b. One metallic arc is formed entirely of one metal, the other arc half of one metal, and half of the other. The arc o p (App. 2) consisting of platinum, the arc gi half of copper, half of platinum,-also one of the cups containing oil of vitriol, the other, nitric acid,―the deflection amounts to only 5°, when the copper is placed in the nitric acid; but to 40° when it is immersed in the oil of vitriolalthough the solution is much more rapid in the first case than in the second:-and copper with platinum immersed in nitric acid alone, produces a deflection of 90°; and in oil of vitriol alone, a deflection of 40°. In consequence of the small conductibility [decomposibility] of the oil of vitriol, the electricity developed by the copper and the nitric acid becomes neutralized directly on the metal. (De la Rive.) The arc op (App. 2) and g consisting of copper, i of zinc,—or, on the contrary, op and g of zinc, and i of copper,-and the cup a containing spring water, b acidulated water, or the contrary, the current is of the same strength in all four cases: it diminishes however more quickly when the zinc is immersed in the acidulated water, than when it is placed in the spring water. (Poggendorff.) c. Two Liquids and three Metals. The vessel a (4pp. 2) containing nitric acid, 6 water, and the arc op consisting of platinum, g of silver, i of copper, iron, lead, or zinc,-these last metals are positive, although they are much less attacked than the silver in the nitric acid. (Marianini.) Addendum. Pohl's Battery. One zinc and seven copper plates are separated from one another by seven layers of a moist conductor which does not surround them, but merely touches their surfaces. (App. 22; Z = zinc, C = copper, m = moist conductor.) The zinc at one end is connected by a metallic are with the copper, No. 7, at the opposite end; similarly, Ci with C, C with C5, and C3 with C. An electric current sensible to an interposed galvanometer goes through all the arcs, through the first and third in one direction, through the second and fourth in the opposite direction. The current in the first arc is the strongest, that of the second weaker, and that of the fourth weakest of all. (Pohl.) [The zinc in connection with C1, C, and C furnishes an example of the case of two metals with one liquid in two vessels, described on page 403. which goes from C' through the first arc to the zinc, and from C1 through This produces a current the second arc to C. So far the result is easily explained; but the origin of the current in the third and fourth arcs is not yet ascertained.] Compare Henrici. (Pogg. 53, 284.) Pohl's Contracted Pile. (Pogg. 50, 497.) INSTRUMENTS FOR THE PRODUCTION OF ELECTRIC CURRENTS BY MEANS OF CHEMICAL ACTION. I. Instruments consisting of a Simple Galvanic Circuit. Wollaston's Thimble Apparatus (Gilb. 54, 1),-the smallest simple galvanic circuit capable of igniting a metallic wire, is thus constructed. A copper thimble converted by removal of the bottom into a cylinder opened at both ends, is beaten flat-so that the opposite sides are brought within two lines of one another. In this space, a zinc plate not quite of an inch wide is fastened with sealing wax in such a manner as no where to come in contact with the thimble. To the upper end of the thimble is soldered a loop of silver wire. A platinum wire 1 inch long and of an inch thick is soldered to the upper part of this loop, and thence, carried in a slanting direction towards the zinc. Another similar wire fastened to the zinc plate proceeds in a direction opposite to the former, the two wires being fastened into glass bulbs, and running parallel to one another for a certain distance with a very small interval between them. Lastly these two wires are connected together in the middle by a very fine wire of platinum. To obtain this fine wire, a platinum wire of an inch thick is surrounded in a mould with a bar of silver of an inch thick. The compound wire thus formed is drawn out to the thickness of of an inch; a piece of it, an inch in length, is bent round, and the bent part immersed in nitric acid-which, by dissolving the silver, exposes a platinum wire of such extreme fineness that it can scarcely be seen by the naked eye. If now the ends of this wire still retaining the silver be drawn tightly over the two thick platinum wires, soldered to them with zinc and sal-ammoniac, and then the projecting parts cut off, the two thick platinum wires will be connected by means of a wire of extreme tenuity. On immersing this apparatus nearly up to its upper rim in a mixture of one measure of oil of vitriol and 50 of water, the fine wire-whose length must not exceed fromto of an inch-becomes incandescent and remains so for some seconds. [The negative electricity set free from the zinc as it dissolves combines in the very thin wire-through which it passes with difficulty -with positive electricity evolved from the thimble.] Hare's Deflagrator and Calorimotor. Large continuous surfaces of zinc on the one hand and copper on the other, placed near to one another but not in contact, are immersed in an acid liquid. If the copper and zinc be then connected by a thick metallic wire, positive electricity goes from the copper to the zinc, and negative electricity from the zinc to the copper, in very large quantity-so that connecting wires, even of some thickness are heated and fused, and a piece of charcoal placed between the ends is brought into a state of vivid