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Sources of Electricity



While most of us are familiar possibly with several sources of electrical energy, we do not always stop to think of the many possible sources which are little known, especially to the layman. We have endeavored in the present article, and with the aid of the accompanying full page illustration, to describe the principal known sources of electricity.

Static Electricity: This form of electricity is that which we see when we stroke pussy's fur in a dark room and obtain a spark when the hand is withdrawn from contact with the fur; or again, we may obtain the same form of electric shock or discharge by rubbing together two dissimilar substances, such as a stick of sealing wax with a silk handkerchief, after which it will be found that the electrified stick of sealing wax will attract bits of paper or small pith balls. A rapidly moving belt often develops a considerable amount of static or frictional electricity, which will tend to discharge to earth whenever possible. One may often stand near such a belt, and by holding the knuckles or even the ends of the fingers near the belt, a heavy static discharge will take place between the belt and the fingers, the electric charge passing thru the body to earth.

One of the usual and practical sources of such electricity is the static machine (Fig. 1) and when the handle of such a machine is turned, one or more insulating discs are rapidly rotated, and by successive intensification of a very slight electric charge existing on the tin-foil sectors of these plates before the machine is started up, a surprisingly powerful static discharge is rapidly built up. This will manliest itself in the form of an electric spark, which crashes across the gap between two metal balls on the side of the machine. There are many other sources of static electricity but the whole phenomenon is practically the same.

Contact Electricity: It was Volta who showed that the contact of two dissimilar metals in the air produce opposite kinds of electrification, one becoming positively, and the other negatively electrified. There has been considerable discussion as to the exact action occuring in the production of electrical currents by the contact of two dissimilar methods in air, and for a long time, says Silvanus P. Thompson, the existence of this electrification by contact was denied, or rather it was declared to be due (when occurring in voltaic combinations) to chemical actions going on ; whereas, the real truth is that the electricity of contact and the chemical action are both due to transfers of electrons between the substances under the peculiar actions of forces, about which very little is known with certainty as yet.

Volta found that the difference of electric potential between the different pairs of metals was not all equal, as while zinc and lead were respectively positive and negative to a slight degree : zinc and silver proved to be positive and negative to a much greater degree. The voltage obtained by the contact between zinc and carbon is 1.09 volts.

The phenomena of electrical currents produced by the contact of dissimilar methods is illustrated by Fig. 2. A difference of potential or voltage is also produced by the contact of two dissimilar liquids. It has been found that a liquid and a metal in contact exhibit a difference of potential or voltage, and if the metal tends to dissolve into the liquid chemical. there will be an electro-motive force acting from the metal toward the liquid. A hot metal placed in contact with a cold piece of the same metal, also produces a difference of potential, and lastly Sir Joseph J. Thomson has demonstrated that the surface of contact between two non-conducting substances, such as sealing wax and glass, is the seat of a permanent difference of potential.

Galvanic Electricity: The primary battery is generally defined as one in which electrical energy is produced by chemical means, without having to charge the battery from dynamo or other source originally. The simplest form of such a battery comprises a glass or other vessel containing sulfuric acid and water, or any other oxidizing acid solution, and in which are immersed two clean metal strips, one of zinc and one of copper. Most of us are probably familiar with the common form of primary battery used in American practice for ringing bells and operating medical coils in the form of the well-known dry cell, or with the zinc-copper-salammoniac cell. In the zinc-copper-acid cell above mentioned, a continuous flow of electricity may take place thru a wire or apparatus which connects the two plates. When such a current passes, the zinc strip may be seen to waste away, or decompose by the electro-chemical action taking place, and its consumption, in fact, furnishes the energy required to drive the current thru the cell and the connecting wire or apparatus. In such a cell, the zinc strip forms the positive electrode or negative terminal, while the copper strip forms the negative electrode or positive terminal. Such a cell gives about one volt potential.

