« PreviousContinue »
200. Mr. Singer in the following experiment wires of which, C, C, are directed against the has availed himself of the discovery of Cavallo, foats of the wheel. who observed that some mineral colors are affected by passing over them the electrical dis
EXPANSIVE Power Of The Fluid. charge. Color, says he, both sides of a card 203. The influence of the electric matter in with vermilion, and place it upon the table of expanding bodies through which it is sent, may Henley's discharger; one of the wires should be clearly illustrated by these experiments. be beneath the card, and the other in contact Place a small card, or the cover of a book, with its upper surface; the distance of the points against the outer coating of a charged jar, exof the wires being one inch. If a charge be posing about a square foot of coated surface; now sent through the wires, the Auid will pass put one end of the discharging rod against the from the positive wire across the surface of the card, and bring the other to the knob of the jar; card to the part over the negative wire, and will the charge will pass through the card and perthere perforate the card in its passage to that forate producing a small bur on the side next wire. "The course of the fluid is indicated by a the discharging rod, and a larger one on the side black line on the card, reaching from the point which was in contact with the coating of the jar. of the positive wire to the perforation ; and by In the same manner, by using the more powerful a ditiused black mark on the opposite side of charge of a battery, a perforation may be made the card around it, and next the negative wire. through a quire of paper or a thin unbound book; These effects are pretty constant, the black line and, if either of these be freely suspended between always appearing on the side of the card which the balls of the universal discharger, no motion is in contact with the positive wire, and the per- of the paper will be produced, but the charge foration being near the negative wire.
will pass through it without in the least disturb201. But the most satisfactory exhibition of ing it, for the same reason that a musket ball the course of the fluid from the positive to the will pass through a door without causing it to Degative conductor is afforded in the next ex turn on its hinges, although, under the same cirperiment, which was the contrivance of Mr. cumstances, a very slight force would be sufficient Singer, and which he himself considered as re to move it. moving all difficulties on the subject. It has, 204. The effects produced on the card in the observes he, been long known that a light float- preceding experiment, as well as some others wheel
, made by inserting several vanes of card that have resulted when the experiment has been in the periphery of a cork that is made to turn varied, have led some electricians suppose freely on a pin or centre, will be put in motion that they might be viewed as indications of the by presenting it to an electrified point; and the course of the electric matter, and as affording motion of the wheel being always froin the point, no obscure proof of the existence of two fuids; Whether that point was positive or negative, has but Mr. Singer has, in our opinion, satisfactorily been occasionally urged as an argument for a shown that they are produced solely by an exdouble current of the fluid ; although it is evi- pansion of the paper. dent, from what has been already stated, that a 205. The following illustration of this inpoint either positive cr negative must produce a fluence is attributed to Mr. Lane, the inventor current, by the recession of the air opposed to it of the discharging electrometer. Roll up a piece when similarly electrified, by its contact, which of soft pipe-clay, in the form of a small cylinder, is fully adequate to the production of these ef- and insert in it two wires, so that their ends, fects
. Conjecturing that the currents of electri- without the clay, may be about one-fifth of an hed air would not take place in this manner if inch from one another. If a charge be sent the points were opposed to each other, the fol- through this clay, by connecting one of the wires lowing arrangement was made.
