Page:International Library of Technology, Volume 93.djvu/76

 COMBUSTION AND FUELS

CHEMISTRY OF COMBUSTION

CHEMICAL ELEMENTS

LAWS OF CHEMICAL COMBINATIONS

1. Classes of Matter.—Every body, every mass of matter, is an element, a compound, or a mixture. Iron, silver, sulphur, and oxygen are elements; water, alcohol, wood, lime, and carbonic acid are compounds; air, granite, brass, petroleum, and mortar are mixtures.

2. Definition of Compound.—A compound may be decomposed or divided into separate substances. For example, if an electric current is passed through water, the water slowly disappears and two gases, oxygen and hydrogen, are formed. These gases are entirely unlike, and neither resembles the water from which it was produced. Likewise, lime can be divided into two substances, calcium and oxygen. Any substance that can thus be decomposed or divided into other substances is called a compound.

8. Definition of Element.—There are substances, however, that have never been decomposed into other substances. By no known process can sulphur be separated into other substances; neither can iron, gold, arsenic, and many others. Substances that have never been decomposed are called elements.