incandescence. But the tension of the current is as low as when a small pair of plates is used. Hence when the connection between the copper and zinc is formed by means of imperfect conductors, such as liquids, the current is nearly stopped. Of the Deflagrator there are two forms: 1. A zinc plate, 6 inches broad and 9 inches long, and a copper plate, 6 inches broad and 14 inches long, are rolled up together into a cylinder 2 inches in diameter, in such a manner that they never come into actual contact, but remain at the distance of a quarter of an inch from one another, the last coil of the zinc being completely surrounded by the copper. All the copper plates of eighty such rolls are united by soldering with a single metallic rod, and thus connected with each other; a similar connection is made between all the zinc plates. When these rolls, suspended by a lever, are simultaneously immersed in eighty cylindrical glasses filled with dilute acid, and the two metallic rods connected by a platinum wire inch thick, the wire is instantly melted. Copper and mercury are burnt. A leaden tube being soldered to the extremity of the wire proceeding from the copper, and a pointed piece of charcoal fixed into the tube-then, on bringing this piece of charcoal near another piece similarly fitted to the zinc side, or near a platinum wire inch thick, connected with the zinc, a most dazzling light is produced (p. 317). 2. Two hundred and fifty zinc plates, each 3 inches wide and 7 inches long, are placed in 250 flat copper cases, open at top and bottom. Every 50 of these pairs are hung on a separate bar of wood. Each copper case is separated from the next by a covering of paste-board, coated with shellac varnish. In this manner, 50 copper cases are united into one dense mass. Under each of the 5 immovable bars is placed a trough, filled with dilute acid. All 5 troughs are placed on a common support, which can be let up and down-so that, on raising the troughs, the liquid contained in them fills the space between the zinc and copper. The effects produced by this apparatus are similar to those of the arrangement last described, or even stronger. In the Calorimotor, 20 copper and 20 zinc plates, each having a surface of 19 square inches, are fastened alternately and perpendicularly in a frame: all the copper plates are soldered to one common bar, and all the zinc plates to another. The whole is immersed in a trough filled with acid, and the copper connected with the zinc by a conductor. This apparatus produces similar but less powerful effects. With from 60 to 120 copper and as many zinc plates, platinum wire may be fused, &c. II. Instruments formed by the union of several Simple Galvanic Circuits. Voltaic Piles in the more extended Sense,—Galvanic Batteries. 1. The Simple Circuits consisting of two Metals and one or two Liquids. When two metals m, t, are connected with a fluid with which they form a simple galvanic circuit, in the following order: mft, mft, mft, &c., the following effects are produced. 1. In the outermost m on the left, and the outermost t on the right, examination with the electrometer (not the galvanometer) shows the presence of a quantity of free positive and free negative electricity, which increases with the number of simple circuits united:-indeed, the free electricity appears to increase in direct proportion to the number of simple circuits. 2. When one of the external pieces of metal is connected with the ground, and its free electricity thereby removed, the quantity of the opposite free electricity in the other external piece of metal is doubled. 3. When the two outside pieces of metal are connected by means of a good conductor-e. g. a wire-and the open circuit thereby converted into a closed circuit, the deflection of a magnetic needle in the neighbourhood of the wire is very little, if at all, greater than that which would be produced by a simple circuit consisting of the same elements,-provided that, in the latter case, the connecting wire is thick enough to afford free passage to electricity of small tension. 4. But the tension of the current increases with the number of simple circuits connected together; and hence, the current generated by a compound circuit can pass, with little or no diminution of strength, through long wires and imperfect conductors, by which the current of a simple circuit would be greatly enfeebled, or even completely arrested. 5. If, while the circuit is closed, the contiguous pieces of metal t, m, be separated, and then connected by a wire, an electric current will pass through every such wire, of the same quantity and tension as that which passes through the metallic arc connecting the two outermost pieces of metal. [Circuit open: If two pairs of metallic plates-e. g. of zinc and copper -are placed in two cups or cells a, b (App. 23), filled with the same liquid, acidulated water for instance, C being connected with Z2 by a wire gi, but Z1 not connected with C2 by the wire o p,--the negative electricity set free by the oxidation of Z2 may indeed pass over to C', and thence to the hydrogen set free by Z1:-but since the negative electricity set free in Z1 has no other way of escaping than by passing to the hydrogen of the cell a, and the hydrogen liberated in the cell b can only receive its negative electricity from Z3,-scarcely anything but purely chemical action takes place, and the hydrogen is evolved on the two zinc plates. But just as in the unclosed