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are several reasons for considering this theory. The most important is that chemical analysis of a discharged plate has shown large quantities of lead sulphate to exist. The fact that the density of the electrolyte becomes less during the discharge of the cell shows that sulphuric acid is consumed and that water remains. The specific gravity of the electrolyte is greatest when the cell is fully charged. This demonstrates conclusively that during charging the sulphate has been driven out of the plates and into the electrolyte. When a battery is discharged, the sulphate, having been absorbed by the plates, results in a lower specific gravity of the electrolyte. Then, again, considering the matter from an electro-chemist's point of view, it is known that the combination of oxygen and lead as lead oxide would not liberate sufficient electrical energy to account for the voltage of the current produced by the battery on discharge.
Planté, or Formed Plates.—One of the first difficulties met with and one that militated against the development of the practical or commercial type of battery using Planté plates was the great length of time needed and the expensive means of generating the forming current. Later the plates were treated with nitric acid to facilitate the forming action. Other processes have been developed to hasten the formation. In addition to the chemical treatment, which consists of immersing the lead plates in a pickling bath to produce an oxidization before the current acts upon them, there is a mechanical action which will produce the same result and hasten formation. Laminated plates composed of ribbons of lead will form quicker than the solid lead plates, as will elements made up of lead wires or plates where the surface has been grooved with some forming-tool. · An electrolytic process consists of making the plate of a lead alloy and eating the foreign matter away to leave a porous lead plate. These processes are described more in detail in the next chapter, which deals specifically with storage baftery plate construction.
Faure, or Pasted Plates.—As soon as it was realized that the result of the forming current was the production of lead peroxide on one of the plates, two men, Camille Faure in France and Charles F. Brush in the United States, working independently of
each other, devised a process of plate manufacture that materially reduced the cost of construction. Instead of forming the active material by expensive and time-consuming alternating charges and discharges, the common oxides of lead were applied to the surface of the plate in the form of paste, so that the work required of the electric current was reduced appreciably and considerable weight reduction obtained. Litharge, which is rich in lead, was selected for the negative plates, while red lead, which is oxidized more, was used on the plates intended to be positives. The pastes were composed of the oxides mixed with dilute sulphuric acid in the proportion about one part acid to four of water. Such a paste sets very quickly, and only small quantities can be prepared at a time. When the Faure process, as it is called, was first developed, it was believed that the Planté type of plate would be discarded. It was found by practical experience that the new structure developed faults that were not present in the older formation. Pasted plates of early development were found to bend or warp, to enlarge and to shed the active material. In order to eliminate these faults, various ingenious grid patterns were devised.
When storage cells are to be used in automobile work they are combined in a single containing member, as shown at Fig. 4, A, which is a part sectional view of storage battery. The main containing member, a box of wood is divided into three parts by cell jars of hard rubber. Each of these compartments serves to hold the elements comprising one cell. The positive and negative plates are spaced apart by wooden and hard rubber separators, which prevent short circuiting between the plates. After the elements have been put in place in the compartments forming the individual cells of the battery, the top of the jar is sealed by pouring a compound of pitch and rosin, or asphaltum, over cover plates of hard rubber, which keeps the sealing material from running into the cells and on the plates. Vents are provided over each cell, through which gases, produced by charging or discharging, are allowed to escape. These are so formed that while free pas.sage of gas is provided for, it is not possible for the electrolyte to splash out when the vehicle is in motion.
It will be evident that this method of sealing would not be
line Cell. and Ignition Battery. B—Internal Construction of Edison Alka
ciples. A—Part Sectional View of Automobile Starting, Lighting Fig. 4.-Illustrating Standard Batteries Operating on Different Prin
practical on a primary cell where the members attacked by the acid had to be replaced from time to time, but in a storage battery only the electrolyte need be renewed. When the plates are discharged they are regenerated by passing a current of electricity through them. New electrolyte can be easily inserted through vents in which caps are screwed. The cells of which a storage battery is composed are nearly always joined together at the factory with bars of lead, which are burned in place, and only two free terminals are provided by which the battery is coupled to the outer circuit.
The capacity of a storage battery depends upon the area and the number of plates per cell, while the potential or voltage is determined by the number of cells joined in series to form the battery. Each cell has a difference of potential of two and two-tenths volts when fully charged, therefore a two-cell battery will deliver a current of four and four-tenths volts, and a threecell type as shown at Fig. 4, A, will give about six and six-tenths volts between the terminals. While dry cells are often connected in parallel, storage batteries should not be coupled in this manner, as the sets do not divide the load properly unless all the cells are equal in charge, capacity and general condition. A bad cell. may so weaken one set that the other set will discharge through it, reducing the charge seriously. When sets are used in parallel it is advisable to test the sets separately. If one set is doing a large proportion of the work, the gravity of the electrolyte will be different in the sets. It is advisable to change parallel sets to series, when practicable, for charging at terminal stations. This insures the same charge being put in each set. For similar reasons all the cells used in a set should be in the same condition and equally well charged to prevent one or more cells reversing in service.
The Edison Storage Battery.—The fundamental principle of the Edison storage battery shown at Fig. 4, B, is the oxidization and reduction of metals in an electrolyte which neither combines with nor dissolves either the active materials or their oxides. Also, an electrolyte which, notwithstanding its decomposition by the action of the electric current, is immediately re-formed in equal quantity, and is, therefore, a practically constant element with
out change of density or conductivity over long periods of time. A storage battery is commonly looked upon as a receptacle in which to store electricity. Electricity is not concrete matter. In fact, nobody knows just what it is. Therefore, in the general apprehension of the term, it is not stored. Electricity simply causes a chemical change to be effected in certain substances, when it is caused to flow through them. These substances in endeavoring return to their original state, produce electricity.
The following elementary explanation of the action of the nonacid battery is given by the Edison Storage Battery Company, and is so simply expressed and easily understood that it is reproduced in full. If the reader grasps the principles expressed, he will . have no difficulty in understanding the chemical action that results in current production.
“Suppose we place two pieces of very thin, bright steel out of doors for a few weeks. They become “rusted. The action of the oxygen on the outer layer of the metal has formed it into an oxide commonly known as “rust.' Now let us place these two pieces of steel in a solution composed of potash and water, and connect them by wires to a small dynamo. The electricity, in flowing from the dynamo through the solution, from one of the plates to the other and back to the dynamo, changes the rust to metallic iron on one of the plates, but causes the other plate to become “rusted’ twice as much as before. Now let us disconnect the plates from the dynamo and connect them, by means of pieces of wire, to an ammeter (an instrument for measuring electricity). Instantly, the excess of oxygen in the rust on the one plate commences to pass back to the bright plate and, by so doing, causes electricity to be generated. Why? Nobody really knows. We have now charged and discharged a primitive storage battery.
“Instead of two thin rusted steel plates, let us mount, say, one hundred such plates, equidistantly spaced, on one rool, anised one hundred more on another rod. Now interpose the two groups so the plates of the one group will not touch those of the ot'ier and immerse them in a solution of potash. When connected to our dynamo the electricity will flow from one group, through the solution, to the other group, converting the oxide of one group to