Simple Galvanic Circuit.--- If two plates of different metals, such as copper and
zinc for example, are immersed in a vessel of water to which a small portion of sulphuric
acid has been added, and the upper ends of the two plates are brought into contact, or
connected together with a metallic wire as in fig. 1, a continuous current of electricity
will pass from the copper to the zinc through the connecting wire, and from the zinc to
the copper through the liquid, as indicated by the arrows in the figure. If the metallic
communication be interrupted, or the circuit, as it is termed, broken, the current
at once ceases, but is instantly renewed whenever the connection is again formed.
Electricity produced by this means is usually termed Galvanic or Voltaic electricity, from
the names of its discoverers, and is the effect of chemical action by the acidulated water
upon the zinc.
2. The plate (usually of zinc), upon the surface of which the electricity is generated by chemical action, is called the negative pole, and the opposite plate, generally of copper, platina or carbon, is called the positive pole. They are also frequently designated by the signs - (minus) and + (plus).
3. If both metals in this arrangement were equally acted upon by the solution, no electricity would be produced, as this effect arises in all cases from the difference in the chemical action upon the two plates. For this reason the positive plate is made of some metal or other substance upon which the liquid has little or no effect.
4. The apparatus for producing voltaic electricity, which has been described in its simplest form, is called a battery. As electricity is produced under any circumstances in which the above conditions have been complied with, there are various methods of constructing a battery. The forms used in the practical operation of the telegraph will hereafter be described in detail.
5. Conductors and Non-Conductors.--- Some substances, such as metals, possess the property of allowing electricity to diffuse itself freely throughout their whole substance, and are therefore termed conductors. Others, such as glass, hard rubber, and dry wood, offer great resistance or opposition to this diffusion, and are called non-conductors or insulators.
6. This division however is relative and not absolute. Few if any bodies are perfect insulators, and even metals, the most perfect of all conductors, offer some resistance to the passage of electricity, or in other words insulate slightly. A good insulator, therefore, is simply a bad conductor, and vice versa.
7. In the following list each substance named conducts better than that which precedes it, the first being the best insulator and the last the best conductor:
8. Electrical Tension.--- If two or more simple batteries, or elements as they are called, are connected together in such a manner that the positive plate of the first is united by a metallic conductor with the negative plate of the second, and so on, as shown in fig. 2, the electrical tension, or power of overcoming resistance, is increased in direct proportion to the number of elements. Four elements will therefore possess four times the tension of one element, and the current generated by their combined action will be capable of overcoming four times the resistance of that from a single element.
9. Electrical Quantity.--- It is important, however, to observe, that although the tension increases with each element added to the series, no greater quantity is produced by a great number of elements than by a single one---the action in each cell serving only, as it were, to urge forward a quantity equal to that arising from chemical decomposition in the first cell. If, on the contrary, we connect together the four zincs and the four coppers, forming in effect a single element, with plates equivalent to four times the original surface, there will be four times the original quantity of electricity generated ; but its tension, or power of overcoming resistance, will be no greater than that of a single pair of plates. This distinction is of great importance, and should be thoroughly understood and carefully remembered.
10. In the simple form of battery previously described (8), if the poles are united by a conductor for a considerable length of time, bubbles of hydrogen, arising from the decomposition of the water, cover the positive plate, and in a great measure prevent the liquid from coming in contact with it, and the surface of the plate also becomes coated with a deposit of zinc, tending to convert the battery into one in which both plates are of zinc, and thus its electro-motive force is weakened and finally destroyed. In order to render the battery constant in its action, it is necessary to prevent these effects by surrounding the negative plate with a solution of a salt of the metal itself. This principle is employed in the arrangement about to be described.
11. The Daniell Battery.--- This combination consists of a jar of glass or earthenware, F (fig. 3), about six inches in diameter and eight or nine inches high. A plate of copper, G, is bent into a cylindrical form, so as to fit within it, and is provided with a perforated chamber, to contain a supply of sulphate of copper in crystals, and a strap of the same metal with a clamp for connecting it to the zinc of the next element. H is a porous cup, as it is technically termed, made of unglazed earthenware, six or seven inches high and two inches in diameter, within which is placed the zinc, X. This is usually of the shape shown in the figure, which is called the ``star zinc,'' but it is often made in the form of a hollow cylinder, the latter giving greater power, but being somewhat more difficult to clean.
The outer cell is filled with a saturated solution of sulphate of copper (blue vitriol), and the porous cell with a solution of sulphate of zinc. A series of three elements connected together, as usually employed on American lines for a local battery, is shown at I.