Fig. 3 shows a unique form of primary battery known as the Hauck Circulation; battery. In this battery, composed of several cells, the electrolyte or solution is caused to pass from a tank above the battery cells, thence thru the first or higher cell, then thru the next lower container, etc This is a chromic acid battery with carbon and zinc electrodes. The zincs are located in the rectangular porous cups while the two carbon plates are outside of the porous cups, all the space between porous cup and carbon plates, as well as between the carbon plates and glass vessel being filled out with small carbon pieces. In the porous cup there is a sulfuric acid electrolyte, while the carbons stand in chromic acid. As the latter is caused to circulate continuously- from one battery to the next, all polarisation is done away with and we obtain a very steady and powerful current. The battery illustrated gives 6 volts and 60 amperes and can be used to charge storage batteries, run fans, or electric lamps. It is one of the best chromic acid batteries ever designed.

Electricity from Gases: Fig. 4 shows the famous Grove Gas Battery invented in 1J59. It shows how two gases are used to produce an electric current. The two glass tubes contain platinum strips coated with spongy- platinum. The glass bottle contains acidulated water in which the two glass tubes plunge, as seen. One of the tubes contains oxygen, the other hydrogen, as will be noted the gases make contact with the acidulated water. If we connect the two terminals with a galvanometer we will observe an electric current, the oxygen furnishing the positive, the hydrogen the negative pole of the battery. Incidently we note that, as we consume current, the liquid rises in the two glass tubes, but twice as fast in the hydrogen tube as in the one containing the oxygen. .As each tube is identical with the other, except for the gases, it follows that the current can be due only to the gases. Also different gases produce different voltages and currents.

Pyro-Electricity or Electricity from Crystals: In the accompanying Fig. 5, we have several methods by which minute quantities of electricity are produced from crystals, when these are manipulated in a specific manner. Certain crystals, when they are heated or cooled, exhibit electrical charges at certain regions or poles, and such crystals which become electrified by heating or cooling are said to be pyro-electric. One of the principal crystals which manifest this peculiar action is tourmaline. The tourmaline has been cited in history, and is mentioned by Theophrastus and Pliny under the name of Lapis Lyncurius The tourmaline possesses the power of polarizing light, and is usually found in slightly irregular three-sided prisms which, when perfect, are pointed at both ends. It is interesting to note that in heating such a crystal as the tourmaline, it attracts light pith balls to its ends when electrified. If the temperature is kept steady, then no such electrical effects are observed either at high or low temperatures, and again the phenomenon ceases altogether if the crystal is warmed above ISO" C. If a heated crystal of tourmaline is suspended by a silk fiber, it will be attracted and repelled by electrified bodies or by a second heated tourmaline, Among other crystals which belong in the pyro-electric family are silicate of zinc, boracite, cane sugar, quartz, tartrate of potash and sulfate of quinine.

Electricity is produced by the disruption and cleavage of certain substances as for instance, when a sheet of mica is split apart, which action is usually accompanied by the production of a number of sparks, and both laminae are found to be electrified. If sulfur is fused in a glass dish and allowed to cool, it becomes powerfully electrified, which action may be tested by lifting out the crystalline mass with a glass rod. Chocolate is another substance which manifests such an electrification while becoming solidified.

Piezo-Electricity is the term given to that form of electrical energy produced when certain crystals are placed under pressure in a certain direction. With respect to the make-up of the crystal, it was found that if a crystal of calspar was prest between the fingers so as to compress it along the blunt edges of the crystal, that it becomes electrified, and retains its electrical charge for some days. This phenomenon is believed to be due in certain crystals to what is known technically as skew-symmetry or hemihedry in their molecular structure.

Thermo-Electricity: If we take two metal bars, one cf bismuth and one of antimony, and join these together, it will be found that an electric current is produced of an appreciable magnitude when the juncture between the metals is heated in the flame of a candle or other source of heat. To demonstrate that there is an electric current produced in all such cases, it is but necessary to connect a sensitive electric current-detecting device, such as a galvanometer to the free ends of the bismuth- antimony couple, as it is called. If all parts of the circuit, including all sections of the bismuth-antimony couple. are at one temperature, there will be no current produced, since the electro-motive forces are in perfect equilibrium. However, when a junction between two such metals is heated, this equilibrium of the electrons and molecules no longer exists, and gives way to the production of an E.M.F. or difference of potential.

