WET BATTERIES.
Wet batteries are divided into one-liquid bat teries and two-liquid batteries. The former are those which contain one homogeneous elec trolyte; the latter have two distinct electro lytes, and the cell is usually divided into two parts by a porous cup which contains one of the metallic electrodes and one of the electro lytes.
Among the prin cipal batteries now in use for economic purposes and in general laboratory work are the following: Smee.— A cell consisting of a platinum plate hung between two zinc plates in an elec trolyte of dilute sulphuric acid. The platinum plate is roughened by an electro-deposit of platinum, forming a surface to which hydrogen bubbles will not adhere. The platinum is often substituted by silver, which, however, is roughened by depositing a skin of platinum. A variation of this cell has a grid of carbon rods instead of the platinum plate, the surface of the rods being made hydrogen-proof by carbonizing oa them jackets of velveteen.
Bichromate, consisting of a zinc plate sus pended between two carbon plates, which are gripped together at the top above the jar. The electrolyte used is a mixture of separately pre pared solutions of sulphuric acid and of po tassium bichromate. With this cell the zinc plates have to be raised out of the electrolyte when the battery is not in use, to prevent con tinuous chemical action, and therefore waste of energy.
Leclanche has a solution of sal-ammoniac (ammonium chloride) as the electrolyte, and into this dips a zinc bar in one corner of the square glass jar. The other pole is a bar of carbon within a porous jar, the space within being closely packed with a mixture of manganese dioxide and powder coke. The whole is immersed in the electrolyte. The oxy gen escaping from the dioxide prevents polar ization of the cell, and the porous jar prevents the oxygen from reaching the zinc, while op posing no barrier to the passage of the electric current. This cell is useful only for inter mittent work, such as ringing bells and buzzers.
Harrison.— The negative (internal) pole or cathode is a rod of hard lead around which is compressed a jacket of lead peroxide. The other pole or anode is of zinc, cast in the form of 'a very thick tumbler which is supported by an amalgamated copper rod running down through it and riveted in the centre of the bottom. Around this rod the tumbler is partly filled by pouring in melted zinc amalgam. The electrolyte is dilute, sulphuric acid, or a solution of potassium bisulphate, or of sodium bisulphate. This is a very powerful battery.
Caustic Alkali or Copper Oxide C ells.— This type of cell was introduced in 1881 by Lalande and Chaperon, France. Their cell con sisted of a glass jar, in the bottom of which the oxide of copper was contained in an iron cup; the zinc plate was supported in the solution of caustic potash by a wire, from the cover of the jar. To prevent the carbonic acid gas of the air from combining with the caustic potash, the solution was covered with a layer of petroleum oil. This cell has undergone many modifica tions at the hands of Edison, Gordon and others.
Edison Primary Battery—An oxide of copper battery. The elements employed in it are zinc and black oxide of copper. The solu tion is of high grade caustic soda, in the pro portion of 25 parts of caustic soda to 100 parts of water. The initial electromotive force of these cells is .98 volt; on closed circuit, 0.7 volt. Their internal resistance varies with the size of the plates from .09 ohm to .02 ohm. The capacity of these cells, as commercially constructed, ranges from 50 to 600 ampere hours. The oxide of copper cell has the ae vantage that its internal resistance falls with use, inasmuch as the continued reduction of metallic oxide from the oxide of copper in creases the conductivity of the plate; in prac tice, however, a film of metallic copper is de posited in advance on the copper oxide plate to ensure a low resistance at the start.