ANALOGY BETWEEN THE PHENOMENA OF GAL

VANISM AND THOSE OF FERMENTATION. 617. M. Schweigger has observed this analogy in the following points :

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618. (1.) Galvanic piles, like fermentable mixtures, exhibit their effects only by the reciprocal action of three different bodies.

619. (2.) The products of galvanic action are two, an oxidated body, and a hydrogenated body. The same happens with the products of fermentation, which are alcohol and carbonic acid.

620. (3.) The presence of electro-negative bodies favors the decomposition of water, whilst, according to Dobino, a similar effect goes on in fermentation.

EXPERIMENTS ON THE IGNITION OF WIRE. 621. The following experiments on the ignition of wires are very interesting. Being connected with the phenomena of caloric developed in the action of the galvanic battery, they may be acceptable as a contribution towards that mass of facts which will at some future period assume a more scientific form.

622. In these experiments, Mr. Murray used four porcelain troughs, each containing ten cells, and each cell supplied with one and a half fluid ounce of the strongest nitrous acid, being filled up with water to the depth of two-thirds, and properly mixed with a glass rod. Nitrous acid, in this proportion, he has ever found best calculated for the development of galvanic action. Fifteen to eighteen inches of fine platinum wire may be readily ignited. He of course used the triad (four inches square), for which we are indebted to the sagacity of that ingenious and profound philosopher, Dr Wollaston.

623. When sulphuric acid is employed, as is done most injudiciously by some, in mixture with the nitrous acid, the vapor is perfectly intolerable, and much of the action is no doubt lost and expended in vapor, and in the great temperature developed at the same time.

624. In connexion with the subsequent detail, it may be proper to mention, that a riband of a platinum foil, was suspended from one of the conductors, and brought in contact with the mercurial surface (that metal being contained in a shallow glass-basin), while the other one is plunged into the mercury, deflagrates with great brilliancy, and oscillates like a pendulum.

625. We may now state generally, that steel and platinum wires may be intensely ignited, in alcohol, ether, and its vapor, oil of olives, naphtha, and sulphuret of carbon. Mr. Murray has not succeeded in igniting these in water, and

concludes that it is owing to the superior conducting property of that fluid. The degree of ignition, all circumstances being the same, will correspond with the .elations in which the medium containing the wire stands to conduction. 626. Platinum and steel wires may be ignited in carbonic acid gas, hydrogene, cyanogene, and olefiant gas.

627. Gold wire was wrapped round platinum in all its extent; and this double wire placed as the uniting wire between the conducting rods It was ignited throughout, and the fusion of the gold wire supervened, the gold being collected into little spheres of a prolate form, at equal distances, and appearing like a row of beads.

628. Steel wire was, in like manner, entwined with gold wire. It also was ignited in its whole extent; the gold wire was fused, and exhibited the bead-like form.

629. Platinum was woven with copper wire. The platinum wire was ignited throughout; the copper wire not undergoing fusion nor even ignition.

630. It may here be remarked, that, in the ignition and combustion of steel wire, for instance, the fusion is primarily confined to the surface, and the fused scale or film may, perhaps, not penetrate more than one-third the diameter of the wire, while the remaining part may not have undergone the least physical change. The fused matter formed itself into spherules, with regular intervals. This appears to be a curious phenomenon; and it will also be observed that, when the calorific heat is short of ignition, the steel wire will be blued in patches.

631. Steel wire was doubled for one-half its extent; the single and denuded part was alone ignited.

632. Platinum wire was doubled for one-half its extent; and that part only which was single could be ignited.

633. Steel wire was partly enveloped in gold wire; only that portion of the steel wire which was void of the gold wire could be ignited; the part encased in the folds of the gold wire was partially blued, and was rendered magnetic.

634. Copper wire was twisted round platinum wire, for half the length of the latter. The uncovered platinum was alone ignited. Copper wire was twisted around steel wire in the manner of the preceding; the naked steel wire was ignited alone. Steel wire was twisted round platinum wire, for one-half its length; only that portion of the platinum wire excepted from the steel could be ignited.

635. Peculiar phenomena are connected with these exhibitions. When the second wire is carried through the whole extent of the uniting wire, ignition is superinduced throughout; but when only partial, the ignition is confined to the denuded portion.

636. Copper, platinum, and copper wires, were linked together, and made the communicating chain. The platinum placed between the copper wires was ignited alone.

637. Platinum, copper, and platinum wires, exhibited, on the tract of either platinum wire, ignition, while the intermediate copper wire remained dark and unignited.

638. In the case of steel, copper, and steel wires (so linked together), the steel wire on each side was ignited, while the copper wire remained

unaltered.

639. In the chain of platinum, steel, and platinum wires, the platinum wires were exclusively ignited, and the steel unignited.

640. In that of steel, platinum, and steel, the ntermediate link of platinum was ignited, and the steel wire on each end remained without ignition.

