Chemical change is due to the action of chemical force, which like other forces cannot be described; but is known by its effects. It is quite different, however, from the other forces of gravitation, heat, light, and electricity.

When two elements or compounds act chemically upon each other (disintegrate) or are treated in some special way, they are generally altered in appearance and state.

To illustrate: A mixture of oxygen and hydrogen is still a gas, but a chemical compound of oxygen and hydrogen is water, or a liquid. When zinc is added to muriatic acid ("raw acid") heat is given off, a gas is generated, and the zinc combines with the acid. The resulting compound, zinc chloride, is different from the original substances. The equation is:

Zn

+

2HC1

ZnCl2

+

2 H

Zinc

Hydrochloric Acid

Zinc Chloride

Hydrogen

These illustrations show that chemical action is distinguished from all other action: first, by producing a compound with properties entirely changed from those of the substances or compounds originally used; second, by the fact that it takes place between definite weights and volumes.