xygen.

CAROLINE.

But I do not see whence the rubber obtains oxygen, for there is neither
acid nor water used in the common machine, and I always understood that
the electricity was excited by the friction.

MRS. B.

It appears that by friction the rubber obtains oxygen from the
atmosphere, which is partly composed of that element. The oxygen
combines with the amalgam of the rubber, which is of a metallic nature,
much in the same way as the oxygen of the acid combines with the zinc in
the Voltaic battery, and it is thus that the two electricities are
disengaged.

CAROLINE.

But, if the electricities of both machines are similar, why not use the
common machine for chemical decompositions?

MRS. B.

Though its effects are similar to those of the Voltaic battery, they are
incomparably weaker. Indeed Dr. Wollaston, in using it for chemical
decompositions, was obliged to act upon the most minute quantities of
matter, and though the result was satisfactory in proving the similarity
of its effects to those of the Voltaic battery, these effects were too
small in extent to be in any considerable degree applicable to chemical
decomposition.

CAROLINE.

How terrible, then, the shock must be from a Voltaic battery, since it
is so much more powerful than an electrical machine!

MRS. B.

It is not nearly so formidable as you think; at least it is by no means
proportional to the chemical effect. The great superiority of the
Voltaic battery consists in the large _quantity_ of electricity that
passes; but in regard to the _rapidity_ or _intensity_ of the charge, it
is greatly surpassed by the common electrical machine. It would seem
that the shock or sensation depends chiefly upon the intensity; whilst,
on the contrary, for chemical purposes, it is quantity which is
required. In the Voltaic battery, the electricity, though copious, is so
weak as not to be able to force its way through the fluid which
separates the plates, whilst that of a common machine will pass through
any space of water.

CAROLINE.

Would not it be possible to increase the intensity of the Voltaic
battery till it should equal that of the common machine?

MRS. B.

It can actually be increased till it imitates a weak electrical machine,
so as to produce a visible spark when accumulated in a Leyden jar. But
it can never be raised sufficiently to pass through any considerable
extent of air, because of the ready communication through the fluids
e