with the outside of a jar, and the other with the 202. A light float-wheel of the above descrip- inside, it will be inflated by the shock passing tion, being mounted so as to turn freely between between the two wires, and, after the explosion, two upright wires, was placed on an insulated will appear swelled in the middle. If the charge stem, and introduced between the pointed wires sent through it is too strong, and the clay not of Henley's discharger, which were placed ac very moist, it will be broken by the explosion, curately opposite to each other, and at the dis- and the fragments scattered in every direction. tance of rather better than an inch from the To make this experiment with a little variation, upper vanes of their respective sides. On con- take a piece of the tube of a tobacco-pipe, about Decting one of the wires with the positive con one inch long, and fill its bore with moist clay ; ductor of the machine, and the other with the then insert in it two wires, as in the above rolled negative conductor, and turning the machine, clay, and send a charge through it. This tube the wheel will move in a direction from the will be burst by the force of the explosion, and positive to the negative wire. On reversing the its fragments will be scattered about to a great connexions, so that the wire which was negative distance. If, instead of clay, the above-menmay become positive, sad that which was posi- tioned tube of the tobacco-pipe, or a glass tube, tive be made negative the motion of the wheel which will answer as well, be filled with any will be reversed; for it will still move from the other substance, either electric or non-electric, positive to the negative wire, thus proving that inferior to metal, on making the discharge it will the electricity moves in that direction. A re- be broken to pieces with nearly the same foice. presentation of this wheel, with the method of 206. The expansion of Auids by electricity is using it, is given in fig. 3, where A is the float- truly remarkable, and often productive of some wheel placed on the universal discharger B, the singular results. When the charge is strong, no
glass vessel can resist its force, Beccaria placed That this contraction arose from expansion apa drop of water between two wires in the centre peared from the wire having increased in thickof 3. solid glass ball of two inches in diameter; ness whilst it was diminished in length. on passing a shock through the water the ball was dispersed with great violence. Mr. Morgan
Solid BODIES RUPTURED BY ELECTRICITY. succeeded, by the same means, in breaking 212. The simplest form, perhaps, in which green glass bottles, filled with water, when the this can be done, is to place on the table of distance between the wires that conveyed the Henley's discharger a piece of dry writing-paper, spark and the sides of the glass was upwards of and pass over it, by means of the pointed wires, two inches.
a powerful charge from a large jar; if the wires 207. A single spark may be made to perforate be placed at about two inches asunder, and so a strong glass tube by the following simple as to touch the ends of the paper, it will be torn process : fill a small phial with olive oil, and in- in pieces. If, instead of the paper, a number of sert into it a pointed wire bent at right angles, wafers be placed in the circuit, they will be cuso that by sliding through a cork fixed in the riously dispersed, and many of them broken to neck of the phial, the point of the wire may rest pieces. against any part of the inside beneath the oil: 213. Make two small holes in the opposite attach the phial by its wire to the conductor of ends of a piece of oak, of about half an inch the machine, and bring the knuckle or a brass long and a quarter of an inch thick; introduce ball near the outside of the phial, opposite to two wires into the holes, so that their extremities the point of the wire within it; a spark will within the wood may be rather less than a quarter pass from the point to the knuckle, and make of an inch distant; on passing a strong charge small hole in the glass. By varying the situation from one wire to another, the wood will be split. of the point, many such perforations may be Several other substances that are imperfect conmade in the glass.
ductors, such as loaf-sugar, marble, &c., undergo 208. Of this very singular experiment Mr. similar injuries, when introduced into an elecSinger offers the following rational account. trical circuit; and even the hardest bodies, The point, he says, serves as an internal coating and the most perfect non-conductors, such as to a very small portion of the glass; and the glass, are perforated or broken by a strong charge being prevented from extending, by the charge. surrounding oil, the whole power of the machine 214. Lay a piece of plate-glass of about an is concentrated in that point, and consequently inch square, and half an inch thick, on the table soon overcomes its resistance. Similar effects of the universal discharger, or screw it very will always result when a large quantity of elec- tightly within the press of the same; set the tricity is guddenly transferred to a comparatively prints of the sliding wires opposite to each other, limited surface.
and against the under surface of the glass, so 209. Make a small mortar of ivory, with a that the charge may pass along that surface. If cavity of half an inch diameter and an inch now a strong charge be passed in this way, the deep; insert two wires through the sides of the glass will be broken into small fragments, and mortar, so that their points within the cavity some of it reduced to an impalpable powder. may be separated by an interval of of an inch; 215. The following experiment affords a fit a cork cap so as to close the aperture as ac- beautiful, though rather an expensive, illustration curately as possible without friction : when a of the same principle. Charge a very large jar, strong charge is passed through the wires, the and connect its external coating with that of one air within the mortar will be suddenly expanded, ten or twelve times smaller ; form a communiand the cork projected to a distance with some cation between their internal coatings by the violence.
