STORY OF COAL
You may have seen coal or heard about it (Fig. 5.1). It is as hard as stone and is black in colour.
Figure 5.1: Coal
Coal is one of the fuels used to cook food. Earlier, it was used in railway engines to produce steam to run the engine. It is also used in thermal power plants to produce electricity. Coal is also used as a fuel in various industries.
About 300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like flooding, these forests got buried under the soil. As more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation. Since it was formed from the remains of vegetation, coal is also called a fossil fuel. A coal mine is shown in Fig. 5.2.
Figure 5.2: A coal mine
When heated in air, coal burns and produces mainly carbon dioxide gas. Coal is processed in industry to get some useful products such as coke, coal tar and coal gas.
Source: This topic is taken from NCERT TEXTBOOK
COKE
It is a tough, porous and black substance. It is an almost pure form of carbon. Coke is used in the manufacture of steel and in the extraction of many metals.
Source: This topic is taken from NCERT TEXTBOOK
COAL TAR
It is a black, thick liquid (Fig. 5.3) with an unpleasant smell. It is a mixture of about 200 substances. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Interestingly, naphthalene balls used to repel moths and other insects are also obtained from coal tar.
Figure 5.3: Coal tar
These days, bitumen, a petroleum product, is used in place of coal-tar for metalling the roads.
Source: This topic is taken from NCERT TEXTBOOK
COAL GAS
Coal gas is obtained during the processing of coal to get coke. It is used as a fuel in many industries situated near the coal processing plants. Coal gas was used for street lighting for the first time in London in 1810 and in New York around 1820. Now a days, it is used as a source of heat rather than light.
Source: This topic is taken from NCERT TEXTBOOK