As might be suspected, the voltage produced by heating a single metallic couple, such as the above, is very small, and where a greater potential is desired a large number of similar couples are mounted in as compact a manner as possible, and all of the junctions are heated simultaneously by gas or coal as shown in Fig. 6. The difference of potential for a bismuth-antimony couple is about 117 microvolts for each degree Centigrade, when the junction is heated above the rest of the circuit. The total current produced by the massive compound circular thermopile shown in Fig. 6 is 80 volts and 3 amperes, which is sufficient to light a number of incandescent lamps.

Dynamic Electricity: The most successful and practical source of electrical energy as we know it today is the Dynamo. One of these machines, which depends upon the cutting of magnetic lines of force by a rotating wire or inductor as it is called, is shown in Fig. 7. It was Faraday, who early in the 19tli century discovered that if a circular copper disc be rotated between the poles of a strong steel magnet or an electro-magnet, that there would be a current produced, or rather induced in the moving copper disc, due to the cutting of magnetic lines of force. The current was found to flow from the shaft supporting the disc to the rim, or vice versa, according to the direction of rotation. This current was conducted away by wires, having sliding brush contacts, one of which was made to bear against the shaft, while the other made contact with the edge of the disc.

It was not long before the simple copper disc gave way to the more modern armature, which contains a large number of insulated copper wires and all of which coils, in consequence, are caused to rotate rapidly in the powerful field of an electromagnet. These rotating coils are properly connected to a series of metal bars, assembled in ring form and known as a commutator, against which contact brushes bear, leading the current from the armature to the electric apparatus, such as lamps, motors, etc. The dynamo is always to be driven by some external prime mover, such as a steam engine, water wheel, etc. In the dynamo we have the conversion of mechanical energy into electrical energy.

Electricity From Coal: One of the most successful forms of apparatus for producing electricity direct from coal is shown in Fig. 8. This particular type of coal-electric cell is due to W. W. Jacques. Here we have a carbon cylinder immersed in a fused caustic soda bath; this is placed in an iron vessel which also serves as the other electrode of the cell. An air pump is employed to blow a stream of air thru the caustic soda by means of a perforated drum under the carbon rod. By means of the coal furnace the whole cell is maintained at a temperature of 400°C. The air stream has the effect of causing the carbon to oxidize to CO2, which mostly bubbles up thru the caustic soda solution and escapes. This cell gives about 1 volt E.M.F. The action occurring in the production of electrical energy is believed to be partly voltaic and thermo-electric. The cell has an efficiency of about 8 per cent—compared to 12 to 15 per cent for modern steam boiler and engine plants, and the cost of raw materials to replenish it is said to be at least 34 times that for a good steam engine, while the residue or ash from such a battery would possibly weigh 12 times that from a corresponding steam plant.

Plant Electricity: It is not generally known that certain plants exhibit pronounced electrical activity, but such is the case. Perhaps the strongest, that is in the sense of electrical vibrations, is the sensitive plant (Mimosa pud tea), shown in the illustration (Fig. 9). Others, such as iris, nicotiana, nasturtiums and practically all the meat-eating plants, such as the "Venus fly-trap" and the "sundew," afford splendid examples for experimentation. If any of these be placed "in connection with a galvanometer by means of electrodes attached to leaves on different sides, and one side of the plant be exposed to sunlight while the other side is kept shaded, then within from three to ten seconds after exposure to sunlight there will be a flow of electricity from the lighted to the shaded parts amounting to .005 to .02 volt. This continues for about five minutes, when the magnet begins to swing back and shows an opposite current of considerable magnitude. The manifestations are similar to those of "teranized nerve."