discharging rod, and the small jar will be broken 210. Satisfactory and striking as the preceding in pieces, by the strength of the quantity of experiments are, they appear inferior to the electricity thus suddenly transferred to it. following: in making experiments on the effects of explosions of electricity sent through metallic
INFLAMMABLE SUBSTANCES KINDLED BY
ELECTRICITY. bodies, Dr. Priestley found that a chain which he had used as the medium of conveying the charge 216. Almost all inflammable substances may was shorter after being used than it was before. be kindled by means of electricity, but those geThis led him to try the effect of a strong charge nerally selected for the purpose of experiment on a definite length of chain : the charge was are resin, gunpowder, rectified spirit of wine, sent from sixty-four square feet of coated surface, ether, and hydrogen gas. through twenty-eight inches of chain, which, on 217. The common method of kindling resin being measured again, was found to be con- by the electric spark is to pulverise it, and dust tracted a quarter of an inch in its whole length. the powder on some dry cotton wool. Thus, if
211. This experiment was repeated by Mr. a small quantity of flax, or of cotton wool, be Naime with a piece of hard-drawn iron wire loosely tied on one of the knobs of the disten inches in length, and Ido of an inch in di- charging rod, and a little finely-powdered resin ameter. Through this wire he discharged twenty- dusted on it, and a jar be discharged by bringing six feet of coated surface nine times; after the the end of the rod thus prepared in contact with sixth and the ninth time the wire was measured, the knob of the jar, the charge will pass through and it was found to be shortened to of an inch the fax, or wool, and in so doing will melt and after each discharge. farther discharges sent ignite the resin, and set the whole on fire. A through it, the wire was shortened 17th inch. very neat contrivance for giving this experiment
a better effect is represented by fig. 4. A is a his finger, he may fire the spirit with a piece of mahogany board, six inches in length, three in ice, when the experiment will seem much more breadth, and half an inch in thickness. B is a surprising. If the spoon is held by the person glass pillar fixed in the middle of A, and sup- standing upon the floor, and the insulated person porting a piece of wood C, which is three inches brings some conducting substance over the surlong, an inch and a half broad, and about three face of the spirit, the experiment succeeds quarters of an inch thick. In each end of this equally well. This experiment is sometimes piece there is a small screw-ring: the extremities rendered still more striking in the following of these screws just touch a wire proceeding to manner : near the prime conductor of the maeach of them from two small brass knobs in- chine, place on the table three wine glasses ; serted at the ends of a shallow groove on the connect the first glass with the conductor by a upper side of C; these rings serve to hook the brass chain, which will reach to the bottom of chains on when the instrument is used. On the it; and with it let the second and third be conback part of C stands the perpendicular piece D, nected by a piece of fine brass wire, bent in the in the top of which is fixed the brass pin E. To form of the letter A. Fill the first and second use this for the purpose of igniting resin, it is glasses with water, and into the third pour a only necessary to dust the cotton with powdered little ether; turn the machine, and with a wire, resin, and hang it on the pin E, letting the having a small ball affixed to it, draw a spark lower part of it reach down to the piece C. from the ether, and it will be immediately inConnect one end of C with the inside of a jar flamed. In this experiment the electric fluid and the other end with the outside; discharge had to pass through two distinct portions of the jar, and the fluid in passing between the two water before it could come to the ether. small brass knobs will inflame the resin and 221. Hydrogen gas is generally inflamed by kindle the cotton.
the electric spark in the following manner : take 218. But the inflammation of resin is rendered a brass cannon, such as is represented in fig. 5, still more striking by the following experiment: and charge it with hydrogen gas by holding the let a flat porcelain dish be filled with water, and mouth of it for about half a minute over a stone on the surface of the water strew a quantity of or glass bottle in which the gas is generated, finely powdered resin; place two wires at the and then fix the cork tightly into the mouth of opposite sides of the dish, having their ends the cannon. The person who is to discharge it near the surface of the water, and at about the must now stand on the insulating stool, and, distance of four inches from each other. Pass holding in his hand a chain attached
the prime the charge of a large jar through this circuit, and conductor, must, with a wire and ball held in the resin which forms a part of it will be beau- the other hand, communicate a spark to the knob tifully inflamed.
