inches, liberates 6 cubic inches of detonating gas per minute, when the connecting wires are made to dip into water acidulated with sulphuric acid,— brings a platinum of 7 inches long and of an inch thick to a state of bright ignition-and causes steel needles to burn with brilliancy. (Grove.)

A five-pair battery of this description having in each earthenware cell a platinum plate, 8 inches long and 2 inches wide, immersed in nitric acid of 1.35 sp. gr.,-and in each porcelain cell a zinc plate of double the size bent round at the bottom and immersed in hydrochloric acid-yields 15 cubic inches of detonating gas per minute, fuses platinum wire of the thickness of a knitting needle in a few seconds, causes charcoal to emit a light of intolerable brilliancy, and will produce a magnet capable of bearing 3 cwt. Its physiological effects however are but slight [on account of the feeble tension of five pairs]. The current is likewise of constant strength. (Schönbein, Pogg. 49, 511.)

Porcelain cylinders, closed at bottom and covered on the outside with a layer of platinum burnt in, may be placed in cylinders of porous earthenware filled with nitric acid, and these again in vessels containing cylindrically bent zinc plates with dilute sulphuric acid, or still better, sulphate of zinc. (Pfaff, Pogg. 53, 303.)

Instead of platinum, an iron rod may also be immersed in strong nitric acid contained in a tube of gypsum, and the tube placed in a vessel containing dilute sulphuric acid, in which is immersed a zinc plate bent into the form of a cylinder. After this battery has acted for some time, the acid becomes so much weakened that it dissolves the iron suddenly. (Hawkins, Phil. Mag. J. 16, 115.-Poggendorff's Arrangement, Pogg. 54, 425.)

When the following carbonaceous substances are used instead of platinum in Grove's battery, the quantity of detonating gas evolved in a given time is found to diminish as follows:-Platinum: 3.52;--graphite: 34;-gas-coke, such as is deposited in the form of a hard crust in the retorts in which illuminating gas is generated: 3.27;-well burnt charcoal: 3:17. The action of all these substances is therefore nearly the same as that of platinum. (Cooper, Phil. Mag. J. 16, 35.)-Schönbein (Pogg. 49, 589) found the same result with gas-coke.-Charcoal having a surface of 8 square inches liberates as much gas as platinum 7 square inches in surface. (Smee.)

Bunsen (Ann. Pharm. 38, 311; Pogg. 54, 417) forms cells of carbonaceous substance prepared in the manner already described (p. 392), fills these cells with a mixture of sand and nitric acid, which is renewed from time to time as it is used up,-and places them in dilute sulphuric acid, also containing the zinc plates. A battery of three such pairs with zinc plates 3 inches wide and 4 inches long, liberates from 38 to 45 cubic centimetres of detonating gas per minute,-while, for every atom of water decomposed, not much more than one atom of zinc is dissolved in each cell. Platinum wires of some thickness are made red-hot, and charcoal brought to a state of dazzling incandescence. (Vid. Poggendorff, Pogg. 54, 419.)

Wöhler & Weber (Ann. Pharm. 38, 307) form two cylinders, open above and below, out of a piece of polished iron plate: one of the cylinders is made wider than the other, and the two are connected by a bent piece of metal. The wider cylinder is placed in a glass vessel containing dilute sulphuric acid,--in this is immersed an earthenware cylinder filled with strong nitric acid,--and in this, the narrower cylinder of the following pair. The iron in the sulphuric acid acts like zinc, that in the nitric acid

like platinum. When the surface of the wider cylinder is only three square inches, two pairs of this arrangement are sufficient to raise thin platinum wire to a white heat. Tinned plate appears to be preferable for immersion in the nitric acid; it is perhaps most advantageous to have the whole made of cast iron. (Wöhler.)

Three pairs of iron cylinders having a total surface of 12 square inches, three iron cylinders in nitric acid of 144 sp. gr. and the three others in a mixture of 7 parts water and 3 parts oil of vitriol, yield of a cubic inch of detonating gas per minute.-Five pairs of tin-plate (instead of zinc) and iron-plate (instead of platinum) having a total surface of 83 square inches, yield 18 cubic inches of detonating gas per minute, whereas an apparatus of zinc and platinum of the same size yields 9 cubic inches. (Walchner, Ann. Pharm. 40, 121.)

