the decomposition under naphtha: the moist potassa being placed between two plates of platina in a proper vessel, which is to be filled with naphtha as soon as the contact with the battery is established; in this way the action of the air is prevented, but the naphtha decomposes, and hydrogen and charcoal are liberated, which renders the result less satisfactory than in the more simple form of the experiment. The most essential precautions are to preserve the alkali as dry as is consistent with a sufficient degree of conducting power, and to employ the battery in a moderate state of action, in which it does not produce a very intense heat, for that would destroy the metallic base at the moment of its production.

158. The amalgam of potassium, or sodium, with mercury, is easily procured; and may be obtained by a very moderate power. A glass tube, one-fourth of an inch diameter and three inches long, having a short platina wire sealed in one end, is to have mercury poured into it until the end of the platina wire is covered; the rest of the tube is to be filled with a concentrated solution of alkali, either pure or carbonated. The platina wire, surrounded by mercury, is then to be connected with the negative end of a Voltaic battery, and the circuit completed by bringing a platina wire from the positive end, in contact with the solution of alkali. Gas will be evolved from this wire, and the surface of the mercury will be greatly agitated; when the action grows weaker, the mercury may be poured into a glass of water, and the presence of the alkaline metal will be immediately indicated by the evolution of a cloud of minute bubbles of hydrogen gas, which may be collected by inverting over the mercury a small closed glass tube filled with water. This result has been frequently obtained with a battery of thirty pairs of plates of only two inches square.

159. The amalgam may be obtained more highly charged with the alkaline metal by employing a solid piece of alkali, with a small cavity on its surface, in which a globule of mercury is to be placed. The alkali is to be connected with the zinc surface of a battery, and the mercury with the copper surface; the mercury soon becomes more tenacious, and sometimes is converted into a soft solid mass, and in this state, if thrown into water, it produces a rapid decomposition.

160. The strong attraction of the metals of the alkalies for oxygen, renders them most active agents of chemical decomposition; by the strongest Voltaic power they can only be obtained in small quantity; and for the purpose of experiment they are now usually procured by another process first devised by the French chemists. A gun-barrel is bent nearly in the form of the letter S. An iron tube of the capacity of two cubic inches, having a small hole at the lower extremity and an iron stopper at the top, is ground into one end of the gunbarrel, and a tube of safety is fitted to the other. The iron tube is to be filled with pure dry potassa, and the bent part of the gun-barrel nearest to it, with clean iron turnings: this part of the barrel is to be luted and placed in a small blast furnace; the

iron tube projecting out on one side, and the vacant part of the gun-barrel, with its attached tube of safety, charged with clean oil, or naphtha on the other. A strong heat is then to be raised in the furnace, and, when the iron turnings have attained an intense white heat, a small furnace is to be applied to the tube containing the potassa, which, being readily fused, will flow through the small hole at the bottom of the tube upon the iron turnings. The oxygen of the potassa combines with the heated iron, and the potassium condenses in brilliant lamina in the vacant part of the gun-barrel, which must be kept cool by ice during the process. As potassa always contains water, that is also decomposed, and hydrogen escapes during the experiment, from the tube of safety; the cessation of this liberation of gas is the sign for removing the small furnace from the tube, and the heat being raised in the blast furnace for a few minutes, as high as possible, to expel the last portions of potassium from the iron, the whole apparatus is suffered to cool. The gun-barrel is then to be cut at the commencement of the part which has been kept cool, for there the greatest portion of potassium is usually found; it must be detached by a chisel in as large pieces as possible, and introduced quickly into naphtha, a portion of which fluid it is expedient to pour into the barrel as soon as it is first opened.

161. This process is attended with some difficulty, but it has been repeated successfully by many chemists in this country: a more detailed account of it may be consulted in the thirtysecond volume of the Philosophical Magazine, pp. 89, and 276.

162. The composition of the fixed alkalies was entirely unknown before these experiments, but the volatile alkali, or ammonia, had been shown to consist of hydrogen and nitrogen, in the proportion of three of hydrogen to one of nitrogen by volume. Now it is singular, that of three bodies, whose properties are so analogous, two should be metallic oxides, and a third a compound of two gases; but there are experiments that seem to prove that either one or both of these gases contain a metallic substance, and that consequently ammonia may be, like the other alkalies, a metallic oxide.

