The Electrical experimenter

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12 THE ELECTRICAL EXPERIMENTER May, 19 1 WJrllLt 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form of electricity is that which we see when we stroke pussy's fur in a dark room and obtain a spark when the hand is withdrawn from contact with the fur; or again, we may obtain the same form of electric shock or discharge by rubbing together two dissimilar substances, such as a stick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 pitli balls. A rapidly moving belt otten develops a considerable amount of static or frictional electricit}-, which will tend to discharge to earth whenever possible. One may often stand near such a belt, and by holding the knuckles or even liie ends of the fingers near the belt, a heavy static discharge will take place between the belt and the finsers, the electric charge passing thru the body to earth. One of the usual and practical sources of such electricity is the static machiiw (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 machme. 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 dissimiliar nietliods 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) whereas, the to chemical actions going on ; 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 much greater degree. tained by the contact and negative to a The voltage ob- between zinc and carbon The is 1.09 volts. 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 metil tends to dissolve into the liquid chemical. there will be an electro-motive force acting from the metal toward the liquid. .\ hot Sources of Electricity 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 o.xidizing 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 practise for ringing bells and operating medical coils in the form of the well-knov.-n 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 decompos" by the electro-chemical action taking place, and its consumption, in fact, furnishes Uie 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 tlie 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 wb.ile 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 be-ng 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 continuousl}- 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 Cases : 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 spongj- platinum. The glass bottle contains acidulated water in which the two glass tubes plunge, as seen. One of the tubes contains oxygen, the other hydro.gen, as will be noted the gases make contact wiih 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 heatin.g 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, .\mong 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 usuallj' 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 t'^sted bv lifting out the crystalline mass with a glass rod. Chocolate is another substance which manifests such an electrification while becomin.g solidified. Pie:o-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 shew-s\mmetry or hemihedry in their molecular structure. Thermo-electricity: If we take two metal bars, one cf bismuth and one of antimony, and join these togethe-, 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 couide. 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. (Continued on page 7r)
May, 19 1 THE ELECTRICAL EXPERIMENTER 13 SOURCES OF ELECTRICITY {For description see opposite page.)
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MURDOCK No. 55 SENSIBLY PRICED SENS
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The Electrical experimenter

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