examined. The mixture of two or more compounds often produces a
decomposition by means of chemical _affinity_, a property which
different species of matter have to unite with each other; and which
is sometimes called _elective affinity_. Thus it may be observed,
chemists have not only the power of decomposing natural bodies, but of
producing by combination various other substances, such as are not
found in the kingdom of nature.


What do you mean by _decomposition_?

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.