Carbon (C) is an element with which we are more familiar; coal, charcoal, and wood are common forms. Lead-pencils do not really contain lead at all but another form of carbon called graphite. Strangest of all, the diamond is carbon, too, though not a common form.
Carbon is (except in the diamond) a black solid, not soluble in any thing. At ordinary temperature it is very inactive. When heated, however, it unites readily with oxygen, (that is, it burns) and forms an oxide which is called carbon dioxide a compound very necessary to plants, as we shall see later.
What is carbon for? Carbon's importance to biology is due to the fact that it is a part of all organic substances, combining with hydrogen, nitrogen, and oxygen and other elements to form all plant and animal tissues and many of their foods.
We know that if any plant or animal substance is partly burned a black solid is produced. This, in every case, is carbon. We also know that if the burning is continued the carbon will disappear. This means that it becomes oxidized into carbon dioxide, which is an invisible gas. Plants alone have the power to obtain their carbon from the carbon dioxide of the air. Animals depend entirely on plant foods for the carbon compounds which are necessary for their life
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