163. Messrs. Berzelius and Pontin of Stockholm, discovered that when mercury is placed in a Voltaic circuit with a solution of ammonia, the mercury being connected with the copperextremity of the battery, and the ammonia with the zinc, the mercury gradually expands to four or five times its original volume, and becomes a soft solid, nearly of the consistence of butter, having its metallic character quite unimpaired. It is very remarkable, that by this change it gains only about part of its weight; yet has its specific gravity so much diminished, that, from being thirteen or fourteen times heavier than water, it becomes only three times heavier. By a short exposure to the atmosphere, it regains its original size and fluidity, absorbing oxygen and reproducing ammonia. When thrown into water a similar effect is produced, the water being decomposed and hydrogen liberated.

164. These phenomena are very analogous to those observed with the fixed alkalies; some substance combines with the quicksilver and alters its properties materially, without imparing its metallic character; now, according to all existing analogies, this substance must be a metal, and this metal, in returning to the state of alkali, absorbs oxygen, as is seen by its action on water. Hence it appears that ammonia consists of oxygen and a peculiar metal which may be called ammonium; but its analysis by other means evinces only the two gases, hydrogen and nitrogen; the former of these being the lightest of all gravitating bodies, is most probably a simple or elementary substance; and, on such a view, it would seem that nitrogen, though a gaseous body, is a compound of oxygen and a

metal.

165. The amalgam of ammonium may be formed most readily by making a cavity in a moistened piece of muriate, or carbonate of ammonia, connected with the positive side of a Voltaic battery, and inserting in it a globule of mercury connected by a platina wire with the negative surface; in a few minutes a soft amalgam is formed; it must be transferred into water as quickly as possible when its action on that Buid is to be observed, as it changes by the shortest possible contact of the air.

166. Sir H. Davy has observed, that the strong attraction of potassium for oxygen, enables it to decompose ammonia even more rapidly than the Voltaic battery; and if an amalgam of potassium and mercury be placed in a cavity in moistened muriate of ammonia, it immediately increases in size, and becomes more consistent.

167. As some of the substances called earths resemble the alkalies in various properties, it was conjectured, that they also were metallic oxides; and this conjecture has been partly verified by the experiments of Messrs. Pontin and Berzelius, and Sir H. Davy. If a paste be formed with water, and either barytes, strontites, lime, or magnesia; and this paste be connected with the positive side of a Voltaic battery, and touched with an iron wire proceeding from the negative surface, the wire obtains the property of decomposing water.

168. If a globule of mercury be placed in a cavity in the earthy body, and touched with a wire proceeding from the copper end of the battery (the paste being connected with the zinc), an amalgam will be soon formed, which has the property of decomposing water, and forming with it a solution of the earth employed. If this amalgam be introduced into a little tube made of glass, and bent in the form of a retort, then filled with the vapor of naphtha and hermetically sealed; on the application of heat to the end of the tube containing the amalgam, the mercury will distil over and leave the pure metal of the earth behind. This process is rather difficult, and requires great care.

169. The amalgam from barytes, strontites, and lime, may be obtained with a battery of from 100 to 200 four-inch plates, in a moderate time; that from magnesia requires a longer continuance of the action of the battery, and the other earths do not readily yield to its powers. These metals are named from the earths of which they appear

to be the bases, as follows: namely, that from barytes, barium; strontites, strontium; lime, calcium; magnesia, magnesium; alumine, aluminum; silex, silicum, &c.

170. The decomposition of the alkalies and earths which had previously resisted every attempt at analysis, are a monument of the importance of the Voltaic apparatus as an instrument of chemical research; and a proof of the ability with which it has been employed, which will be regarded with admiration and applause as long as science shall continue to be cultivated.