Aqueous solution of sesquichloride of iron in Grove's apparatus produces an action less by one fourth than that of nitric acid. (Smee.)

Grove's battery is stronger than any other of equal surface: its disadvantages are, the great expense, the inconvenience caused by nitrous fumes and the use of corrosive nitric acid,—and the mixing of the liquids by endosmose.

2. Batteries with two Metals and one Liquid.

A. The negative metal having twice as much surface as the positive metal.

Faraday, adopting Hare's method, makes two rectangular bends in the middle of a copper plate kk (App. 31), so that the sides run parallel to one another; he then solders the upper end of one-half of the plate to a zinc plate z by means of a bent piece of metal b,--and connects several such pairs in such a manner, that the zinc plate of the first shall be inserted between the two copper plates of the second, and kept from touching the copper by the introduction of small pieces of cork, of an inch thick,—the zinc plate of the second between the two copper plates of the third, and so on. The copper plates of one pair are kept from contact with those of the next by the insertion of thick paper. But as the paper becomes saturated with nitric acid, and this acid dissolves copper, which is subsequently precipitated on the zinc, it is better to separate the copper plates by strips of glass. The plates thus arranged are placed in the division a of the double trough represented in App. 32. Forty pairs require a trough 15 inches long, and 100 pairs a trough 3 feet long. The double trough is moveable round the axis x. A quarter revolution brings the trough 6 below and the trough a on the side, so that the acid liquid runs from a into b. Hence it is only necessary to turn the apparatus a quarter round, in order to bring the acid in contact with the plates or to discharge it; thus, all unnecessary action of the acid on the zinc is avoided. The intervals between the copper and zinc iu this apparatus being much smaller than in the common trough battery, and the quantity of acid liquid employed being consequently much less, the liquid becomes more quickly saturated, and must be more frequently renewed. An apparatus of this description, containing forty pairs with a surface of three square inches, acts as strongly as an ordinary trough apparatus (with single copper surface) containing orty pairs, having a surface of four square inches. (Faraday.)

Sturgeon's Battery consists of eight cast-iron cylindrical vessels, 10 inches high and 3 inches in diameter: in each of them is placed an amalgamated zinc cylinder, connected with the next iron vessel by means of a

thick copper wire, to which it is soldered, and fixed into a wooden ring which prevents contact between the zinc and iron. The vessels contain a mixture of 8 parts water and 1 part oil of vitriol (a mixture which acts by itself on amalgamated zinc). The battery makes thick platinum wire red hot, yields from 4 to 5 cubic inches of detonating gas per minute, and, though not exactly constant, continues in action for a long time. (Mohr, Pogg. 51, 372.)-According to Sturgeon, the following batteries, each having ten pairs of plates, with a surface of 104 square iuches, yield the following quantities of hydrogen gas per minute by the decomposition of water: Sturgeon's, 25; Grove's, 24; Smee's, 15; Daniell's, 12 cubic inches.

Children's Battery consists of forty copper and twenty zinc plates, each 6 feet long and 2 feet 8 inches wide, each zinc plate being placed between two copper plates (Phil. Tr. 1809, p. 32. Schw. 1, 374; 9, 212; 16, 359; also Gilb. 36, 334; 52, 353.)

Wollaston's Cell Apparatus. Zinc (plates are immersed in long and deep, but narrow, copper cells, filled with an acid liquid. The first cell is connected by a semicircular strip of metal with the zinc plate which dips into the second cell, and so on. (Compare Hart, Ed. J. of Sc. 4, 19.)— The apparatus of the Florentine Museum consists of six zinc plates. each 85 inches square, immersed in six copper cells. (N. Tr. 6, 1, 219.)—If the cells are made of platinized silver or platinized plated copper (p. 419), and contain a mixture of 1 measure of oil of vitriol with 8 measures of water in which zinc plates are immersed, the battery acts very strongly, and will continue in action for forty-eight hours without requiring fresh acid. (Smee.)