of the cannon: this spark will pass into the in219. The firing of gunpowder by the electrical terior of the cannon through the glass tube B, explosion requires considerably more care and and the gas will instantly explode with a loud address than the firing of resin. It may, how- report, and the cork will be driven out to a conever, be effected by the following method: take siderable distance. This experiment may be either a large goose-quill or a small cartridge of rendered more effectual by mixing about onepaper, and fill it with gunpowder ground very third of oxygen with the hydrogen gas; or, if fine ; into this insert two wires, one at each ex- oxygen cannot be conveniently procured at the tremity, so that their ends within the quill or car- time, the operator may easily contrive to have tridge may be about one-fifth of an inch from some atmospheric air in the cannon, which will each other: this done, send the charge of a phial render the hydrogen gas more explosive. through the wires; and the spark between their 222. The very great ease with which inflamextremities, that are within the cartridge, or mable air is kindled by even a small spark of quill, will inflame the gunpowder. If the electricity seems to have suggested to M. Volta gunpowder be mixed with steel-filings, it will the idea of what he calls his inflammable airtake fire more readily, and with a very small lamp, an instrument which appears to have laid charge.
the foundation for the patent apparatus for ob220. Rectified spirit of wine, or ether, may be taining instantaneous light. This curious instruthus inflamed by a single spark from the con ment is represented in fig. 6, where A is a glass ductor of the machine when in action : hang to globe for containing hydrogen gas; B a glass the prime conductor a short rod having a small reservoir for holding water; and D a stop-coek, knob at its end; then pour some spirit of wine, by which a communication is formed between a little warmed, into a metallic spoon; hold the the water and the gas. The water passes into spoon by the handle, and place it so that the the globe through the pipe yg, which is fixed small knob on the rod may be about one inch into the top of the reservoir A; at s there is a above the surface of the spirit. In this situation, cock to cut off or open a communication between if a spark be taken from the knob, it will set the the air and the jar K. N is a contrivance for spirit on fire. This experiment may be varied holding a wax-taper; L a brass pillar, on the and rendered very agreeable to a company of top of which is fixed a ball of the same metal; spectators. A person standing upon the insu- ais a pillar of glass, with a socket at the top, lating stool, and communicating with the prime in which the wire b slides, having a ball screwed conductor, may hold the spoon with the spirit in on the end of it. F is a cock by which the his hand, and another person standing upon the globe is filled with hydrogen gas, and which floor may set the spirit on fire by bringing his afterwards serves to confine it, and what water finger within a small distance of it. Instead of falls into B and A. To use this instrunent,
having filled the globe with gas, and the reser 226. This may be rendered very obvious by voir A with water, turn the cocks D and s, and the following experiment:-Charge a large jar, the water will fall into the globe, forcing up and place a smooth piece of coin between the a quantity of gas, which will rise through the knob of the discharger and the coating of the pipe K. 'If
, now, an electric spark be made to jar; when the discharge has been made, the pass from the ball m to that marked n, it will set piece of coin will be found slightly adhering fire to the gas which passes through the pipe K. to the tin-foil, by its fusion at the point of conTo extinguish the lamp, first shut the cock s, tact, and will remain so as to require some force and then D. The gas is obtained in the usual to separate them. way, from diluted sulphuric acid and iron fil 227. Dr. Franklin's experiments on the fusing ings; and the globe is to be filled in the follow- of metals may be thus imitated :—Take three ing manner:-Having previously filled it with pieces of window-glass, each one inch wide, and water, place the foot R in a vessel of water, so three inches long, and place them contiguous that it
may be covered, and the bent glass tube, to each other, with two narrow strips of goldthrough which the gas is to be introduced, may leaf between them, so that the middle glass may pass commodiously below the foot. When the have, on each side of it, a strip of gold, with gas has displaced nearly all the water, turn the its ends projecting a little beyond the glass. cock F, and the lamp is ready for use.