171. The phenomena that have been described as the consequences of Voltaic decomposition obtain in every variety of experiment. Sulphuric acid introduced into the Voltaic circuit gives off oxygen gas, and sulphur is deposited. Phosphoric acid evolves oxygen gas, and phosphorus combines with the negative wire. Ammonia separates into hydrogen and nitrogen with a small proportion of oxygen. Oils, alcohol, and ether, when acted on by a powerful battery, deposit charcoal, and give off hydrogen, or carborated hydrogen. And professor Brande has shown, that when animal fluids containing albumen, are placed in the Voltaic circuit, the albumen is separated in combination with alkali at the negative wire, and in combination with acid at the positive wire; and that, with a powerful battery, it separates at the negative wire in the solid form; and with a less power, in the fluid form, so that it is probable animal secretion may depend on some such power.

Prior to an examination of the Voltaic apparatus there are some simple experiments that should be noticed.

172. If a wire of silver, and another of zinc, be immersed in a glass coutaining dilute muriatic acid, so as to remain at a little distance from each other, the zinc will give off hydrogen gas rapidly, but the silver will produce no effect. Bring the ends of the wires that are out of the acid in contact, by twisting them together; the quantity of hydrogen given off by the zinc will be diminished, and bubbles will be evolved from the silver.

173. If zinc, iron, or copper, are employed in the same way with gold, in dilute nitric acid, similar phenomena ensue, but the gas produced is nitrous gas.

174. If a wire of iron and another of silver are immersed in a solution of copper, the iron will soon become coated with copper, but the silver will remain unchanged. Bring the wires in contact, by twisting their upper extremities together, and the silver will be soon covered with a coat of copper.

175. Similar experiments may be made with a zinc and a silver wire, in solutions of lead or tin.

176. Dr. Wollaston, to whom we are indebted for the last two experiments, thus accounts for the result: We know that when water is placed in the circuit of conductors of electricity, between the two extremities of a pile, if the power is sufficient to oxidate one of the wires of communication, the wire connected with the opposite extremity affords hydrogen gas.

177. Since the extrication of hydrogen in this instance is seen to depend on electricity, it is probable, that in other instances, electricity may be also requisite for its conversion into gas. It would appear, therefore, that in the solution of a metal, electricity is evolved during the action of the acid upon it; and that the formation of hydrogen gas, even in that case, depends on a transition of electricity between the fluid and the metal.

178. We see moreover, in a former experiment, that the zinc, without contact of any other metal, has the power of decomposing water; and we can have no reason to suppose that the contact of the silver produces any new power, but that it serves merely as a conductor of electricity, and thereby occasions the formation of hydrogen gas.

179. In the last experiment, also, the iron by itself has the power of precipitating copper, by means of electricity evolved during its solution; and here likewise the silver, by conducting that electricity, acquires the power of precipitating the copper in its metallic state.'

180. The experiments of this ingenious philosopher, by which the attraction of alkali, and the precipitation of copper on the surface of silver, were produced by the influence of negative electricity, excited by the ordinary machine, were considered by him as favoring the preceding explanation, and proving that oxidation must be the primary cause of electric phenomena. To Mr. Singer, who furnishes the quotation, they did not appear to favor any such supposition, but rather the contrary; for in the experiment with two different wires, touching each other, both produced the same chemical effects, yet, observes Mr. S., if they are electrical at all, the one is positive and the other negative, as all experiments on the association of different metals prove; and if two wires that have no chemical action on the fluid in which they are immersed, be rendered respectively positive and negative, they are well known to produce different chemical effects.'

181. But it is said the chemical effect produced by the silver wire, arises from electricity communicated to it by the zinc; and that we have no reason to suppose that any new power is produced by the contact of the metals. Now, if this were the case, the mere conducting communication of the metals would be the only condition necessary to give the silver its chemical power; but the case is widely different, the communication must be not only conducting, but metallic, and even then no chemical effect will be produced, unless the extremities of the wires are immersed in the same liquid, or in two separate portions of liquid that have a conducting communication with each other.

