A very important type of potential energy: Coal
-> Coal is a hard black substance which we take from below the surface of the earth and burn as fuel. People have known the burning property of coal for centuries. We know, for example, that the Chinese used it for smelting copper (Cu) at least 3000 years ago. In Europe, they started using coal in the 12th century in England.
But people used coal the most after the invention of the steam engine, during the 18th and 19th centuries. Towards the end of the 19th century, coal was the leading fuel of the world. Today, coal, petroleum and natural gas are fuels of equal importance.
One advantage of coal is that we can find it closer to the surface than petroleum and natural gas. Therefore, we can mine coal: that is, take it from under the earth, less expensively. A second advantage of coal is that there is more of it than there is of the other two fuels.
The Kinds Of Coals
There are four kinds of coal in the world. These are lignite, subbituminous coal, bituminous coal and anthracite.
Lignite gives little heat and contains about 75% elementary carbon.
Subbituminous coal contains less moisture than lignite and produces (gives out) more heat.
Bituminous coal contains less than 86% carbon.
Anthracite is the coal with the highest carbon content (86 % or more) and gives the most heat. Anthracite also bums slowly and thus maintains – keeps – a uniform and constant fire. These properties of anthracite make il the most preferable kind of coal, especially for domestic uses» in other words, for uses in
One disadvantage of anthracite, however, is that there is less of it than there is of the other kinds of coal.
We can use coal directly in domestic fires, to smelt iron (Fe) in turbines, or to produce steam in steam engines.
Our coal supply is large. There is still lots of coal under the ground. We’ll probably have
enough of it for about 400 years.