to tha enome

er from alkalis, on the contrary, we might expect ity, which the water had lost by its previous alkali, would be again taken up by the

aqueous

alkali would again take up negative electricity, so ricity would be set free in the vessel: this, however, is

ith the statements of Becquerel and Fechner (p. 332). It is e that all salts, even those which are very alkaline, like carof potash, behave in this respect like acids].

No electricity is developed in the evaporation of pure water, not even when it is dropt into a red-hot platinum crucible in which Leidenfrost's phenomenon is produced, followed by rapid boiling. (Becquerel; Schweigger, Schw. 44, 171; Pouillet; Peltier). Similarly, with the most highly concentrated sulphuric or nitric acid and glacial acetic acid.— When the water contains potash, soda, baryta, strontia, or lime in solution, the vessel constantly becomes positive, feebly during the continuance of Leidenfrost's phenomenon, strongly during the subsequent boiling. With solution of ammonia, the vessel becomes negative, because in this case it is principally the ammonia which evaporates, while the water remains. If the water contains only sulphuric acid, glacial acetic acid, or any other acid, or any carbonate, sulphate, chloride, nitrate, or acetate, the vessel becomes negative. Hence, the electricity of the atmosphere may in great part be attributed to the evaporation of seawater, and other kinds of water not quite pure, on the surface of the earth, and in the bodies of plants and animals. When pure water evaporates in vessels of iron, copper, or silver containing copper, the vessel becomes negative from commencing oxidation, even when the water contains an alkali in solution. (Pouillet.)

Peltier remarked that in the evaporation of a solution of common salt, negative electricity was perceptible only at the moment when the remaining salt began to decrepitate, an effect which also takes place on the decrepitation of crystals of common salt thrown into a red-hot platinum crucible. Hence, according to Peltier, the electricity does not become apparent till the last portions of water separate from the salt.

Vapour escaping from boilers often exhibits positive, and the boiler negative electricity. If one hand, or a plate of metal, or a bundle of wires with numerous points, be held in the stream of vapour, and the other brought near the boiler, a spark may often be obtained from the latter. The higher the pressure, the stronger is the electricity. The cloud of steam which collects under the roof of the building also contains electricity. If the boiler be cleaned from the incrustation, chiefly consisting of gypsum, which lines it, and fed with rain-water, no electricity will be developed: with spring-water, the electricity will not be apparent at first-not in fact till a sediment has been formed; and as this increases, the development of electricity will increase also. (Armstrong.)

By experiments made with a boiler of gun-metal, 30 inches long, 4 inches wide, heated with coke in an insulated furnace, and furnished with a glass tube and stop-cock to regulate the escape of the vapour, the following results were obtained. When the vapour is allowed to escape with the safety-valve open, that is to say, at the ordinary atmospheric pressure, no electricity is apparent; but at 1 lb. pressure per square inch, the electricity begins to show itself. At 3lb. pressure, the boiler gives a spark after the steam has been escaping for a minute. At 15 lb. pressure,-if the stop-cock be so turned that the quantity of vapour escaping

in a given time shall remain the same,-the quantity of electricity be comes double; at 50 lb. pressure, treble; at 120 lb. quadruple, and 250 lb. quintuple of what it was at 3 lb. pressure. At 100 lb. pressure a Leyden jar, the knob of which is held in the jet of vapour, while its outer coating is connected with the boiler or furnace, becomes charged in two minutes; the apparatus may therefore be used as an electrical machine. The vapour is generally positive, the boiler negative. These conditions are seldom reversed; and even when they are, the electricity first becomes apparent at a pressure of 1 lb., and increases, as the pressure rises to 30lb. in the same ratio as in the former case; but at a still higher pressure, the boiler exhibits negative electricity during the first few minutes of the escape of the vapour, and positive afterwards. When an almost empty boiler is heated till all the water is converted into vapour, the boiler also becomes electrified, on the escape of the vapour, and its electricity negative. From this it would appear that the development of elvtricity is due, not so much to the formation of the vapour, as to its precipitation by the cold air (or to its expansion, Gm.?).-The oftener the boiler is used, the more does it become inclined to assume a positive charge; so that at last the vapour almost always exhibits negative electricity. In this case, the inside of the boiler is not found to be oxidated in the slightest degree, and its tendency to become positive is not destroyed by washing it out. But if a very small quantity of potash or soda be added to the water in the boiler (lime does not act so strongly), the vapour once more becomes so strongly positive [vid. Pouillet's experiments, p. 337] that it will give thirty sparks, half an inch long, in a minute. A very small quantity of nitric acid or sulphate of copper makes the vapour negative. Hydrochloric acid, sulphuric acid-either alone or mixed with iron filings and common salt, produce no effect.