182. Place two glasses filled with a solution of copper near each other. Make a compound arc, by twisting together the end of a wire of zinc, with the end of a similar wire of silver. Connect the two glasses by placing the silver leg of the arc in one, and the zinc in the other. The zinc will immediately attract copper from the solution, but it does not communicate that power to the silver, though they are both closely

connected. Whilst the compound arc remains, connect the two glasses by a second arc, formed of a piece of bent wire of any kind, except gold or platina. The silver will be immediately covered with a coating of copper, and will continue to separate copper from the solution as long as the disposition of the apparatus remains the same. Now the only difference in the arrangement, that appears to have operated as a condition to the chemical power of the silver, was the provision of another conducting communication between the glasses, in addition to that established by the compound are; it therefore appears, that the associated metals cannot serve as conductors to the effect produced; and indeed, if they did, it would be scarcely possible any accumulation of power could result from the increased number of plates in a Voltaic battery.

183. This experiment does not display any of the electric powers of a Voltaic combination; but it shows that the association of three different substances is essential to the chemical agency of such a combination; and the phenomena will be found to correspond with some experiments of M. De Luc, on the efficient groups in the Voltaic pile. This celebrated philosopher found that no chemical effects were produced by any Voltaic arrangements, unless two metals were employed with a liquid between them; and, in the experiment last described, zinc, silver, and a metallic solution were inactive, though in contact with each other, until the fluid was made the medium of conducting communication between the free extremities of the combined metals.

184. The experiment last described will succeed, when the two glasses containing the metallic solution, are connected by any moistened. conductor; but the chemical power of the silver wire will be evinced slower, in proportion as the length of the moistened conductor is increased; and in all experiments of the kind, the less the interval between the extremities of the compound arc, the more rapid is its action on the interposed fluid. Hence, in the arrangements of Voltaic apparatus, for the purpose of chemical decomposition, the ends of the conducting wires are placed at a greater or less distance from each other, in proportion as their action is required to be more or less intense.

185. The arrangement of a simple Voltaic combination, by Mr. Sylvester, in which this effect is apparent, may be referred to. It consists of a tall glass jar filled with very dilute muriatic acid. Through a cork, placed in the neck of this jar, two wires are inserted; the one a short straight wire of zinc, the other a long bent wire of platina, or silver; by turning this last round, its upper end may be brought in contact with the zinc, or separated from it at pleasure. When they are separate, the zinc only is acted on; but, as soon as they are brought in contact, the platina or silver becomes covered with bubbles of gas, which appear soonest, and are evolved in the greatest quantity, from the projecting point.

186. Notwithstanding this circumstance, the power of a simple Voltaic combination con

tinues to exert its effect, when the stratum of interposed fluid is considerable. If a tube of three feet long be filled with dilute muriatic acid, and a wire of platina be inserted through a cork in one of its extremities, and a wire of zinc in the other; on connecting the wires, gas will be soon evolved from the silver. If the tube be bent the effect will take place more slowly. Mr. Singer took two similar tubes of eighteen inches long, and connected them by a short piece of flexible pipe, so as to form together a tube of three feet in length, with a joint in the middle, which admitted of its employment either as a straight tube, or as a siphon with a bend of any required inclination. In the open ends of this tube he placed respectively a zinc, and a platina wire; and found that, whenever their outer ends were connected by a wire, hydrogen was soon evolved from the platina; but this effect took place soonest when the tube was straight, and hence it appears that the power put in motion by these combinations, can pass more readily through any given column of a fluid in a straight line, than in any other direction.

187. It has been seen, that, when any metal is in solution in the interposed fluid, it is revived by the wire which in other cases evolves hydrogen; and it has been shown, by the effect of the silver and the platina wire, that metals which have no chemical action on the interposed fluid alone, may decompose it when combined with another metal. These facts, though far from being perfectly understood, may serve to explain some chemical effects which were before rather obscure. If a zinc wire, for instance, be immersed in a solution of lead, the latter metal will be revived in the form of a metallic vegetation, which increases gradually by additions to its extremities. The first separation of the lead is sufficiently intelligible; the acid in which that metal is dissolved, having a stronger attraction for the zinc, dissolves a portion of it, and deposits on its surface an equal portion of lead. But the lead, so revived, continues to revive more, and to receive additions at its remote extremities, whilst it would have been rather expected these additions would have been made on the zinc, and the vegetation that had been first formed protruded further into the fluid by that means. The contrary result is now understood to be obtained, by the revived particles of lead forming a Voltaic combination with the zinc and the surrounding fluid. This effect is analogous to that which obtains in various other instances.

