474

Decomposition and recnmpositim of Water. [Book IV.

ception of the ether, this device is a modification of the air machines Nos.174 and 175, figured at page 380.

The vapor of mercury has been tried as a Substitute for steam, butwithout mueh success. This metal boils at 660°.

Another source of power has been sought in the tremendous force withwhich the liquefied and solidified gases expand at common temperatures.Liquid carbonic acid, at the low temperature of 32°, has been found toexert a force equivalent to thirty five atmospheres ! and every incrementof heat adds to its energy. No very practical mode of employing thisforce as a mechanical agent has yet been matured.

The alternate decomposition and recomposition of water has also beensuggested. By decomposing this liquid by galvanic electricity, oxygenand hydroeen gases are produced in the exact proportions in which theycombine in water. If these gases be made to occupy the interior of acylinder when the piston is raised, and the electric spark be then passedthrough them, they instantly become Condensed into a few drops of water,and an almost perfect vacuum is the result, when the atmosphere acts onthe piston. The water is then to be reconverted into its constituent gases,and the Operation repeated. See “ The Chemist, ” for 1825. For furtherand more recent Information respecting motive engines, consult the Re-pertory of Arts, Hebert’s Register of Arts, London Mechanics’ Magazine,and the Journal of the Franklin Institute.

END OP THE -j^OURTH BOOK.