12. Effect of Continued Action.--- By continued action sulphate of zinc is formed in the porous cup, and the sulphate of copper in the outer cell consumed, the zinc being constantly dissolved away while the copper plate is at the same time increased. When all the sulphate of copper has been decomposed, and the water in the zinc compartment saturated with sulphate of zinc, the action of the battery ceases. Some of the sulphate of zinc in this case usually passes into the copper cell, and appears upon the copper plate in the form of a black powder ; it is therefore necessary to maintain a constant supply of pulverized vitriol in the perforated chamber attached to the copper cylinder.
13. When the solution in the porous cup becomes saturated with sulphate of zinc it crystallizes upon the zinc plate, interfering with the action of the battery. Part of this solution should therefore be removed occasionally and replaced with water.
In setting up the battery pure water may be used in the porous cell, and the battery allowed to stand a few hours with a closed circuit, when it will be found ready for use. The addition of a little sulphate of zinc will greatly hasten its action.
14. The Deposit of Copper upon the Porous Cup.--- This cannot be entirely prevented, but may be greatly lessened by suspending the zinc so that it will not touch the porous cup below the surface of the liquid, and by saturating the bottom of the cell to the height of half an inch with melted paraffine, or even tallow.
15. When constructed as above described and used in a local circuit, the Daniell battery will continue in action about ten or fifteen days without attention, the time depending upon the size of the wire in the magnet and the amount of daily service. The sulphate of copper solution should be kept of good strength, otherwise the upper portion becomes weak and an extra current is set up within the battery, which tends to eat away and destroy the copper plate without any useful effect.
16. Renewal of the Battery.--- In renewing this battery the zincs should be scraped and well cleaned with a stiff brush, the porous cups thoroughly washed, and the old solution contained in them thrown out, with the exception of about one third of the clear portion, which should be returned, otherwise the battery will require some hours to recover its full strength. The copper deposit upon the zincs is valuable, and should be preserved.
Every two or three months the coppers ought to be taken out and the deposit upon their surface removed, which may be done two or three times. When they become too much encrusted to afford room for the porous cups they must be replaced by new ones.
Porous cups ought to be renewed whenever they become too much encrusted with copper. If cracked they should be changed at once, otherwise a great waste of material will ensue.
17. The crystals which form around the edge of the outer jar require to be occasionally wiped off with a damp cloth, or they will eventually run down the outside and form a connection between the jars, giving rise to a great consumption of material without corresponding benefit.
18. In order that the current may act with its full force, it is necessary to keep the clamps and connections of the battery clean and bright, and free from rust or dirt. As chemical action is promoted by heat, the battery will act more vigorously if kept in a warm place.
19. Application of the Daniell Battery to Main Circuits.--- This battery is sometimes used for main circuits, but in that case it is preferable to arrange it differently by placing the zincs outside and the copper within the porous cell, as in fig. 4, in which Z shows the zinc and P the porous cell. The copper, C, is provided with a perforated shelf, D, upon which the vitriol is placed.
Other forms have been devised which dispense entirely with the porous cup, the two solutions being separated by the difference in their respective specific gravities. Some of these bid fair to come into extensive use.
20. The Grove Battery.--- The most intense and powerful voltaic combination that has yet been discovered is that of Grove. For many years it was exclusively used for telegraphic purposes in this country, and is still employed in that capacity to a considerable extent. Its component parts are shown in fig. 5, in which A represents a glass jar or tumbler, about 3 inches in diameter and 4 1/2 inches high. A thick cylinder of zinc, B, of a size nearly sufficient to fill the tumbler, is placed within it, and is furnished with a projecting arm, to which is attached the positive plate of the next element. The porous cup, C, is placed within the zinc. A thin strip of platina, D, about 2 1/2 inches long and half an inch in width, is soldered to the end of the zinc arm projecting from the adjacent cell, and reaches nearly to the bottom of the porous cup.
21. Setting up a Grove Battery.--- It is necessary that the zinc should first be thoroughly amalgamated. The ordinary zinc of commerce contains particles of lead, iron, and other impurities, which, when the plate is immersed in dilute acid, form as it were small batteries upon the surface, which eat away numerous cavities in the zinc without producing any useful effect. This is prevented by the above process of amalgamation, which is usually performed by immersing the zincs in a vessel containing dilute muriatic or sulphuric acid, and then plunging them in a bath of metallic mercury. After remaining in this for a minute or two they are taken out and placed in a vat of clean water, where the superfluous mercury is allowed to drain off. The mercury dissolves a little of the zinc, which flows over and covers the impurities, and prevents the acid solution from coming in contact with them.