188. Spread a few drops of a solution of silver upon a pane of glass, and place a small piece of platina, and a similar piece of copper wire upon it, at a little distance from each other. A vegetation will take place about the copper wire; but no effect will be produced by the platina. Bring the wires in contact with each other, and the Voltaic combination thus formed will occasion a beautiful vegetation of metallic silver to surround the platina wire. :

189. With a solution of tin, and wires of zinc and platina, similar phenomena occur; but a considerable time elapses, after the contact, before the vegetation appears round the platina. The immediate contact of the oxidable metal

with the metallic solution is not absolutely necessary to the success of these experiments; it is only essential that a regular Voltaic circle, consisting of two different metals and a moist conductor be established.

190. If we take a glass tube having a piece of bladder tied over its lower extremity water tight, and a cork inserted in its upper end with a platina wire passing through it; and the tube be filled with acetate of lead, and placed in a small cup of zinc containing dilute muriatic acid; we shall find that, when a metallic communication is formed between this cup and the platina wire, the latter will become studded with brilliant crystals of metallic lead. In this case the oxidable metal has no connexion with the metallic solution but through the medium of the platina wire on the one side and moist bladder on the other.

191. Fill two similar glasses, the one with a solution of silver, the other with dilute muriatic acid; connect them by a compound wire arc of zinc and platina; the zinc being plunged in the muriatic acid, and the platina in the metallic solution. Immerse a second arc, formed of a bent silver wire, in the two glasses, one of its legs being in each; after some time the zinc wire will be entirely dissolved, and the platina will be found covered with minute crystals of metallic silver, displaying a very beautiful appearance under the microscope.

192. Copper and zinc are the metals most usually employed in the construction of Voltaic apparatus, for their effects are greater, in proportion to the value of the metals, than those of any other combination. Silver and zinc, or gold and zinc, would be more powerful, but not so much so as to compensate for the increased expense.

In

193. As the effects produced by a single pair of metals, of any size, are still exceedingly feeble, attempts were made to combine the action of several pairs. Professor Robinson arranged a series of zinc and silver plates, about the size of a shilling, so as to form a rouleau; and on applying his tongue to the edge of this, the sensation experienced was more manifest than by a simple pair of metals; but its power in other respects did not appear more considerable. this arrangement every zinc plate was necessarily between two silver plates, and every silver plate between two of zinc, with the exception of the first and last. Now it has been stated, that the contact of zinc with silver, or copper, occasions some electric fluid to flow from either of those metals to it; and, consequently, when a single pair of metals are associated, the outer surface of the zinc appears positive, and that of the silver or copper negative. But if both surfaces of the zinc are in contact with copper or silver, electricity will flow into it in contrary directions, so that neither surface can exhibit the effect; and the same circumstance occurs, in a contrary order, when both surfaces of a silver or copper plate are in contact with zinc. Hence every arrangement of this kind, however numerous the pairs of metal, will exhibit at its opposite extremities the powers of a single pair of metals only.

194. Volta had the penetration to ascertain the cause of this defect in the rouleau of professor Robison; and his ingenuity supplied a means of obviating it. His experiments on the combination of two metals with an imperfect conductor (as water or saline fluids) had taught him that the electro-motive power of these fluids interfered but little with the more powerful energy of the combined metals; and that in fact they acted principally as conductors to that erergy. He therefore interposed imperfect conductors of this kind between a series of pairs of metal, and thus combined their power without producing a counteracting current ;. for the zinc and silver, or zinc and copper, were then in contact with each other at one surface only, but the conducting communication existed throughout.