De la Rue (Phil. Mag. J. 9, 484; 10, 244) fills the copper cells with solution of sulphate of copper, and places an amalgamated zinc plate in each (an unamalgamated zinc plate would become covered with copper). The action is stronger than with acids, and no gas is evolved.

Young's Battery (Phil. Mag. J. 10, 241; also Pogg. 40, 625), in which two connected zinc plates are interposed between two connected copper plates, in such a manner that one of the zinc plates is placed between the two copper plates, and one of the copper plates between the two zinc plates, does not possess any particular advantage.

B. The surface of the negative metal not greater than that of the positive

metal.

Simple Trough or Cell-Apparatus. Oblong troughs of earthenware are divided into cells by earthenware partitions. Each cell contains a pair of plates of the two metals not in contact with each other; the positive plate of the first cell is connected by a curved strip of metal with the negative plate of the second cell, &c., &c. All the cells contain the same liquid. The number of pairs used in this kind of battery is, for the most part, greater than in those previously described; hence the tension is greater; but the quantity, unless very large plates are used, is smaller.

The battery of the Royal Institution of London consists of 2000 pairs of plates, each plate having a surface of 32 square inches on one side. At the Ecole Polytechnique, in Paris, there is a trough battery of 600 pairs of plates, each plate having a surface of 11 square inches. (GayLussac & Thenard, Recherches, 1, 1.)

In the Cup-apparatus (Couronne des tasses) a number of copper wires bent knee-shape, and each having a ball of zinc fused on to one of its ex

tremities, are immersed in a series of glasses containing dilute acid, in such a manner, that the zinc end of each wire dips into one glass and the copper end into the next. The action is but slight, on account of the small surface of the metals.

If twenty-four bent iron wires be covered at one end with peroxide of lead (by precipitation in the voltaic circle), and their ends made to dip into twenty-four glasses containing 1 part of nitric acid in 100 parts of water, each glass containing the clean end of one wire and the coated end of another, a battery is obtained which gives slight shocks, but loses its power as the peroxide of lead dissolves. (Schönbein.)-An apparatus of twelve platinum and twelve passive iron wires, immersed in nitric acid of sp. gr. 1.35, produces a very feeble current, which scarcely decomposes iodide of potassium, and has no effect on sulphate of copper or acidulated water. (Schönbein.)

In the Voltaic Pile, properly so called, the pairs of plates are disposed in alternate horizontal layers, with pasteboard, woollen cloth, or felt, saturated with a saline solution of dilute acid, &c. It acts like the trough-battery, but evolves less electricity in a given time, because the contact of the liquid with the metals is less complete.

Instead of plates of copper, Straub (Schweiz. naturw. Anzeiger, Jahrg. 4, S. 7,) recommends layers of carbonaceous matter. To prepare these, 7 parts of beech-wood charcoal, in fine powder, are mixed with 44 parts of wheat flour, and a proper quantity of water, into a paste; the paste is then moulded by pressure into flat circular pieces; and these, after being dried in sand in the open air, are exposed for three or four days to a continually increasing heat, till they smell like burnt bread. They are then ground quite smooth upon sand-stone, ignited between charcoal powder, and ground again. Before using them, they are soaked in water; after use, they are steeped in dilute hydrochloric acid to free them from zinc, and then washed.