22. In putting the Grove battery together, first place the glass tumblers in position and fill them about half full of a solution composed of one part of sulphuric acid and twenty to thirty parts water, by measure, thoroughly mixed. Then place the amalgamated zincs in the tumblers, with the arms turned at right angles to the line of cells. Fill the porous cups nearly full of strong nitric acid and place them within the zincs, then turn the zincs around so as to immerse the platina strips in the nitric acid of the adjoining cell, throughout the whole series, as shown at T, in fig. 5.
23. The strength of the dilute sulphuric acid solution in this battery should be varied in proportion to the number of wires worked from it. The less the number of the latter the weaker the solution may be made.
24. When in continuous service a Grove battery ought to be taken apart every night, and the nitric acid from the porous cups emptied into a vessel and kept closed until morning. The zincs should be removed and placed inverted in a trough of water, acidulated with sulphuric acid, and in the morning rubbed with a brush, and the mercury diffused evenly over their surfaces. To every ten parts of the nitric acid taken from the battery add one part of fresh acid every morning. By this means a steady and uniform current will be maintained when the battery is in action. The dilute sulphuric acid requires renewal about twice a week. In handling this battery great care is required not to injure the connection between the zinc and the platina. A set of Grove zincs, in continuous service, will require renewal about once in three months.
25. The Carbon Battery.--- This is a modification of the Grove battery, and is sometimes called the Electropoion battery. It is extensively employed on the American lines for main circuits. In its general construction and arrangement it differs but little from the battery last described. The different parts of which it is composed are shown in fig. 6, consisting of a glass tumbler, zinc and porous cup. In place of the platina of the Grove battery, a plate of carbon or coke is employed for the positive element, as shown in the figure. A clamp is arranged so as to press a platina button firmly against the carbon, this button being permanently attached to a wire leading to a binding screw on the zinc arm of the next element. The parts are usually made of about the same size as in the Grove battery.
The carbon connection is sometimes made by means of a platinized copper wire inserted into its upper end, and surrounded with lead, to prevent the action of the acids upon the copper.
26. In setting up this battery the different parts should be put together in the position they are to occupy, as shown in fig. 6, and care taken that all the connections are firmly screwed up. The zincs must be thoroughly amalgamated, and the dilute sulphuric acid solutions mixed as directed for the Grove battery. A sufficient quantity of this solution is poured into the tumblers to cover the cylindrical portion of the zincs. The porous cups are then filled with a solution of bichromate of potash,* care being taken not to pour it upon the connections or clamps.
* This solution is made as follows: Mix one gallon of sulphuric acid and three gallons of water. Then, in a separate vessel, dissolve five lbs. bi-chromate of potash in two gallons of boiling water and add to the above, mixing the whole thoroughly together. The proportion of bi-chromate is sometimes made one fifth greater than the amount given.
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27. When the battery is in service, one third of the bi-chromate solution in the porous cups should be removed every morning by means of a large rubber syringe, and replaced with fresh. A new set of zincs will require to be amalgamated a second time after having been in use three of four days ; after which once in two to four weeks will be often enough---depending somewhat upon the amount of work required from the battery. The battery ought to be taken apart every two weeks, the zincs brushed, the dilute sulphuric acid solution renewed, and the carbons thoroughly soaked in clean water. It is better, if possible, to have a spare set of cells complete, so that one may be renewed while the other is in use.
28. Power of the Carbon Battery.--- This is quite equal to that of the Grove, as far as the intensity of its action is concerned. The latter however will work nearly twice as many wires at the same time as the former. The expense of the carbon battery for materials and attendance is less than one third that of the Grove. A set of zincs, if properly cared for, will last from fourteen to sixteen months on an ordinary telegraph line. It is a good plan to coat the zincs with asphaltum varnish at the junction of the projecting arm, as these are frequently eaten off while the rest of the zinc remains in good condition.
29. Insulation of Batteries.--- The cells of a battery should always be thoroughly insulated from each other. This is especially important in the case of the Grove battery. A convenient and effective mode of insulation is shown in fig. 7, in which the battery tumblers, AA, are set upon hollow cylinders of wood, BB, saturated with asphaltum or paraffine, and insulated from the upright wooden pins, DD, by the glass sockets, CC. The pins are inserted into a horizontal scantling, E, which forms the top of the battery stand.
Battery jars, of different sizes are now made at the Brooks Paraffine Insulator Works,
in Philadelphia, which are composed of stone-ware, thoroughly saturated with paraffine, so
that moisture will not penetrate them, nor remain upon their surface. When these jars are
employed, no special insulation is required.