The Romance of Modern Chemistry

NATURE’S STORES OF FUEL wood, apart from the large amount of water which it contains, consists chiefly of cellulose, a compound of the three elements, carbon, hydrogen, and oxygen. If the wood dies and is allowed to lie in the soil where it has grown, a remarkable series of chemical changes sets in. In many cases the fallen forests and jungles of the past have been submerged and then covered over with alluvial deposits of clay and sand, so that what was once a luxuriant vegetation on the surface is now buried many feet below. Now when wood or any other vegetable matter con- taining cellulose is kept below water or in a moist soil, the relative proportions of the carbon, hydrogen, and oxygen which made up the cellulose begin to change. De- composition and fermentation set in, the hydrogen is gradually eliminated in the form of marsh gas—a com- bustible compound of carbon and hydrogen—and the oxygen in the form of carbon dioxide. Any one who pokes a stick into a stagnant pool at the bottom of which vegetable matter is decomposing will observe bubbles of gas rising to the surface. These bubbles have been examined by chemists, and are found actually to contain carbon dioxide and marsh gas. The result of these slow changes—extending over a long period—is that instead of cellulose there is left a carbonaceous mass containing a very much higher per- centage of carbon than the original wood. If the de- composition has been going on for a very long time and at some depth below the surface, the product is a compact coal, containing relatively small quantities of hydrogen and oxygen. Vegetable matter of more recent date will not have been carbonised to the same extent, and will have reached the stage represented by brown coal or 132