Electrolysis, Laws of.
The following are the principal laws, originally discovered by
Faraday, and sometimes called Faraday's Laws of Electrolysis:
1. Electrolysis cannot take place unless the electrolyte is a conductor.
Conductor here means an electrolytic conductor, one that conducts by its
own molecules traveling, and being decomposed. (See Grothüss'
Hypothesis.)
II. The energy of the electrolytic action of the current is the same
wherever exercised in different parts of the circuit.
III. The same quantity of electricity--that is the same current for the
same period----- decomposes chemically equivalent quantities of the
bodies it decomposes, or the weights of elements separated in
electrolytes by the same quantity of electricity (in coulombs or some
equivalent unit) are to each other as their chemical equivalent.
IV. The quantity of a body decomposed in a given time is proportional to
the strength of the current.
To these may be added the following:
V. A definite and fixed electro-motive force is required for the
decomposition of each compound, greater for some and less for others.
Without sufficient electro-motive force expended on the molecule no
decomposition will take place. (See Current, Convective.)
Electrolyte.
A body susceptible of decomposition by the electric current, and capable
of electrolytic conduction. It must be a fluid body and therefore
capable of diffusion, and composite in composition. An elemental body
cannot be an electrolyte.
Electrolytic Analysis.
Chemical analysis by electrolysis. The quantitative separation of a
number of metals can be very effectively executed. Thus, suppose that a
solution of copper sulphate was to be analyzed. A measured portion of
the solution would be introduced into a weighed platinum vessel. The
vessel would be connected to the zinc plate terminal of a battery. From
the other terminal of the battery a wire would be brought and would
terminate in a plate of platinum. This would be immersed in the solution
in the vessel. As the current would pass the copper sulphate would be
decomposed and eventually all the copper would be deposited in a firm
coating on the platinum. The next operations would be to wash the metal
with distilled water, and eventually with alcohol, to dry and to weigh
the dish with the adherent copper. On subtracting the weight of the dish
alone from the weight of the dish and copper, the weight of the metallic
copper in the solution would be obtained.
In similar ways many other determinations are effected. The processes of
analysis include solution of the ores or other substances to be analyzed
and their conversion into proper form for electrolysis. Copper as just
described can be precipitated from the solution of its sulphate. For
iron and many other metals solutions of their double alkaline oxalates
are especially available forms for analysis.
The entire subject has been worked out in considerable detail by
Classen, to whose works reference should be made for details of
processes.
Electrolytic Convection.
It is sometimes observed that a single cell of Daniell battery, for
instance, or other source of electric current establishing too low a
potential difference for the decomposition of water seems to produce a
feeble but continuous decomposition. This is very unsatisfactorily
accounted for by the hydrogen as liberated combining with dissolved
oxygen. (Ganot.) The whole matter is obscure. (See Current, Convection.)