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.
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:
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.