Thus we find that the force which we term electricity, developed from
the oxidation of zinc, or any other matter, by oxidation, primarily
comes from the sun rays.
Coal is generally supposed to be of vegetable origin, and the caloric
occluded in it is derived from the same source as that embodied in
charcoal. Now when we burn coal under a steam boiler, the carbon and
hydrogen are oxidized, and the static caloric set free. A portion of
this caloric passes through the shell or tubes of the boilers, and
increases the molecular velocity of the water; increased activity of
the molecules tends to separate them to a greater distance from each
other. When the molecular velocity of the water acquires the degree
indicated by a temperature of 212 degrees F., the water passes from
the fluid to the gaseous state, and in doing so expands to 1,696 times
its bulk. Now if the steam so developed be confined under a pressure
of 105 pounds to the square inch, the water will not vaporize until a
molecular velocity is attained indicated by a temperature of 312 deg. F.
(Spons' "Engineering," D2, page 418), and then the expansion is only
253 times its bulk. By using this steam, in a steam engine, the
caloric in the steam tends to push the molecules of which it is
composed into an ultimate expansion of 1,696 times the bulk of the
water from which it was generated, and this force acts upon the piston
and does the work.
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