Let the whole be properly secured within the 223. This instrument is sometimes constructed press of the universal discharger; pass the charge so as to be connected with an electrophorus for of a large jar through the strips of gold, they the purpose of producing a light at pleasure. In will be melted and driven into the glass. The this case the electrophorus is placed in a box outer pieces of glass are generally broken, but beneath the vessel containing the hydrogen gas; the middle piece is often left entire, and is from this box a wire passes through a glass tube marked with an indelible metallic stain on each to the opening of the stop-cock. The cover of of its surfaces. the electrophorus must be connected by a silk 228. The colors produced when metals are string with the handle of the stop-cock, so that thus fused, either on glass or paper, are soinethe same motion that opens the cock, may raise times exceedingly beautiful, and have been in the cover of the electrophorus, and the spark some cases employed in impressing letters, and that strikes from it be conveyed by the insulated ornaments of various kinds, on silk and paper. wire to the stream of gas, which it inflames. The process observed in such cases, Mr. Singer This effect will take place every time the stop- thus describes in his Elements :— The outline cock is opened, for the electrophorus will pro- of the required. figure is first traced on thick duce sparks for a considerable time, without any drawing paper, and afterwards cut out in the fresh excitation; and the quantity of gas con manner of stencil plates. The drawing paper sumed at each repetition of the process is very is then placed on the silk or paper intended to small, so that a light may be obtained above a be marked; a leaf of gold is laid upon it, and hundred times before the contents of the reser a card over that; the whole is then placed in a voir are expended ; and it may then be easily press, or under a weight, and a charge from a replenished!
battery sent through the gold leaf. The stain is 224. But by far the most remarkable effects confined, by the interposition of the drawing of electricity in producing combustion, result paper, to the limit of the design; and in this way from its action on metallic substances. This a profile, a flower, or any other outline figure property of the electric matter seems to have may be very neatly impressed.' been first observed by the celebrated Dr. Frank 229. In describing Cuthbertson's electromelin, who made several experiments on the sub- ter, No. 177, we made some remarks on the ject. These experiments were repeated and ex. fusing of wire, by passing through it the distended by Mr. Kinnersly, and also by Beccaria; charge of accumulated electricity; it may be and have since then been prosecuted with great necessary to offer bere some general observaaccuracy by Mr. Brook, Dr. Van Marum, Mr. tions on the same subject; and to give some Cuthbertson, Mr. Singer, and others. In treat account of the results of the experiments made ing on this part of the subject, we shall, as in by those whose names we have already enuthe preceding instances, give a course of pro
merated. gressive experiments, which may be made with 230 For the fusing of wires of different lengths an appropriate apparatus, from a single jar of a very large batteries were formerly considered as tolerably large size, up to a powerful battery, indispensable; but Mr. Singer observes, that, if previously remarking that the whole of the ap- the wire be sufficiently fine, a single jar, exposparatus must be in the very best state in which ing a coated surface of about 190 square inches, it can be put, otherwise disappointment, in many will be sufficient to afford an example of the cases, and inaccuracy in all, will be the result. effect. The finest flattened steel wire, sold at
225. The slightest indication of the fusing of the watchmakers' tool shops under the name of metallic substances is observed in the discharge pendulum wire, is the best for the purpose; harpof the Leyden phial: on this occasion, if the sichord wire not being fine enough, excepting discharge be made by means of the common where great power is used. Cuthbertson's discharging rod, the knob that touches the out Balance Electrometer should be invariably used side coating will be found to adhere slightly to to regulate the charge; the circuit made as short the jar after the discharge; and this arises from as possible; and the wire to be fused placed in the fusing of a small portion of the tin-foil a straight line, and held at the ends between coating.
a small forceps made of wire.
231. The following is the substance of Mr. obtained in all comparative experiments; and, as Singer's remarks on the numerous experiments soon as the discharge is made, the wire should of Messrs. Brook and Cuthbertson on the fusion become red-hot in its whole length, and then fall of metallic wires. Their conclusion was, that into fine globules. the action of electricity'on wires increases in 234. The gradually increasing effects prothe ratio of the square of the increased power : duced are very remarkable, when, on wires of the since two jars, charged to any degree, will meet same length and diameter, progressively strong four times the length of wire that one jar will charges are transmitted. If the charge be very melt; and this will be again quadrupled low, it is found that the color is changed to doubling the height of the charge.