641. In a chain of gold, steel, and gold, the gold wires on each end were ignited and fused, and the intermediate steel was not ignited.

642. In one formed of steel, gold, and steel wires, the central one of gold was exclusively ignited.

643. Mr. Murray next tried spiral coils of platinum and steel, of various diameters, and found that they were ignited, though curvilinear, in the same manner as if the wires were not curved.

644. The preceding experiments seem to prove, that the caloric developed in galvanic action, has no relation with the medium in which the ignition takes place; and that it is evolved in some inverse ratio of the conducting properties of the uniting wire.

645. The phenomena of ignition in links of rarious metals united into a chain, seem connected with the passage of a material agent through them, displaying its powers in greater or less ignition, according as the passage is interrupted, or its fire more or less retarded, and, of course, as the amount of the resistance. The agent or agents, therefore, developed in transitu from pole to pole, will swell into ignition, if the conducting power of the medium traversed is low, or even burst its metalline confine, and expend its impetus in all the brilliancy of an intense combustion. The gold, platinum, and copper wires, were th of an inch in diameter; and the steel the finest harpsichord wire. DESCRIPTION AND USE OF A VERY SENSIBLE ELECTROMETER, FOR INDICATING THE KIND

OF ELECTRICITY WHICH IS APPLIED TO IT. 646. Some years back, M. Behrens published the Description of an Electrometer, which indicates the kind of electricity that is presented to it; but it appears to have been forgotten, with the dry electrical columns, which formed an essent al part of the apparatus. The electrical perpetual motion of Zamboni is similar to this electrometer, and M. Butzengeiger was employed to execute one of them, which we may proceed to describe.

647. A cylindrical vessel of glass about two inches and a half in diameter, and three and a haif high, has fitted to it a brass cap, from which two small dry electrical columns descend into the vessel, and are attached to the cap by screws, so that the one has its positive and the other its negative pole, making a slight projection above the cap. Each column is composed of 400 dises of gold and silver paper, glued together, and three lines in diameter, so as to fill two tubes of varnished glass. Each of these tubes terminated below by a ring of brass, projecting a ittle, and rounded, which is in electrical com

munication with the discs. When the brass cap is in its place, the columns descend vertically, and the lower ring is one-fourth of an inch distant from the bottom of the glass. The axes of the columns are one inch and seven lines distant, but may be brought nearer one another. From the centre of the cap rises a tube of glass, varnished within and without, and within the tube is a brass wire kept in the axis by a cork, but touching the tube no where else. At the lower end of the brass wire is suspended a piece of gold leaf, two inches and a half long and three lines wide, exactly in the middle of the interval between the two columns, and parallel to their axis, if they are accurately vertical. At the upper end of the brass wire is a small brass ball, upon which may be screwed one of the discs of a condenser, as in the electrometer of Volta. By this arrangement, the electrical columns which Behrens had placed without the glass, which defends the gold leaf from the agitations of the air, are placed within the glass, so that their position is not only better preserved, but they are defended so completely from moisture, dust, &c., that they retain the same eler trical intensity.

648. This electrometer is used in the following manner :-The cap of metal is put in commu nication with the ground by means of a metallic wire, and by touching the brass ball, any accidental electricity is discharged, which may be long to this part of the apparatus. If the skin is dry, the touch of the finger is not suffi cient. As the gold leaf is suspended between the columns, at the level of the rings of metal which terminate them, the one positively and the other negatively, the gold leaf is attracted equally on both sides, and remains quietly in the middle in its ordinary state; but if, by means of the metallic wire, we communicate to it the weakest degree of electricity, the lower extremity of the gold leaf is attracted by the ring which possesses an electricity opposite to that which is communicated. Having come in contact with this ring, it is successively repelled and attracted by the opposite ring. This oscillatory motion continues till the gold leaf attaches itself to one of the columns, from which it may be easily detached by touching the brass wire, so as to dissipate its electricity, and by shaking the instru ment. In order to determine the nature of the electricity, the upper poles of the two columns which project above the brass cap have the signs and upon them, and the electricity required is that which is indicated by the sign of the column towards which the gold leaf first moves, or which it first touches, when the electricity is stronger.

649. By this electrometer, strong and weak degrees of electricity may be equally well examined. In the first case, the electrified body is made to approach slowly and at a distance the ball of the electrometer, till the gold leaf is put in motion towards one of the columns. If, for example, we bring an excited stick of sealing-wax to the distance of about three feet from the ball, we shall observe a motion of the gold leaf towards the column marked we bring it to a less distance, it will strike the column, from which it may be easily detached,

It

by bringing the wax still nearer. In the second case, the electrified body must be moved much nearer the ball, and brought into contact with it, if necessary, till the gold leaf is put in action. This degree of electricity is so weak, that it would be absolutely insensible in the ordinary electrometer of Bennet.