195. To construct an apparatus of this kind, procure a number of plates of zinc and copper, or zinc and silver, either round or square, of any size; and an equal number of pieces of cloth, leather, or pasteboard, of the same form, but rather smaller. Soak these last in salt water, until they are thoroughly moistened; place a plate of silver, or copper, upon the table, then upon that place a piece of zinc, and on the zinc one of the moistened discs; upon this a second series of silver, zinc, and moistened cloth (or pasteboard) in the same order; and thus consecutively until a series of fifty or sixty repetitions have been placed one upon the other. Particular care must be taken to place the plates in regular order; if in the first group silver is placed lowest, zinc next, and then the moistened disc, the same disposition must be observed through

out.

196. The Voltaic pile being thus formed, let the operator moisten both his hands with brine, and grasp a silver spoon in each. If the top of the pile be then touched with one spoon, and the bottom with the other, a distant but slight shock will be felt at every repetition of the contacts. This shock resembles very nearly the sensation produced by a very large electrical battery weakly charged; it is greater in proportion to the number of groups of which the pile is composed. If the communication is made with any part of the face near the eyes, or with a silver spoon held in the mouth, a vivid flash of light is perceived at the moment of contact, and that whether the eyes be open or shut.

197. The power of an apparatus of this kind continues for some time, but gradually diminishes, the zinc surfaces becoming oxidated by the action of the moisture; it therefore requires to be taken to pieces and cleaned, an operation that is very troublesome when the number of plates is considerable. This inconvenience was diminished by soldering each pair of zinc and copper plates together, instead of simply laying them on each other; and a further improvement was devised by Mr. Cruickshanks, which consisted in cementing the pairs of plates in regular order, in grooves made in the side of a mahogany trough, so as to form water-tight cells between each pair. These cells being filled with water, or any conducting fluid, served as a substitute for the moistened discs used in the pile; and, as the fluid could be easily poured out and replaced, it re

quired considerably less time to keep it in proper order. This form of the apparatus, which is called the Voltaic trough, or battery, has been much used in this country; it is perhaps, on the whole the best arrangement hitherto devised, and its construction is sufficiently simple.

198. The zinc plates are made by casting that metal in an iron or brass mould; they may be about an eighth of an inch thick. The copper need not exceed twelve or fourteen ounces to the square foot, and may be soldered to the zinc at one edge only, the other three being secured by cement in the trough.

199. The trough must have as many grooves in its sides as the number of plates it is intended to contain, which should be fewer in proportion to their size, otherwise the apparatus will be inconvenient from its weight. When the plates are not more than three inches square their number in one trough may be fifty, and the distance of the grooves from three-eighths to half an inch, The trough must be made of very dry wood, and put together with white lead or cement. The plates being placed to the fire, the trough is to be well warmed, and placed horizontally on a level table, with its bottom downwards, very hot cement is then to be poured into it, until the bottom is covered to the depth of a quarter of an inch. During this process the plates will have become warm, and they are then to be quickly slided into the grooves and pushed firmly to the bottom, so as to bed themselves securely in the cement. In this way the plates are very perfectly cemented at the bottom, and, when this cement is sufficiently cool, a slip of thin deal is to be slightly nailed on the top edge of one of the sides of the trough, so as to overhang the inner surface about a quarter of an inch. The trough being about three quarters of an inch deeper than the diameter of the plates, there will be an interval between their top edges and the deal slip; and, when the side of the trough to which the slip is attached is laid flat upon the table, this interval forms a channel into which very hot cement is to be poured, and it will flow between each pair of plates, so as to cement one side of all the cells perfectly. As soon as the channel is quite full of fluid cement, the strip of deal is to be torn off, and the trough inclined so as to admit the superfluous cement to run out. When this is effected, and the cement cool, a slip of deal is to be nailed on the opposite side and the same process pursued with that. The instrument will then be cemented in the most perfect manner, and it may be cleaned off and varnished.

200. We may notice the preparation of electrical cements. The various cements employed in the construction of electrical apparatus are formed principally of resin, with the addition of some substances to render it more adhesive, and less brittle. Five pounds of resin, one pound of bees'-wax, one pound of red ochre, and two table spoonfuls of plaster of Paris, when melted, and well incorporated together, form a very good cement for general purposes. One that is well adapted for cementing large Voltaic batteries, and which is cheaper, may be formed of six pounds of resin, one pound of red ochre, half a