Water

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Water has always played an important in the lives of people. Early humans often made their homes near the waters edge. Sometimes they lived near the sea, sometimes along the banks of a river or stream. They caught fish with their spears and hooks. They hunted for birds and animals in the swaps, along both sides of the river. The first great discoveries of science, how to grow crops and how to rear animals, were made in the ancient land of Mesopotamia, ’the land between the rivers’. We now call that country Iraq. Much progress in science was also made in ancient Egypt, on both sides of the River Nile.

As well as being a source of food for people, water also makes it easier for us to travel. The earliest type of boat was probably a floating log. People could paddle along, using a flat stick as an oar. It is easier to move something in water, than it is to move it on land or in the air. In ancient times, people tied logs together with reeds to make rafts, on which they could carry their goods more easily.

Water is one of the commonest of all substances, and without it life would be impossible. The seas and oceans cover about seven-tenths of the Earth’s

Surface, but water is also contained in the so, in the atmosphere and in all living things. More than half of the human body consists of water, which also forms a large part of the food we eat, especially vegetables and fruit.

Water was believed to be an element, or distinct single substance, until 1781. Then the English chemist Henry Cavendish (1731-1810) proved that water was really a compound of two elements, hydrogen and oxygen. He did this by showing that when hydrogen was burned in oxygen, water was formed. In 1806, Sir Humphry Davy confirmed this this by electrolysis that is, he passed an electric current through water and obtained the two gases hydrogen and oxygen. Water is so unlike the elements composing it that Cavendish’s discovery was one of the most startling in the history of chemistry.

Water exists as a substance in three states : ice, which melts at 0 degrees Centigrade (32 degrees Fahrenheit) : liquid water ; and steam, which is formed when water boilsat 100 degrees Centigrade ( 212 degrees Fahrenheit). A gallon of fresh water weighs ten pounds and it is uuseful to remember the old rhyme ‘’a pint of pure water weighs a pound and a quarter ‘’. Water expands ( swells) on freezing by about 10%. At 4 degrees Centigrade it is at its densest, or occupies the least volume ( space ) ; and one cubic centimeter of it then weighs exactly one gramme.

Pure water is rarely found in nature. This is because water is able to dissolved so many substances from the air, the soil and the rocks. The saltness of sea water is cased by the mineral substances which are dissolved from the Earth’s surface by rivers and carried down the sea.  The sun’s heat causes the surface sea water to evaporate, or change into vapour, leaving behind the salt and other minerals. This explains why the seas are so much more salty than the rivers flowing into them.

BY Alice Moore.

 

 

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