=Charge.= The quantity of electricity that is present on the surface of a body or conductor.
The component chemical parts that are employed to excite the elements of a cell in generating electric current.
=Charge, Residual.= After a Leyden-jar, or other condenser, has been discharged by the ordinary methods, a second discharge (of less amount) can be had after a few minutes’ waiting. This is due to what is known as the residual charge, and is connected in some way with the molecular distortion of the dielectric.
=Chemical Change.= When bodies unite so as to satisfy affinity, or to bring about the freeing of thermal or other energy, the union is usually accompanied by sensible heat or light. Sulphuric acid added to water produces heat; a match in burning produces light. Another form of chemical change is decomposition or separation (the reverse of combination), such as takes place in the voltaic-battery, the electro-plating bath, and other forms of electrolysis. This is not accompanied by heat or light, but by the evolution of electricity.
=Chemical Element.= (_See_ Element, Chemical.)
=Chemistry.= The science which treats of the atomic and molecular relations of the elements and their chemical compounds. Chemistry is divided into many departments, but electro-chemistry treats only of the science wherein electricity plays an active part, such as batteries, electro-plating, and electro-metallurgy.
=Circle, Magic.= A form of electro-magnet. It is a thick circle of round iron used in connection with a magnetized coil to illustrate electro-magnetic attraction.
=Circuit.= A conducting-path for electric currents. Properly speaking, a complete circuit has the ends joined, and includes a source of current, an apparatus, and other elements introduced in the path. When the circuit is complete it is called active. The term circuit is also applied to portions of a true circuit--as, an internal or external circuit.
=Circuit, Astatic.= A circuit so wound, with reference to the direction of the currents passing through it, that the terrestrial or other lines of force have no directive effect upon it.
=Circuit-breaker.= Any apparatus for opening and closing a circuit, such as switches, automatic cut-outs, lightning-arresters, and the like.