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There are three main groups of oils: animal, vegetable and mineral. Great quantities of animal oil come from whales, those enormous creatures of the sea which are the largest remaining animals in the world. To protect the whale from the cold of the Arctic seas, nature has provided it with a thick covering of fat called blubber. When the whale is killed, the blubber is stripped off and boiled down, either on board ship or on shore. It produces a great quantity of oil which can be made into food for human consumption. A few other creatures yield oil, but none so much as the whale. The livers of the cod and the halibut, two kinds of fish, yield nourishing oil. Both cod liver oil and halibut liver oil are given to sick children and other invalids who need certain vitamins. These oils may be bought at any chemist's.

Vegetable oil has been known from antiquity. No household can get on without it, for it is used in cooking. Perfumes may be made from the oils of certain flowers. Soaps are made from vegetable and animal oils.

To the ordinary man, one kind of oil may be as important as another. But when the politician or the engineer refers to oil, he almost always means mineral oil, the oil that drives tanks, aeroplanes and warships, motor-cars and diesel locomotives; the oil that is used to lubricate all kinds of machinery. This is the oil that has changed the life of the common man. When it is refined into petrol it is used to drive the internal combustion engine. To it we owe the existence of the motorcar, which has replaced the private carriage drawn by the horse. To it we owe the possibility of flying. I t has changed the methods of warfare on land and sea. This kind of oil comes out of the earth. Because it burns well, it is used as fuel and in some ways it is superior to coal in this respect. Many big ships now burn oil instead of coal. Because it burns brightly, it is used for illumination; countless homes are still illuminated with oil-burning lamps. Because it is very slippery, it is used for lubrication. Two metal surfaces rubbing together cause friction and heat ; but if they are separated by a thin film of oil, the friction and heat are reduced. No machine would work for long if it were not properly lubricated. The oil used for this purpose must be of the correct thickness; if it is too thin it will not give sufficient lubrication, and if it is too thick it will not reach all parts that must be lubricated.

The existence of oil wells has been known for a long time. Some of the Indians of North America used to collect and sell the oil from the wells of Pennsylvania. No one, however, seems to have realised the importance of this oil until it was found that paraffin-oil could be made from it ; this led to the development of the wells and to the making of enormous profits. When the internal combustion engine was invented, oil became of worldwide importance.

What was the origin of the oil which now drives our motor-cars and air-craft? Scientists are confident about the formation of coal, but they do not seem so sure when asked about oil. They think that the oil under the surface of the earth originated in the distant past, and was formed from living things in the sea. Countless billions of minute sea creatures and plants lived and sank to the sea bed. They were covered with huge deposits of mud; and by processes of chemistry, pressure and temperature were changed through long ages into what we know as oil. For these creatures to become oil, it was necessary that they should be imprisoned between layers of rock for an enormous length of time. The statement that oil originated in the sea is confirmed by a glance at a map showing the chief oilfields of the world; very few of them are far distant from the oceans of today. In some places gas and oil come up to the surface of the sea from its bed. The rocks in which oil is found are of marine origin too. They are sedimentary rocks, rocks which were laid down by the action of water on the bed of the ocean. Almost always the remains of shells, and other proofs of sea life, are found close to the oil. A very common sedimentary rock is called shale, which is a soft rock and was obviously formed by being deposited on the sea bed. And where there is shale there is likely to be oil.

Geologists, scientists who study rocks, indicate the likely places to the oil drillers. In some cases oil comes out of the ground without any drilling at all and has been used for hundreds of years. In the island of Trinidad the oil is in the form of asphalt, a substance used for making roads. Sir Walter Raleigh' visited the famous pitch lake of Trinidad in 1595; it is said to contain nine thousand million tons of asphalt. There are probably huge quantities of crude oil beneath the surface.

The king of the oilfield is the driller. He is a very skilled man. Sometimes he sends his drill more than a mile into the earth. During the process of drilling, gas and oil at great pressure may suddenly be met, and if this rushes out and catches fire the oil well may never be brought into operation at all. This danger is well known and steps are always taken to prevent it.

There is a lot of luck in drilling for oil. The drill may just miss the oil although it is near; on the other hand, it may strike oil at a fairly high level. When the drill goes down, it brings up soil. The samples of soil from various depths are examined for traces of oil. If they are disappointed at one place, the drillers go to another. Great sums of money have been spent, for example in the deserts of Egypt, in ' prospecting ' for oil. Sometimes little is found. When we buy a few gallons of petrol for our cars, we pay not only the cost of the petrol, but also part of the cost of the search that is always going on.

When the crude oil is obtained from the field, it is taken to the refineries to be treated. The commonest form of treatment is heating. When the oil is heated, the first vapours to rise are cooled and become the finest petrol. Petrol has a low boiling point; if a little is poured into the hand, it soon vaporizes. Gas that comes off the oil later is condensed into paraffin. Last of all the lubricating oils of various grades are produced. What remains is heavy oil that is used as fuel.

There are four main areas of the world where deposits of oil appear. The first is that of the Middle East, and includes the regions near the Caspian Sea, the Black Sea, the Red Sea and the Persian Gulf. Another is the area between North and South America, and the third, between Asia and Australia, includes the islands of Sumatra, Borneo and Java.

The fourth area is the part near the North Pole. When all the present oil-fields are exhausted, it is possible that this cold region may become the scene of oil activity. Yet the difficulties will be great, and the costs may be so high that no company will undertake the work. If progress in using atomic power to drive machines is fast enough, it is possible that oil-driven engines may give place to the new kind of engine. In that case the demand for oil will fall, the oilfields will gradually disappear, and the deposits at the North Pole may rest where they are for ever.

From Power and Progress by G. C. Thornley (Longman)