simple circuit (p. 342, c), so likewise in this case, a feeble electro-chemical action takes place: for, in consequence of the difficulty which the negative electricity finds in passing from the zinc to the hydrogen, a small quantity of negative electricitywhich may be called one negative portion-remains in Z1 and Z3. The small quantity of hydrogen which does not receive from the zinc the quantity of negative electricity belonging to it, either takes it from the caloric of the liquid and liberates positive electricity, which passes over to C1 and C,-or it is conveyed by transposition from Z to C, and from Z to C2, taking up negative electricity in both these plates, and liberating positive electricity (one positive portion (a) in each plate). The positive portion in C1 immediately unites with the negative portion in Z3 to form caloric (8); and since to the negative portion in Z, there longer opposed any positive portion in C, nor any negative portion in Z2 to the positive portion in C, and consequently the electrical difference is reduced one-half,-it follows that 2 negative portions can accumulate in Z1 and 2 positive portions in C2, till the tendency of the two electricities to combine prevents their further accumulation. Upon this, a second positive position passes into C and a second negative portion to Z (y); but these portions again neutralize one another (). Whereas, therefore, in the simple galvanic circuit, the zine contains one negative portion and the copper one positive portion of free electricity,-in the twopair circuit, on the other hand, Z1 contains 2 negative portions and C2 2 positive portions, while C1 and Z are neutral. This accumulation of a double quantity of negative electricity in Z and of positive electricity in C2, produces a twofold electrical tension. When three simple circuits are united (App. 24), one positive portion from C' is neutralized by one negative portion from Z2, and similarly, one positive portion from C by one negative portion from Z3 (a, B): and since these 4 plates are thereby rendered neutral, a second negative portion can accumulate in Z1 and a second positive portion in C3-whereupon the portions developed in the 4 middle plates again neutralize one another, (, ). But thirdly, 2 negative portions accumulate in Z3, half of which is communicated to C', and 2 positive portions in C, half of which is communicated to Z3 (, ). Since now Z', which already contains 2 negative portions, is opposed to C', with one negative portion, a third negative portion can accumulate in Z1, until the maximum is attained; -and in the same manner, 3 positive portions accumulate in C, which is opposed to Z3, containing one positive portion (). Lastly, the portions in C1 and Z3, and those in C and Z3, distribute themselves uniformly (9). Ꮓ 222233 According to this, the portions of electricity are distributed as follows in an unclosed circuit:-Simple Circuit: Z, C+. Two-pair Circuit: Z1 2 —, C1 0, Z2 0, C2 2+. Three-pair Cireuit: Z' 3-, C1 —, Z2 —, C2 +, Z3 +, C3 3+. Four-pair Circuit: Z1 4-, C1 2,2 Z2 2 - C2 0, Z2 3 Z3 0, C3 2+, Z' 2+, C' 4 +. Five-pair Circuit: Z5, Ci 3-, C2 —, Z3 —, C3 +, Z1 +, C1 3 +, Z3 3 +, C3 5 +, and so on. Hence the quantities of electricity accumulated in the terminal plates,— and, therefore, also the electrical tensions of the poles,-increase proportion to the number of plates. When one of the terminal plates is connected with the ground, e. g. C2 of the double circuit (App. 23), and the two portions of positive electricity thereby conducted away, a fresh accumulation of elrctricity takes place in the opposite terminal plate to the same amount as before, making in all 4 negative portions. For since C is neutral, 2 negative portions can accumulate in Ż3, till the maximum of tension is attained, and similarly in C', which is connected with it; so that Z1 opposite to C1 can now retain 4 negative portions. In the same manner, 4 positive portions accumulate in C when the electricity of Z1 is conducted away. Generally; whatever may be the number of pairs in the battery, the electrical tension of either pole is doubled when the electricity accumulated in the other pole is conducted away.] [Circuit closed: As soon as Z1 is connected with C (App. 23) by a metallic arc o p, electro-chemical action is enabled to proceed on an extended scale. The negative electricity developed by the oxidation of Z1 goes through op to C, and thence to the hydrogen liberated by Z3 from the water in cell b. The negative electricity evolved at the same time from Z3 passes through C to the hydrogen, which is transferred from Z1 to C'. Hereupon, negative electricity goes from o to p and from i to g,— what comes to the same thing, positive electricity goes from p to o and from g to i. or, The quantities of electricity flowing through op and gi are equal: the galvanometer shows the same deflection, whether it is interposed between op orgi. This is in accordance with the fact, that the quantity of hydrogen gas evolved on C' is the same as that on C. Suppose, for example, that the electro-chemical action were stronger on Z1 than on Z3: the quantity of negative electricity transmitted from Z1 to C would then be more than sufficient to saturate the hydrogen gas there evolved, while 7 would give to C a quantity of negative electricity less than that rered by the hydrogen evolved on C1. Hence the electro-chemical ons in the two cells control one another in such a manner, that equal |