De Luc's or Zamboni's Pile. The so-called Dry Pile is usually formed of thin sheets of metal separated by paper,-e. g., of discs of so-called gold and silver paper, joined together by their paper surfaces-or of silver paper having its paper side smeared with honey, and then sprinkled with peroxide of manganese. Since the number of plates in these piles can easily be raised to several thousands, the poles exhibit sufficient tension to give sparks. But the quantity of the electric current, which can arise from nothing but the chemical action of the hygroscopic water in the paper on the tin of the so-called silver paper, is extremely small. Hence the poles, after being discharged, take a long time to recover their former tension; the pile produces no ignition of metallic wires, and does not readily exhibit chemical action. It was only by employing plates of greater size than those generally used, that Bohnenberger obtained a slight decomposition of water. The pile when perfectly dry gives no more electricity (Parrot, H. Davy), and the quantity which it yields is greater in proportion to the quantity of moisture which it contains. (Parrot.) If the pile be dried by surrounding it with chloride of calcium, and raising its temperature, it will afterwards exhibit no electricity at ordinary temperatures, but will become electrical when heated. At temperatures between 70° and 75°, the tension of the poles is even greater than in an undried pile at ordinary temperatures. But when the poles have been discharged, the accumulation of electricity in the dried pile is much slower than in one which has not been perfectly dried. (Jäger.)

In the undried pile also, the tension of the poles is increased by heat

ing to 24; the application of a stronger heat produces no perceptible increase of tension. In vacuo, the pile exhibits the same tension as in the air. If the positive pole be connected with the conductor of an electrical machine, the negative electricity of the opposite pole sinks to 0; but when the negative pole is connected with the conductor, the tension of the positive pole increases. (Donné.) After the lapse of some time, the tin of the silver paper becomes dull and tarnished (H. Davy), and the pile gradually loses the whole of its power. (Jäger.)

Comp. Zamboni (Gilb. 60, 151); Heinrich, Schübler, Schweigger (Schw. 15, 113, 126, 132); Jäger (Gilb. 62, 227); Donné (Ann. Chim. Phys. 42, 71,-abstr. Schw. 58, 81); Rosenchöld (Pogg. 43, 193, and 440.)

3. Batteries consisting of one Metal and one Liquid.

If square pieces with long tails be cut out of zinc or tin-foil, and placed in about thirty watch-glasses filled with water, and arranged near one another, so that a square may lie in one watch-glass and the strip attached to it in the next, and consequently each watch-glass, excepting the first and last may contain a square and a strip belonging to two different pieces of metal,-the arrangement thus produced will be Zamboni's Pile of two Elements. In such a case, according to Zamboni, the first watch-glass into which the first square dips, or the pole towards which all the squares are directed, is negative, and the last watch-glass into which the last strip dips, or the pole towards which all the strips are directed, positive. With copper-foil, the opposite arrangement of the poles takes place. [According to this, the piece of zinc or tin of greater surface must be negative towards that of smaller surface, and the contrary with copper.] But, according to Erman, the positive pole in the zinc-foil arrangement is that towards which the squares are directed, and the negative pole that towards which all the points are directed; the contrary with silver. According to Erman, also, the current continues for two days only at the utmost, and may then be reproduced for a shorter time by the addition of common salt to the water.

If pieces of so-called gold-paper (or silver-paper) be formed into a pile, the metallic pole of this pile is positive, the paper pole negative. (Erman.) [Is the surface of the metal which is turned towards the paper less smooth than the outer surface?]

If eighty zinc plates, 4 square inches in surface, polished on one side and rough on the other, be placed in a wooden trough at the distance of 1 or 2 millimetres from one another, so that they may be separated by thin strata of air, and one pole of this pile be connected with the electroscope, the other with the ground,--the electroscope receives a considerable charge. The two surfaces of the zinc, being of different degrees of smoothness, act like two metals, and the film of air supplies the place of a liquid. (Watkins, Pogg. 14, 386.) [This deserves verification.]

On filling a number of copper vessels, 1, 2, 3, 4, 5, 6, 7, 8, with dilute sulphuric acid, connecting 1 with 2, 3 with 4, 5 with 6, and 7 with 8, by means of brass wires,- -on the other hand, 2 with 3, 4 with 5, and 6 with 7, by means of bundles of thread saturated with salt-water,-and heating only the vessels 1, 3, 5, and 7,-a current is produced, sufficient, when fourteen vessels are used, to decompose water, if the electricity be conAs the heated vesducted through that liquid by means of brass wires.

sels cool, the current ceases. (Schweigger, N. Gehl. 9, 704.)