yellow; it then becomes blue by a higher charge; 232. This law, adds Mr. Singer, I have found, then red-hot; then red-hot and inelted into balls; obtains in all accurate experiments with mo- and, if we increase the charge still further, it derate lengths of wire; and it is apparent in becomes red-hot, and drops into balls, then disMr. Cuthbertson's experiments, to some extent. perses in a shower of balls, and finally disapHis batteries usually contain fifteen jars, and pears with a bright flash, producing an apparent one of these is just sufficient to fuse half an smoke, which turns out when collected to be a inch of wire of oth of an inch diameter: but fine powder, consisting of the metal combined the whole fifteen jars combined, will fuse sixty with oxygen, and weighing more than the metal inches of the same wire. Mr. Singer made which was originally fused. some experiments with an iron wire of zboth of 235. The experiments and results already an inch diameter, on an extensive scale; but he enumerated do by no means form the boundary found that some of the charge was lost in per- of the power of the electric fluid; bodies which vading such a considerable length of wire, so, resist the most intense heat, produced in the much so, that the explosion of the battery, at common way, are by it converted into oxides in other times remarkably loud, was then scarcely a momeņt. Of this more will be said in a future audible. With a battery, however, of forty feet part of this article; in the meantime a few ex of coated surface, Mr. Singer says he frequently amples may be given, which properly belong to melted eighteen feet of the above-mentioned the present. The most laborious experimenters wire by a single explosion, and the phenomena on this part of electricity have been Cuthbertson were remarkably brilliant; a shower of intensely and Singer, of whose operations we shall here ignited globules being dispersed in every direc- avail ourselves, as being both numerous and tion. This law, however, Mr. Singer found to valuable. The apparatus used by Mr. Cuthvary with the thickness of the glass employed; bertson, and, in some of his experiments, by Mr. thick jars displaying the same intensity with a Singer also, may be thus described :comparatively small quantity of electricity; and 236. It consists of a glass cylinder ab, fig. 7, consequently having, as he expresses it
, less about eight inches high, and two inches and á. wire-melting power. Of this he produces a half diameter, mounted air-tight with two brass proof, furnished by his large Leyden jar, to caps. On the lower cap a is screwed a stopwhich we have already alluded; this jar, from cock, and above the cap is fixed a small roller, the extent of its coated surface, ought to have on which a quantity of wire, attached to a packmelted three feet of wire, with a charge of thirty thread at intervals of four inches, is coiled. A grains; but from its extreme thickness, which brass tube c, about three inches long, is screwed limited its electrical virtue, it would only melt into the centre of the upper cap b, and, by means • eighteen inches. Mr. Singer remarks, that this of a long needle, the end of the packthread and is correspondent with the conclusion of M. Ca- wire is thrust through it, and hog's lard is placed vendish, that the quantities of electricity re- in the tube, so that the wire and packthread quired to charge different coated jars of the same shall always move through it air-tight. In this extent, will be in the inverse proportion of their way the wire is extended in the centre of the thickness.
cylinder, and, when one length is exploded, 233. The fusion of wire may therefore be em- another may be drawn forward by means of the ploged as a measure of the quantity of electricity packthread, without opening the cylinder. For accumulated on any charged surface; for the ascertaining the quantity of air absorbed during preceding experiments show that any given the process, a gauge, represented by A, about ten quantity of electricity will fuse the same length inches long, made of a glass tube, is screwed of wire, whether that surface he disposed on two into the lower end of the stop-cock, and immerjars or one ; hence it may be inferred that the sed in a vessel of quicksilver, the rise of which, actual intensity of a charge does not materially when the stop-cock is opened, will be a measure affect its power in melting wire. This test is of the air absorbed. The air left in the receiver, therefore practically useful for the various elec- after a number of explosions, is always found to trometers measure only the intensity, and are as have been deprived of a portion of its oxygen; much affected by one jar as hy a battery of and, if hydrogen or nitrogen gas be substituted 100. When the fusion of wire is employed in place of atmospheric air, the metal will not as a test of electrical power, care should be taken suffer any oxidation, but will be fused, and that the length of the circuit be always the same, minutely divided. and that the degrees of ignition be uniform; for 237. To accomplish the complete oxidation a wire may be melted with but slight variations of metallic substances, a higher power is required of appearance when very different portions of than that which is merely adequate to fuse them, electricity are passed through it. The lowest The following is a statement of the comparative degree of perfect ignition ought therefore to be strength of the charges which Mr. Cuthbertson Vol. VIII.