Current Production by Chemical Action.-The simplest method of current generation is by various forms of chemical current producers which may be either primary or secondary in character. A simple form of cell is shown in section at Fig. 3, A, and as the action of all devices of this character is based on the same principles it will be well to consider the method of producing electricity by the chemical action of a fluid upon a metal. The simple cell shown

Fig. 2.-Diagrams Outlining How Current Voltage is Reduced by Increasing Resistance in Circuit. A-Water Flow Reduced by Shut-off Valve. B-Electric Flow Reduced by Rheostat, an Equivalent of the Valve in the Water System.

consists of a container which is filled with an electrolyte which may be either an alkali or acid solution. Immersed in the liquid are two plates of metal, one being of copper, the other zinc. A vire is attached to each plate by means of suitable screw terminals.

If the ends of the plates which are not immersed in the solution are joined together a chemical action will take place between the electrolyte and the zinc plate; in fact, any form of cell consists of dissimilar elements which are capable of conducting electricity im

mersed in a liquid which will act on one of them more than the other. The chemical action of electrolyte on the zinc liberates gas bubbles which are charged with electricity and which deposit themselves on the copper plate. The copper element serves merely as a collecting member and is termed the "positive" plate, while the zinc which is acted upon by the solution is termed the "negative" member. The flow of current is from the zinc to the copper plate through

A

Fig. 3.-Simple Primary Cell Used to Produce Electric Current.
Form to Show Principle of Current Production by Chemical Action.
B-Dry Cell, the Type Suitable for Automobile Service.

the electrolyte and it is returned from the copper plate to the zinc element by the wiring which comprises the external circuit.

While in the cell shown zinc and copper are used, any other combination of metals between which there exists a difference in electrical condition when one of them is acted upon by a salt or acid may be employed. Any salt or acid solution will act as an electrolyte if it will combine chemically with one of the elements and if it does not at the same time offer too great a resistance to the passage of the electric current. The current strength will vary with the nature of the elements used, and will have a higher value

when the chemical action is more pronounced between the negative member and the electrolyte.

As the vibrations which obtain when the automobile is driven over highways makes it difficult to use cells in which there is a surplus of liquid, a form of cell has been devised in which the liquid electrolyte is replaced by a solid substance which cannot splash out of the container even if the cell is not carefully sealed. A current producer of this nature is depicted in section at Fig. 3, B. This is known as a dry cell and consists of a zinc can in the center of which a carbon rod is placed. The electrolyte is held close to the zinc or negative member by an absorbent lining of blotting paper, and the carbon rod is surrounded by some depolarizing material. The top of the cell is sealed with pitch to prevent loss of depolarizer.

The depolarizer is needed that the cell may continue to generate current. When the circuit of a simple cell is completed the current generation is brisker than after the cell has been producing electricity for a time. While the cell has been in action the positive element becomes covered with bubbles of hydrogen gas, which is a poor conductor of electricity and tends to decrease the current output of the cell. To prevent these bubbles from interfering with current generation some means must be provided for disposing of the gas. In dry cells the hydrogen gas that causes polarization is combined with oxygen gas evolved by the depolarizing medium and the combination of these two gases produces water which does not interfere with the action of the cell. Carbon is used in a dry cell instead of copper because it is a cheaper material and the electrolyte is a mixture of salammoniac and chloride of zinc which is held in intimate contact with the zinc shell which forms the negative element by the blotting paper lining.

Wiring Dry Cells.-When dry cells are used for ignition there are two practical methods of connecting these up. At least four dry cells are necessary to secure satisfactory ignition and much more energetic explosions will be obtained if five or six are used. The common method is to join the cells together in series as shown at Fig. 4, A. When connecting in this manner the carbon terminal of one battery is always coupled to the zinc binding post of its

Fig. 4. Methods of Connecting Dry Cells and Precautions to be Observed When Wiring.

neighbor. Connection would be made from the carbon of the first cell to the zine of the second, from the carbon of the second to the zinc of the third, and from the carbon of the third to the zinc of the fourth, this leaving the zinc terminal on the first cell and the carbon terminal on the fourth cell free to be joined to the external circuit. When dry cells are connected in series the

voltage is augmented, that of one cell being multiplied by the number so joined. The amperage remains the same as that of one cell. If a dry cell has a potential of 14 volts, a battery composed of four cells would show 5 volts. When dry batteries are used for lighting purposes or for igniting multiple cylinder engines, in order to obtain better results, they are connected in series multiple, as shown at B. Three sets of cells joined in series are placed side by side with the free carbons at one end in line and the zincs at the other also in line. The three carbons are then joined together by one wire, the three zinc terminals by another. When joined in this manner the battery has a voltage equal to that of four cells and an amperage equal to that of three cells. If a series connected battery as at A indicates 5 volts and 20 amperes, the series multiple connection at B will indicate 5 volts and 60 amperes. When cells are joined in multiple the drain on any one cell is reduced and it is not so likely to become exhausted as when four are used in series. The points to be watched out for when installing dry batteries are clearly outlined at the bottom of Fig. 4. It will be seen that it is not desirable for terminals to come in contact with each other or with the sides of the box or is it conducive to good ignition to have the zinc shells in contact. A loose terminal on any one of the batteries will result in irregular ignition while a broken wire will interrupt it altogether. If the insulation is frayed where a wire passes through a hole in a metal battery box trouble may be experienced due to short circuiting of the current between the bare wire and the steel box, which may be grounded.

One of the disadvantages of primary cells, as those types which utilize zinc as a negative element are called, is that the chemical action produces deterioration and waste of material by oxidization. Dry cells are usually proportioned so that the electrolyte and depolarizing materials become weaker as the zine is used and when a dry cell is exhausted it is not profitable to attempt to recharge it because new ones can be obtained at a lower cost than the expense of renewing the worn elements would be.

The number of dry cells necessary will vary with the system of ignition employed and the size of the motor. While two or three