¶ Faraday has shown that electricity is never excited by the passage of pure steam, and is manifested only when water is likewise present. Hence he concludes that the effect is altogether due to the friction of the globules against the sides of the opening, or against the substances opposed to its passage, as the water is rapidly moved onwards by the current of steam. Accordingly, it was found to be increased in quantity by increasing the pressure and impelling force of the steam. The immediate effect of this friction was, in all cases, to render the steam positive, and the solids, whatever they might be, negative. In certain circumstances, however, as when a wire is placed in the current of steam at some distance from the orifice, the solid exhibits the positive electricity acquired by the steam, of which it is then merely the recipient and conductor. In like manner, the results may be greatly modified by the shape, nature, and temperature, of the passages through which the steam is forced. Heat, by preventing the condensation of the steam into water, likewise prevents the evolution of electricity, which, however, speedily appears on cooling the passages, so as to restore the water which is necessary for the production of that effect. The phenomenon of the evolution of electricity in these circumstances is dependent also on the quality of the fluid in motion, more especially in relation to its conducting power. Water will not excite electricity, unless it be pure: the addition of any soluble salt or acid, even in minute quantity, is sufficient to destroy this property. The addition of oil of turpentine, on the contrary, occasions the development of electricity of the opposite kind to that which is excited by water; because each particle of the water becomes covered with a

C

at the friction takes place only between that external s along whose surface the globules of liquid are carbut more permanent effect is produced by the presence hich is not, like oil of turpentine, subject to rapid dissipaerimental Researches, Series 18; abstr. Phil. Mag. J. 22, 486. so Armstrong, Phil. Mag. J. 22, 1.) ¶

Pfaff found (Pogg. 53, 313) that the vapour issuing from a Papin's gester was positive, and the digester itself negative-even when the water contained potash, carbonate of potash, sulphuric acid, or common salt-the strength of the charge increasing with the tension of the vapour; he also obtained more electricity on holding the metal plate in the vapour at some inches distance from the tube, than when he held it closer. Williams (Phil. Mag. J. 18, 93) also found the boiler negative.

When air is compressed in a metallic vessel to eight times its ordinary density, the vessel generally becomes negative when the stop-cock is opened, and gives sparks a quarter of an inch long, whilst the air which escapes shows positive electricity. More electricity is obtained when the vessel is cold and damp, than when it is warm and dry. A perfectly dry vessel ceases to show signs of electricity even when moderately heated, a damp one not till it is heated strongly; but in the cold, dampness does not seem to increase the electricity. (Armstrong.) [Since the experiment was made with air not perfectly dry, it is possible that water may have been deposited during its compression, and after combining with impurities in the vessel, may have been again converted into vapour on the escape of the air. A repetition of these experiments with dry air is therefore desirable, in order to ascertain whether the electricity proceeds from chemical or mechanical causes.]

