In chemical language, it means the separation of a compound body into its simple elements.
Give me an example.
Water may be decomposed, and reduced into oxygen and hydrogen,—both of them simple substances incapable of further decomposition.
Is not the work of decomposition perpetually going forward?
Yes; and combustion is one of the great agents in this work. By it animal and vegetable substances are converted into water and carbonic acid, by the union of their hydrogen and carbon with the oxygen of the air. These, in time, are again absorbed by vegetables, and again decomposed to set the oxygen at liberty to produce fresh combustions.
Of what use are the two remaining substances, Hydrogen and Carbon?
These are appropriated by the vegetative organs to their growth and nourishment, while the oxygen with which the carbon was combined is abundantly given off to purify the air and render it fit for the respiration of animals.
Give me an idea of the mode in which Chemists ascertain the affinity of bodies, by relating an experiment.
Dissolve a tea-spoonful of sugar of lead in water, and pour the clear solution into a decanter or large glass bottle. Then take a small piece of zinc, and twist round it some brass or copper wire, so as to let the ends of the wire depend from it in any agreeable form. Suspend the zinc and wire in the solution which has been prepared; in a short time, metallic lead will deposit itself on the zinc and along the wire. This is a beautiful illustration of chemical affinity; the acid, which constitutes a part of the sugar of lead, has a stronger affinity for the zinc than for the lead, and, consequently, will combine with the zinc, and form a compound which remains in solution, while the lead is precipitated on the zinc and wire in the form of a brilliant tree of metal.
Affinity, in chemistry, that attraction which takes place between the elements of bodies, and forms compounds.