Electric Gas Lighting Part 5

Before entering into a description of the various batteries used in electric gas lighting, it will be well to briefly consider a few simple electrical rules bearing upon the subject.

A current of electricity has _electromotive force_, or _difference of potential_ figured in _volts_, and _current_ figured in _amperes_.

For example we will use the _water_ a.n.a.logy (Fig. 49). Two tanks, _A_ _B_, on the same level, are connected by a pipe _C_.

Supposing tank _A_ be filled with water and the pipe, _C_, to be opened; the water will flow along _C_ into _B_ until the level in each tank is equal. So long as there is a difference of level, there will be a pressure in _C_, owing to the water behind it.

Replacing the tanks _A_ and _B_ by unequally electrified bodies, and the pipe _C_ by a conductor of electricity, the flow of water is represented by the tendency of the electrified bodies to equalize themselves by a flow of current along the conductor, _C_.

To sum up: The difference of level is now difference of potential, the pounds pressure along the pipe being expressed as electromotive force in _volts_.

[Ill.u.s.tration: FIG. 49.]

The quant.i.ty of water flowing along the pipe is measured, as electricity, in amperes. As the quant.i.ty of water pa.s.sing in a given time is regulated by the size of the pipe and its own pressure, so the quant.i.ty of electricity is also regulated. A conductor of electricity offers resistance to the flow of current according to its sectional area and the material of which it is composed, this resistance being expressed in _ohms_. The greater the voltage and lower the resistance, the more current. This law, and its kindred applications, are expressed as follows:

_C = E/R._

_C_ is current in amperes, _E_ electromotive force in volts, and _R_ resistance in ohms.

Thus a wire with a resistance of 50 ohms would pa.s.s 2 amperes with an electromotive force of 100 volts. To find resistance when other two factors are known, the formula is

_R = E/C._

In selecting a battery for work, regard must be made to the current required, and its period of flow. For energizing a gas lighting primary coil, the current must be large, but is only required occasionally, the battery standing idle for long periods. In this case the cla.s.s called open circuit cells are preferable, as they contain no strong acids and do not deteriorate to any extent when not in use. Of such cla.s.s is the Leclanche-Samson, Monarch, carbon cylinder, and most so-called dry cells. As the resistance in a conductor affects the current flow, so it does in a battery cell; the internal resistance of a battery is determined by its size, proximity of the elements, etc.

Cells with small zincs and porous cups are of high internal resistance, those with large sheet zincs and big carbon surfaces, of low internal resistance. As the primary coil used in gas lighting is never much over one ohm, a cell of low internal resistance should be selected. But as the wires leading to the burners must be taken into account, a number of cells should be used to produce enough electromotive force to overcome the added resistance. Now battery cells can be arranged in a variety of ways--in series for higher electromotive force, and in multiple--for greater current.

[Ill.u.s.tration: FIG. 50.]

Fig. 50 represents the series arrangement; here the zinc of one cell is connected to the carbon of the next; this adds the electromotive forces together and thus gives greater ability to overcome resistance, but it also adds together the resistance of each cell. Thus 4 cells, each 2 volts and of one-half ohm internal resistance, would, in series, have an E. M. F. of 8 volts and an internal resistance of 2 ohms, current 4 amperes. Fig. 51 shows four cells in multiple, the zinc of each cell and the carbons of each cell are connected. Here the result would be but 2 volts, but the internal resistance would be only one-quarter, viz: one-eighth of an ohm, current 16 amperes.

[Ill.u.s.tration: FIG. 51.]

The readiest rule for connecting a battery is to arrange it according to the resistance of the line or outside wiring. So as we will have to use house-wiring far exceeding in length that on the coil, and probably of less diameter. Therefore the series arrangement will be the one to use, and not less than four cells of a low-resistance battery.

THE LECLANCHE.

This battery consists of a carbon rod surrounded by granular peroxide of manganese forming the positive pole and a piece of zinc for the negative pole, both elements being immersed in a solution of sal ammoniac (chloride of ammonia). If a wire be run _outside_ the solution and connecting the carbon and zinc, a current of electricity flows along it. The chemical action taking place is as follows: The zinc combines with the chlorine of the solution, liberating free hydrogen and ammonia. The hydrogen appears at the carbon, where it is acted upon by the oxygen of the peroxide of manganese. If too much current is taken from the cell, that is, if the wire or circuit be of too low resistance, the oxidizing action of the peroxide is not rapid enough, and a film of hydrogen, which is a poor conductor, forms over the carbon and increases the resistance of the battery--also setting up what is termed "local action" (actually, a battery opposing a battery).

After a rest, the hydrogen is absorbed, but a cell rarely regains its pristine activity after too severe demands upon it. The original Leclanche batteries were imported from France, the home of the inventor, but of recent years they are made in the United States, England and Germany. The most important point to be considered in a galvanic cell is the purity of its active parts. The zincs should be as near chemically pure as can be obtained; the peroxide of manganese of the best quality and perfectly free from foreign substances, and the sal ammoniac the purest that can be manufactured. The actual difference in work between a battery so constructed, and the average cheap cell sold at a price to catch the unwise, is tremendous. And this difference is indicated, not only in work, but when the battery is at rest. Local action in a cheap battery will exhaust it even when it is not in circuit, whereas a battery cell of good material will remain in good order for months without more attention than the addition of water or sal ammoniac. It has been often remarked that the batteries made to-day are inferior to those made years ago, but it is only true of the cheap-priced cells; if a good price is paid and attention given to securing a well made cell, the output will be as satisfactory.

