My Science School

Petrol is one of the most useful products in the world. Cars, scooters, aeroplanes and various other automobiles - all consume it as their fuel. It is also the source of light and other forms of energies.

Petrol is obtained from petroleum - a viscous dark-coloured liquid found inside the earth. The word ‘petroleum’ is derived from the two Latin words ‘Petra’ and ‘oleum’ meaning rock and oil respectively. It is found usually in pools beneath the earth’s surface. Petroleum is sometimes called ‘black gold’ because it is highly useful for us. Do you know how this oil is formed inside the earth?

Millions of years ago, plants and animals got buried in earth’s interior due to geological upheavals. Intense pressure and heat inside the earth converted the decomposed plants and animals into petroleum. Man discovered its massive stocks in the sea-bed too.

The crude oil is drawn out of petroleum wells. This consists of petrol, naphtha, kerosene, diesel, pitch etc. It is brought to refineries for purification and extraction of these products. The crude oil is heated in very big cylindrical vessels. The various constituents of the oil are separated as different fractions at different temperatures and taken out through separate pipes. This process is known as fractional distillation. The various other products obtained from petroleum include plastics, paints, drugs, explosives, cleaning fluids and detergents.

Scientists have succeeded in synthesizing petrol by some artificial techniques also but petrol prepared in this way is costlier.

It is found in many countries but mainly in Gulf countries, USA and Russia. In India, it is mainly found in Assam and Bombay. 

Marble is a kind of lime stone which is available in many colours. White marble has been in use for construction of buildings since ancient times. The people of Greece and Egypt used this stone for construction of temples. The Taj Mahal of Agra is also made from the white marble. It is unaffected by heat, cold, rains etc.

                 Marble is found in nature in the form of rocks. You may not be aware as to how these rocks are formed? These rocks are formed from lime-stones. The tremendous heat and pressure beneath the earth’s surface converts lime-stone into marble rocks. If you analyze the chemical composition of marble, you will find that it is mostly calcium carbonate. Some varieties of marble contain ninety-nine per cent calcium carbonate. Marble acquires a variety of colours due to the presence of some salts of aluminium and magnesium in it. Pure marble is snow white.

                  It is cut into big pieces from the rocks by machines. These big pieces are brought to workshop where they are cut into convenient desired sizes. Marble obtained from rocks is initially coarse. To smoothen its surface, it is polished with the help of special machines. After this it is ready for use. Italy has some of the vast and well known marble quarries in the world. About one lakh tonnes of marble is obtained in Italy every year. The longest marble quarry of USA is located in Vermont.

                  Because of its beauty, it has always been a favourite material for sculpture, architecture and many other purposes. Famous sculptors, like Michelangelo and Leonardo da Vinci used marble for many of their works.

                  In India, Bheraghat in Jabalpur (M.P.) is such a place where rocks of marble are found in abundance. Rocks of marble are also found in Rajasthan. Marble of Makrana is very famous.

 

                Antibiotics are special kind of medicines which inhibit the growth of or destroy Bactria and some other disease producing micro-organisms. They help our body to fight against diseases hence they are used in the treatment of many diseases.

                The word ‘antibiotics’ is derived from ‘antibiosis’. ‘Anti’ means ‘against’ and ‘biosis’ means ‘life’. Antibiotics act only against certain types of micro-organisms like bacteria. In fact, ‘antibiotics’ are chemical substances derived from the bodies of micro-organisms such as bacteria, moulds or some plants.

            The antibiotic era began around 1928 with the discovery of a species of Penicillium by Sir Alexander Flemming. Flemming named the substance Penicillin. This antibiotic was effective in the treatments of pneumonia, cough, inflammation of throat, boils, sores etc. Streptomycin is another antibiotic which is used in the treatment of Tuberculosis. In addition to these, Ampicillin, Tetracyclin, Chloromycetin and many other antibiotics are used for curing various diseases. In fact there are more than 80 known antibiotics. Some antibiotics are effective against just some micro-organism while some other are effective against a large range of micro-organisms. Those which cover a large range are called broad-spectrum antibiotics. When an antibiotic is brought into the body either by injection or capsules, it kills the disease spreading micro-organism.

                   Do you know how antibiotics are made? Most of the antibiotics are made from bacteria and fungi. Scientists have not been really able to know the complete mechanism by which antibiotics kill the germs of diseases. Some scientists think that antibiotics prevent oxygen from reaching the germs of diseases and in the absence of oxygen they die. Some other scientists say, antibiotics prevent the germs from taking food from the body and they die for want of food. Whatever may be the mechanism of the action of antibiotics, it is an established fact that these medicines have proved very useful for mankind. Every year millions of people in the world suffering from various diseases are saved by these medicines. In 1930, 20% to 85% of total deaths in America were due to pneumonia. In 1960, this figure came down to 5%. Similarly, the deaths due to typhoid have come down from 10% to 2%. Infectious diseases can also be checked with their help. They are also useful in preventing diseases like throat infection, rheumatic fever, venereal diseases etc.

                   They have their adverse effects also, such as reaction of the body to them, rashes and other symptoms may develop or they may cause other diseases. An extreme reaction may even lead to death. Sometimes, they are ineffective on the germs of the diseases.

 

  Pure pearls are very precious. You will be surprised to know that only a small sea-creature, oyster makes them. An oyster can crawl on the ground also. The biggest tragedy with this little creature is that fish of the sea or the bigger members of its own family eat it away. When the oyster comes to the sea-shore to save its life, man eats it. In order to protect itself, it forms a hard shell around its body with a unique substance called ‘nacre’ or mother of Pearl. Pearls are made within this hard cover.

             The discovery of pearls is an interesting story. Some four thousand years ago, a Chinese was suffering from hunger. To satiate his hunger he opened some oysters to eat. Inside one oyster he found one small round shining ball. The shinning ball-like thing was later on called pearl.

              Whenever, by chance, a sand particle goes inside the shell of an oyster and rubs against the animal’s tender body in order to soothe this irritation, it starts depositing layers upon layers of the shell material on this particle. These layers are made up of calcium carbonate. After sometime the formation of the pearl inside the shell is completed. The pearl so formed is round, white and shining. This is called pure pearl. However, the pearls are not essentially white only. Their colours may be black, white, rose, pale blue, yellow, and green, mauve also.

                Man has now developed some techniques of making artificial pearls. Under these techniques sand particles are introduced inside the shell. After two or three years, when the shell is taken out of water, a pearl is found inside it. These pearls are called cultured pearls. Japan has perfected the technique of making beautiful cultured pearls. Since pure natural pearls are very costly, generally we purchase pearls developed by these artificial techniques. On the 7th May, 1934, a pearl was found in Philippines measuring 23 cm with a diameter of 13 cm. This pearl weighed about 6.37 kg. This pearl was called Pearl of Laozi.