3. The quantity of an ion liberated is equal to the electro-chemical equivalent of the ion multiplied by the total quantity of electricity that has passed.
Electric Osmose.—Porret observed that if a strong current be led into certain liquids as if to electrolyze them, a porous partition being placed between the electrodes, the current mechanically carries part of the liquid through the porous diaphragm, so that the liquid is forced to a higher level on one side than on the other. This phenomenon is known as electric osmose.
Electric Distillation.—Closely connected with the preceding phenomenon is that of the electric distillation of liquids. It was noticed by Beccaria that an electrified liquid evaporates more rapidly than one not electrified.
Gernez has recently shown that in a bent closed tube, containing two portions of liquid, one of which is made highly + and the other highly -, the liquid passes over from + to -. This apparent distillation is not due to difference of temperature, nor does it depend on the extent of surface exposed, but is effected by a slow creeping of the liquid along the interior surface of the glass tubes. Bad conductors, such as turpentine, do not thus pass over.
Muscular Contractions.—It was discovered in 1678 that when a portion of muscle of a frog’s leg, hanging by a thread of nerve bound with a silver wire, was held over a copper support so that both nerve and wire touched the copper, the muscle immediately contracted.
More than a century later Galvani’s attention was drawn to the subject by his observation of spasmodic contractions in the legs of freshly killed frogs under the influence of the “return shock” experienced every time a neighboring electric machine was discharged.
The limbs of the frog, prepared as directed by Galvani, are shown in fig. 92. After the animal has been killed the hind limbs are detached and skinned; the crural nerves and their attachments to the lumbar vertebrae remaining. For some hours after death the limbs retain their contractile power. The frog’s limbs thus prepared form an excessively delicate galvanoscope.
Electroplating.—This is the process of depositing a layer or coating of a rarer metal upon the surface of a baser, or of a metal upon any conducting surface, by electrolysis.
The electric current used may be obtained from a battery or other source. The battery has its positive plate connected to a rod extending across a trough or tank containing the plating bath.