[Ill.u.s.tration: FIG. 52.]

To set up a Leclanche cell, proceed as follows: Put six ounces of sal ammoniac into the gla.s.s jar; fill the jar one-third full of _clear_ water and stir. Put in the porous cup and fill the jar with water up to its neck, pouring a few teaspoonfuls of water into the hole in porous cup. When the cell is in working condition, the level of the solution will be found to have receded, owing to absorption by the porous cup. To prevent the creeping of sal ammoniac up the neck of jar and on to the terminals of the cell, a layer of paraffin is applied to neck of jar and porous cup. Should this need renewing, vaseline can be used, or any heavy grease, care being taken that it does not get on electrodes or where the wires are to be fastened. When the cell refuses to work, throw out old solution, wash porous cup, jar and zinc in warm water, and replace with new solution. There is a limit, when a new porous cup must be used, but this can be done when cell does not work after being treated as above. The electromotive force of the Leclanche cell is about 1.45, and current on short circuit of nearly one ampere, depending of course on thickness and porosity of porous cup, size of zinc, and a few other points.

THE SAMSON CELL.

Fig. 53 is one of the Leclanche group, in which a compound carbon element displaces the earthenware porous cup. This carbon is composed of two parts, a hollow-fluted lower piece and a threaded top, which carries the binding post. In the process of manufacture, the top piece is heated red-hot and plunged into hot paraffin wax, thus ensuring a complete diffusion of the paraffin throughout the carbon. In this way the creeping of salt or solution, and consequent corrosion of electrodes and failure of cell, are avoided. The lower portion is much more porous than the upper and is filled with a combination of pea-carbon and peroxide of manganese held in by a plug at the bottom.

This plug can be removed and new depolarizer added. Directions given by the manufacturers for renewing this element are to hold the lower end of the carbon over a burner flame until the plug is softened and can be removed, or to immerse the extreme lower end of the carbon in boiling water. After refilling, a cork plug can be used.

[Ill.u.s.tration: FIG. 53.]

The E. M. F. of the No. 2 size is from 1.40 to 1.47 volts, and current, on short circuit, of 12 to 16 amperes. The No. 2 Special has same E. M. F., but current of only 5 amperes, being intended where strong current is not required but quick recuperation. It will be seen that this cell is far more suited to electric gas-lighting work than the simple Leclanche, owing to its great current delivery.

THE DRY CELL.

Of so-called dry cells there are numbers on the market at so low a price that it does not pay to make one's own. But for those who wish to do so, the following formula, furnished by Mr. Wm. Roche, of New Standard battery fame, will be found excellent:

One pint CLEAR WATER.

Five ounces sal ammoniac.

Six ounces zinc chloride.

Dissolve the sal ammoniac in the water thoroughly. Let stand twenty-four hours. Then add the zinc chloride, and when cool, will be ready for use.

When you have your zinc cup ready, pour a little wax in the bottom, to insulate; place a piece of blotting-paper inside cup and laying tight against the zinc, about three turns. The negative element is prepared as follows: One pound pure carbon, powdered; one pound black oxide manganese; mix thoroughly. Then add sufficient of above solution to hold it together without being plastic, as that would be too wet to tamp.

Moisten your paper in the zinc cup thoroughly. Place your stick or plate of carbon in centre of zinc cup, hold it there central while you pack in the carbon manganese element all around it; be sure that carbon manganese, or negative element, does not touch zinc cup. If it does, your cell will run down quickly. It is a good precaution to have your paper half an inch higher than cup when in the cup, and soaked with the solution. Give it a couple of quick taps on the bench; that will curl the paper in at the bottom and insure against any internal short circuit. When your cell is filled up, clean all the carbon element away from the zinc. Seal, and your battery is ready when you've got the connections on.

[Ill.u.s.tration: FIG. 54.]

THE NEW STANDARD DRY CELL.

The princ.i.p.al sizes of this cell (Fig. 54) are as follows:

No. 2--5-7/8 2-7/16.

No. 3--3-3/4 1-7/8.

No. 5--6 2-9/16.

No. 6--6 3.

No. 7--7 3.

The electromotive force is 1.5 volts, current of the No. 7 size on short circuit, 24 amperes. Nos. 2, 5, 6, or 7 are most suitable for electric gas lighting, either by simple primary coil or jump spark coil.

THE EDISON LALANDE CELL.

This cell (Fig. 55), gives a large, steady current and is of low internal resistance, but its electromotive force is not high, being less than .7 volt on closed circuit. Its output of current varies with the size, type _S_ being .025 ohm internal resistance and capacity of 300 ampere-hours. The Edison Lalande cell can be applied to electric gas lighting in cases where a large demand is made upon the battery, for example in church or theatre lighting.

Its elements consist of positive plates of amalgamated zinc suspended on each side of negative plates of black oxide of copper. The electrolyte is an aqueous solution of caustic soda. A layer of heavy paraffin oil is poured on top of the solution to prevent the solution from evaporating and also to keep the soda crystals from creeping up and over the rim of the jar.

[Ill.u.s.tration: FIG. 55.]

To set up an Edison Lalande cell, fill the jar up to the brown mark with clear water; pour in the soda from the tin box, _and stir_. When thoroughly dissolved, pour on top of the solution one half-inch layer of _the oil which is sent with the battery_. Then the elements attached to the cover can be inserted, and the cell is ready for use.