When coal is strongly heated in the absence of air in closed retorts, various useful products are obtained. These are coke, coaltar and coal gas.
Uses of coke Coke is used in the manufacture of steel and in the extraction of many metals. It acts as a fuel and it is a better fuel than coal.
Uses of coal tar The various compounds obtained from coal tar are used as starting materials for manufacturing a large number of substances used in everyday life and in industry like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Naphthalene balls used to repel moths and other insects are also obtained from coaltar.
Uses of coal gas It is used as a fuel in many industries situated near the coal processing plants.

The tremor produces waves on the surface of the earth. These waves are called seismic waves. The waves are recorded by an instrument called the seismograph. This instrument is simply a vibrating rod or a pendulum, which starts vibrating when tremors occur. A pen is attached to the vibrating system that records the seismic waves on a paper. By studying these waves, scientists can construct a complete map of the earthquake.

Outside the house:
(i) Open vehicles, such as motorbikes, tractors, construction machinery, and open cars are not safe.
(ii) Open fields, tall trees, shelters in park, elevated place do not protect us from lightning strokes.
(iii) Carrying an umbrella is also not safe.
(iv) Stay away from poles or other metal objects.
Inside the house:
(i) During a thunderstorm contact with telephone cords, electrical wires and metal pipes should be avoided.
(ii) It is safe to use mobile phone.
(iii) Bathing should be avoided.
(iv) Electrical appliances like computers, TVs etc. should be unplugged. Electrical lights can remain on.

Refining of Petroleum: Petroleum is a dark oily liquid. It has an unpleasant odour. It is a mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax etc. The process of separating the various constituents of petroleum is known as refining. Different constituents of petroleum are LPG, petrol, kerosene, diesel, lubricating oil, paraffin wax, bitumen etc.

Various constituents of petroleum and their uses:
(i) LPG: Fuel for home and industry.
(ii) Petrol: Motor fuel, aviation fuel, solvent for dry cleaning.
(iii) Kerosene: Fuel for stoves, lamps and for jet aircraft.
(iv) Diesel: Fuel for heavy motor vehicles and electric generators.
(v) Lubricating Oil: Lubrication
(vi) Paraffin wax: Ointments, candles, Vaseline etc.
(vii) Bitumen: Paints and road surfacing.

Burning of coal and diesel releases sulphur dioxide gas. It is an extremely suffocating and corrosive gas. Moreover, petrol engines give off gaseous oxides of nitrogen. Oxides of sulphur and nitrogen dissolve in rain water and form acids. Such rain is called acid rain.