chloride.

Electrolysis is also used to some extent in reducing metals from
their ores, in bleaching fibre, in manufacturing hydrogen and
oxygen from water, and in the chemical treatment of sewage.





CHAPTER VI.

THE TELEGRAPH AND TELEPHONE.


Like the "philosopher's stone," the "elixir of youth," and
"perpetual motion," the telegraph was long a dream of the
imagination. In the sixteenth century, if not before, it was
believed that two magnetic needles could be made sympathetic, so
that when one was moved the other would likewise move, however far
apart they were, and thus enable two distant friends to
communicate their minds to one another.

The idea was prophetic, although the means of giving effect to it
were mistaken. It became practicable, however, when Oersted
discovered that a magnetic needle could be swung to one side or
the other by an electric current passing near it.

The illustrious Laplace was the first to suggest a telegraph on
this principle. A wire connecting the two poles of a battery is