A better understanding of the electrical qualities of plants will, no doubt, explain many of the hitherto mysterious habits of meat-eating plants. Especially will this be true of such terrible and uncanny plant monsters as the "devil's snare" of South America and the mammoth Utricularia, or fishing plant, which lures minnows and small animals into its voracious mouth, and suddenly, as if an electric button were secretly prest, closes in upon its helpless prey. In other words, it fishes with a net electrically wired! Strange as it may sound this plant safeguarded itself by means of its electrical currents ages before we used the electric burglar alarm and door bell. Were it not for this protection, the plant could not live and hold its own in such an aurial-infested region as it needs for its fishing ground.

Animal Electricity: Altho not so commonly known, there are in the world several varieties of electric fishes and eels which possess, quite remarkable power. Several species of these creatures inhabiting the waters of certain parts of the earth possess the power of producing more or less powerful electric discharges. Physiologically, the principal creatures of this class are the Torpedo, the Gymnotus and the Silurus. One of the most powerful electric fishes is the Raia Torpedo or Electric Ray, of which there are three species inhabiting the Mediterranean and Atlantic. This particular specimen is provided with an electric organ on the back of its head. The organ consists of laminae composed of polygonal cells to the number of eight hundred or one thousand, or even more, which is supplied with four large bundle of nerve fibers. The under surface of this fish is negative: while the upper surface is positive. With the Gymnotus or Surinam eel, the electric organ extends the whole length of the body from tail to head. It has been recorded by Humboldt that a lively combat ensued between a number of electric eels and a herd of wild horses, which were driven by the natives unconsciously into the swamps inhabited by the Gymnotus. This particular specimen of electric fish is said to be able to give a most terrible shock, and proves a most formidable antagonist when it has grown to its full length of five to six feet. In the Silurus shown in our Fig. 10, the electric current Hows from head to tail.

It has been shown by several scientists that nerve excitations and muscular contractions of human beings are the seat of slight electrical currents. For one thing it has been shown that the beating of the heart really creates rhythmical electro-motive force.

Photo-Electricity: One of the most interesting sources of electrical energy and also one of the most direct methods of production of electro-motive forces is found in the photo-electric cell. Simply explained this remarkable device comprises nothing more than two copper plates, one of which is perforated and blackened by oxidizing in a gas flame, while the rear or second plate is polished, and both of which plates are placed in a suitable tank containing a salt-water solution. One side of the tank which contains the copper plates is lifted with a glass window and when sunlight, or any other source of light, is allowed to strike the cell, there is a difference of electric potential set up between the front and rear copper plates. This particular cell as developed by Mr. Theodore W. Case, was described extensively in an article which appeared in the September, 1916, number of this journal. It was found possible with some of these photo-electric cells to obtain a voltage of one-tenth and an amperage of two-tenths ; the cell delivering a steady current as long as the light shown on it. It is of course possible to connect a large number of cells in series or parallel to obtain any voltage or current desired.

Radium Electricity: It is generally conceded in scientific circles that the activity possest by radium is fundamentally electrical in nature. Radium gives off three kinds of rays known as the alpha, beta and gamma rays. It is possible to influence two of these rays (alpha and beta rays) by means of a magnet or an electro-magnetic field, which indicates that they are undoubtedly electrical in their fundamental structure. Another experiment, which any schoolboy can readily perform with a piece of radio-active mineral, is as follows: First, an electric charge is produced on a sensitive gold leaf electroscope, so that the leaves diverge; then grasp a piece of the radioactive mineral (some may be so fortunate as to possess a tube containing a small quantity of radium bromid and bring this into proximity with the metal ball or disc at the top of a charged electroscope. It will be noted that the latter loses its charge on the gold leaves almost instantly; the electronic activity of the radium bromid or other radio-active substance used creating a change in the electrical field about the electroscope, apparently making it more conductive, so that the bound electric charge on the gold leaves can escape. Those interested in the subject of "Radium" and the many electrical and other effects created by the greatest mystery of the scientific world to-day will do well to read the extensive article on this subject, which appeared in the September, 1916, number of The Electrical Experimenter.


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