Charge, Free.
The charge borne by an insulated body, independent of surrounding
objects. Theoretically it is an impossibility. A charge always has its
compliment somewhere in surrounding objects. As a matter of convenience
and convention, where the complimentary charge is so distributed that
its influence is not perceptible the charge is called a free charge. If
connected to earth the free charge will leave the body. If the body is
connected with an electroscope the free charge will affect the same.
(See Charge, Bound.)
Charge, Residual.
When a Leyden jar or other condenser is discharged by the ordinary
method, after a few minutes standing a second discharge of less amount
can be obtained from it. This is due to what is known as the residual
charge. It seems to be connected in some way with the mechanical or
molecular distortion of the dielectric. The jarring of the dielectric
after discharge favors the rapidity of the action, diminishing the time
required for the appearance of the residual charge. The phenomenon, it
will be seen, is analogous to residual magnetism. This charge is the
reciprocal of electric absorption and depends for its amount upon the
nature of the dielectric. (See Absorption, Electric, and Capacity,
Residual.)
Synonym--Electric Residue.
Chatterton's Compound.
A cement used for cementing together layers or sheets of gutta percha,
and for similar purposes in splicing telegraph cables. Its formula is:
Stockholm Tar, 1 part.
Resin, 1 part.
Gutta Percha, 3 parts.
All parts by weight.
Chemical Change.
When bodies unite in the ratio of their chemical equivalents, so as to
represent the satisfying of affinity or the setting free of thermal or
other energy, which uniting is generally accompanied by sensible heat
and often by light, as in the ignition of a match, burning of a candle,
and, when the new compound exhibits new properties distinct from those
of its components, a chemical combination is indicated. More definitely
it is a change of relation of the atoms. Another form of chemical change
is decomposition, the reverse of combination, and requiring or absorbing
energy and producing several bodies of properties distinct from those of
the original compound. Thus in a voltaic battery chemical combination
and decomposition take place, with evolution of electric instead of
thermal energy.
Chemical Equivalent.
The quotient obtained by dividing the atomic weight, q. v., of an
element by its valency, q. v. Thus the atomic weight of oxygen is 16,
its valency is 2. its chemical equivalent is 8. It is the weight of the
element corresponding to a unit weight of hydrogen, either as replacing
it, or combining with it. In electro-chemical calculations the chemical
equivalent is often conveniently used to avoid the necessity of dividing
by the valency when atomic weights are used. The latter is really the
better practice. The atomic weights in the old system of chemical
nomenclature were chemical equivalents.