoubtedly came into general use somewhat later than those just mentioned. As soon as methods were developed for separating iron from its ores in reasonably large quantities and at fairly low cost, it ceased to be classed as a precious material and began its career as the world's most valuable metal from the standpoint of actual use.

Metals are mostly solids at ordinary temperature and have comparatively high melting points with the exception of mercury. They are for the most part good conductors of heat and electricity. They can be drawn into fine wires and hammered into thin sheets, characteristics that are called ductility and malleability, respectively. An ounce of gold can be drawn into a wire almost 50 miles long or hammered into a sheet that has an area of between 175 and 200 square feet.

From the point of tonnage produced and used, iron is the world's most common metal, followed in turn by copper, zinc, lead and aluminium.

1. Bronze is still the basic material of armaments, although, it is not used in the manufacture of shields and short swords.

2. The Roman world knew, at least, copper, lead, gold, silver, tin, iron, mercury, aluminium and zinc.

3. Non-metals are mostly solids at ordinary temperature and have comparatively high melting points.

4. The Bronze Age began in Europe around 3,000 BC and in Egypt some 500 or 1,000 years later.

5. One basis of classification of the elements groups them into solids and liquids.

6. Gold, silver, and bronze are, as 2,000 years ago, the coinage metals.

7. Iron is still used for objects intended to resist the corrosive action of the atmosphere.

Date: 2015-12-11; view: 1114