650. When the electricity is still feebler, we may advantageously employ a condenser adapted to the instrument. The circular plate, on the margin of which is screwed the ball of the electrometer, replaces the cover of the condenser, and a plate of disc furnished with a glass handle, and which is placed above the first, represents the base. These plates are covered with a thin coating of amber varnish on the faces which are brought into contact. If we wish to try a very weak electricity, we first touch, in order to deprive it of its electricity, the inferior plate, or the wire which carries the ball; we then place above it the other plate, and afterwards touch the lower plate or its wire, with the body whose electricity we wish to examine, touching at the same time, the upper plate, in order to deprive it of its electricity. The upper disc is then removed by its glass handle, and we observe towards which of the two small columns the gold leaf is carried, and the sign marked upon this column will indicate the kind of electricity. If, for example, we put in contact with the lower surface of the lower plate of the condenser a small disc of zinc, about three-fourths of an inch in diameter, and press it against this plate, without touching the plate with the finger, and if we touch at the same time the upper disc of the condenser, to deprive it of its electricity, and if we afterwards remove the disc of zinc on one side, and on the other side the upper plate, we shall observe the gold leaf approach the column marked minus. A similar effect will be observed, if we put in contact with the disc of the apparatus the metallic side of a piece of silvered paper.

651. It will often be more convenient to put the body we wish to examine in contact with the upper and moveable plate, and touching the inferior plate, to deprive it of its electricity, proceding in other respects as we have already described. The electricity, however, which the instrument now indicates, will be opposite to that which is communicated to the upper plate, because, by this method, the plate united to the instrument forms the base of the condenser.

652. If the body which we examine cannot be conveniently put in immediate contact with the lower plate of the condenser, a communication with it may be formed, by means of a metallic wire, with an insulating handle, the rest of the operation being the same as before. ELECTRO-MAGNETIC EFFECTS

OF ALKALIES, ACIDS, AND SALTS, BY M. YELIN. 653. The magnetic needle used by M. Yelin was nearly 1.5 inch long, and 008 of an inch in diameter. It weighed little more than half a grain, and was delicately suspended by a spider's web, from a rod passing through the top of a glass cylinder, so that it could be raised or lowered at pleasure. The bottom of the instrument

is a piece of card-board, on which circles are marked and divided, indicating the number of degrees through which the needle may have moved.

654. The conductor, whose state was to be indicated by this needle, was sometimes a band of tin 0-4 of an inch broad, and 24 inches long; sometimes a brass-wire helix, which, being brought up close beneath the needle, formed a kind of condenser, and rendered the action more sensible.

655. (1.) The tin band was placed under the needle, both being parallel to the magnetic meridian; a small glass was filled with muriatic acid; the end of the band, towards the austral pole of the needle, was plunged into the acid, and, in a few moments after, the other extremity was immersed; immediately the austral pole went to the east. The experiment being repeated, except that the end of the band, corresponding to the boreal of the needle, was first immersed; the austral pole went to the west. When, in place of muriatic acid, a solution of ammonia, mineral alkali (soda), or sal-ammonia, was used, the results were exactly the same; but if a solution of vegetable alkali (potassa) was used, the deviations were all in the opposite directions. Pure water produced no effect, but of acid made it active. All solutions of salts, or acid, thus applied, produced an effect upon the needle.

It appears in these cases that, according as the first contact is made to the right or left, an arrangement of molecules is established in the fluid, proper to form a species of pile of which the two poles are very distinct, and that the whole of this little pile is reconstructed in the opposite direction, when the contact is made in the opposite way.

656. Place the needle over the condenser, the wires of the latter and the needle being parallel to the magnetic meridian; hold a cylinder of zinc in perfect contact with each end of the wire of the condenser, the arrangement will then be zinc, brass, zinc; plunge the cylinder corresponding with the austral pole of the needle into muriatic acid, and then plunge the other into the same acid, the austral pole of the needle will go towards the east. Repeat the experiment with nitric acid and fresh cylinders of zinc; now the austral pole of the needle will go towards the west. These and other results are the same, whether the conductors are put in contact with the metals before or after their immersion in the fluid.

657. The needle condenser and metal bars (zinc), being as before, let the glass be filled with a solution of potassa, then immerse the end of the bar corresponding to the austral pole of the needle, and afterwards the other bar; the austral pole will deviate to the east. Take the bars out of the solution, but without changing their posi tion in the hands, and, as soon as the needle is at rest, introduce them again, beginning with the bar corresponding to the boreal pole of the needle; the needle (the austral pole) will now deviate to the west. Take the bars out of the fluid, and, without changing them from hand to hand, turn them so that the ends which were before immersed in the liquid, shall now be in contact

also free to take any direction; lastly, the needle is insulated from the action of terrestrial magnetism, by opposing to it the north end of a small bar magnet in the line of the dip. By this means the needle retains its magnetic power, but is under no magnetic influence.

