The carbon compounds thus far considered have been mentioned to illustrate a few of the simpler or inorganic forms of carbon. We will now begin the study of organic chemistry or the compounds of carbon which are commonly found only in plant and animal substances.

Carbon has wonderful powers of combination with other chemical elements, and may combine with the same elements in thousands of different proportions. This property of carbon to form so many different compounds is considered one of the fundamental facts of chemistry upon which life depends. For example:

Properties of carbon monoxid.

Oxygen can combine with hydrogen in but two proportions - peroxid of hydrogen (H202) and water (H20) - while carbon and hydrogen can combine in more than a hundred different compounds. The simpler of these are acetylene (C2H2) and marsh gas or methane (CH4), which is the firedamp in mines.

The compounds containing carbon, hydrogen, and oxygen number into the Combining power of carbon thousands. A great many substances formed in plants contain these three elements, such as fruit-acids, alcohol, sugar, and fats.

Carbon and hydrogen compounds.