669. The extremities of the curves being now connected with the poles of the battery, the globe immediately becomes strongly active upon the needle, causing it to assume the same dip, and the same direction, with respect to the artificial globe, as the actual needle does in the corresponding part of the earth itself, at least to a very considerable extent. Thus, if we bring the Island of Ascension to the zenith, the needle is found perfeetly horizontal, with a slight westerly variation. If we bring London to the zenith, we find the dip about 70°, and 24° or 25° of westerly variation; if the globe is again shifted in position, so as to bring Cape Horn in the zenith, the dip is about 60° the contrary way, that is, with the south end below; and the variation about 30° easterly, and so on with various other places.

670. The purpose of this experiment is to show, that what we have hitherto considered as the magnetism of the earth, may be only modified electricity, and to illustrate, experimentally, the theory advanced by M. Ampère, who attributes all magnetic phenomena to electrical results.

ROUSSEAU'S APPARATUS.

671. M. Rousseau, who has been occupied several years in the construction of dry Voltaic piles, has conceived the idea of employing those instruments to appreciate the different degrees of conducting power of the substances arranged in the class of bad conductors of electricity. For this purpose he has contrived the apparatus we are about to describe. The dry pile, which forms the principal part of it, is made of discs of zinc and tin-foil, separated by pieces of parchment, soaked in a mixture of equal parts of oil of poppies and essence of turpentine; the whole is covered laterally with resin, to prevent the contact of the air. The base of the pile communicates with the ground. Its upper extremity may be connected by a metallic wire with an insulated vertical pivot, carrying a weakly magnetic needle, balanced horizontally. On a level with the needle, and distant from the pivot, about half the length of the latter, is a metallic ball, also insulated, but communicating with the pile. It is evident that, by this arrangement, the electricity accumulated at the upper pole of the pile is communicated to the needle and the ball; and consequently repulsion ensues, tending to separate the needle, which is moveable, from the ball which is stationary. If we place the pivot and the ball in the magnetic meridian, the needle touches it, and remains at rest as long as the apparatus is not connected with the pile; but the instant the communication is established between them, the needle is repelled; and, after some oscillations, takes its position of equilibrium, depending on its magnetic power and the energy of the pile. These two quantities remain constant for a considerable time, with the same apparatus,

as may be ascertained by determining the angle which the needle makes with the magnetic meridian, after it has assumed a fixed position, by means of a divided circle adapted to the cage which covers it. A simple conducting needle, suspended by a metallic wire of proper diameter and length, might be substituted for the magnetic one; but M. Rousseau's apparatus is much more convenient, and sufficiently sensible for the kind of effect which it is his object to measure.

672. To use it for ascertaining different degrees of conducting power, it is sufficient to place the substance submitted to experiment in the electrical current, taking care that the thickness which the electricity has to pass through be always equal. If the flow of the quantity of electricity necessary to produce the greatest deviation be not instantaneous, the time required by the needle to assume its fixed position may be taken as the measure of the degree of the conducting power of the substance employed.

673. To submit liquids to this kind of examination, M. Rousseau places them in small metallic cups, communicating by their foot with the needle and the ball: he then places in the liquid one of the extremities of the metallic wire, covered with gum lac, that the same surface of metal may always be in contact with the fluid, and measures the duration of the needle's motion from the moment when the communication is established with the pile by the other extremity of the wire.

674. By submitting the fixed vegetable oils employed in the arts and in domestic economy to this kind of proof, M. Rousseau has established a very singular fact, which may be useful in commerce; it is, that olive oil possesses a very inferior degree of conducting power to that of all other vegetable or animal oils, which nevertheless present, in all their physical properties, . the strongest analogies to that substance. For instance, every thing being equal in both cases, olive oil required forty minutes to produce a certain deviation, while poppy oil, or the oil of the beech-mast, required only twenty-seven seconds to produce the same deviation. One-hundreth part of any other oil added to oil of olives reduces the time to ten minutes. It would, therefore, be easy to discover, by means of this instrument, the smallest traces of any oil fraudulently mixed with oil of olives.

675. If the proportion of the foreign substance be considerable, the difference of time necessary to produce the maximum of effect would no longer be sufficiently great, and could not be measured with sufficient precision to indicate the proportion of the elements, but the apparatus might easily be modified so as to adapt it to this kind of determination.

676. The solid fats are worse conductors than the animal oils, arising, no doubt, from the large proportion of stearine contained in the former; for M. Rousseau is satisfied, by comparative trials with stearine and elaine, prepared by M. Chevreul, that the conducting power of the latter much exceeds that of the former. The fat of an animal becomes a worse conductor in proportion to the age of the individual which affords it.

677. By means of the same apparatus, we