If a mixture of water and peroxide of hydrogen be placed in a platinum spoon connected with the galvanometer (App. 1), and a piece of spongy platinum, gold, or silver, or even finely-divided ignoble metals, also connected with the galvanometer, be dipped into the liquid,-oxygen gas will be evolved from the peroxide of hydrogen, and positive electricity will pass from the spoon, through the galvanometer, to the spongy metal. If, on the contrary, oxide of silver or hydrate of potash, wrapped up in moist paper and held in the forceps, be dipped into the liquid, an opposite current will be produced. (Becquerel.) [In the first case, oxygen gas is evolved on the surface of the spongy metal,-in the second, on the platinum spoon, and renders it negative by removing its positive electricity. The water which has lost its oxygen takes up negative electricity, and sets positive electricity free.]

Since, in the combination of carbon with oxygen, the former exhibits negative, the latter positive electricity (p. 329),-it is probable that when carbonic acid is decomposed by plants, under the influence of light, into carbon which is retained by the plants, and oxygen which is set free, the plants will exhibit positive electricity. When seeds are suffered to germinate in mould contained in twelve isolated pans, and the mould in all the pans is connected by a metallic conductor with the condenser of the electrometer, no electricity is perceptible during the first two days of germination; but afterwards, when the plants are more advanced, negative electricity shows itself both in the day-time and at night. In two instances only did the negative electricity gradually diminish, and give place to feeble positive electricity, which continued during the remaining time of the growth. (Pouillet.) [Can the slow combustion of the vegetable mould,

which must have generated negative electricity, have counteracted the regular development of the positive electricity?-J. Blake (Phil. M J. 12, 540) found that-on immersing the leaf of a plant in water, in such a manner that the stalk projected above the liquid, and connecting one end of the galvanometer with the stalk, and the other with the lamina-positive electricity passed from the stalk through the galvanometer into the lamina; the current was stronger in the light than in the dark, but always in the same direction. [This accords with Pouillet's supposition.]

C. Combinations accompanied by Decompositions.

a. In Imperfect Conductors.

Electricity in Detonations. In the decomposition of oxalate of silver by heat (whereby it is resolved with a hissing noise into silver and carbonic acid gas) a large quantity of electricity is set free; not, howeve when the salt is covered with a watch-glass. Oxalate of suboxide of cury, oxalate of copper and ammonia, and fulminate of mercurvshow but little electricity when decomposed by heat. (Dobereiner, Gill o7, 232.)

Fulminate of silver, when exploded by oil of vitriol or by the burning-glass, charges an electrometer on which it is placed, positively. If the decomposition is effected by means of an insulated iron wire heated to redness, positive electricity becomes apparent in a few instances,more frequently, feeble negative electricity, or none. If the salt is placed in a red-hot platinum spoon, either feeble negative electricity becomes apparent, or none.-Oxalate of silver decomposed by red-hot iron yields positive electricity when it is sifted on a heated platinum spoon. The spoon shows positive electricity if it be strongly ignited, none if heated to faint ignition, negative when still less heated, and none when still colder, but hot enough to decompose the salt with a hissing noise. When oxalate of silver is placed under a watch-glass on the cap of the electrometer, and exploded by a burning-glass, no electricity is developed; but on removing the watch-glass, negative electricity becomes apparent. If the oxalate of silver be exploded on the electrometer by means of a burning-glass, whilst a sheet of tinfoil connected with another electrometer is held at a short distance above it, the first electrometer will show negative, the second positive electricity. Oxalate of suboxide of mercury exploded by a red-hot wire, communicates a strong negative charge to the electrometer.-Oxalate of copper and ammonia, gunpowder, and a mixture of sulphur and chlorate of potash, give no electricity when exploded. (Schweigger.)

By heating certain salts in a platinum crucible connected by a wire with a Bohnenberger's electroscope, till they either explode or decompose with a hissing noise, and removing the spirit-lamp as soon as this decomposition begins, the following results are obtained. Oxalate and citrate of silver give strong, oxalate of copper and ammonia, weak negative electricity. No electricity is manifested by fulminating gold, fulminate of silver, oxalate of suboxide of mercury, and carbazotate of potash, soda, or baryta. (R. Böttger.) Pfaff likewise obtained negative electricity with oxalate and citrate of silver.

Electricity accompanying Decomposition by Simple Affinity. From the first-named substances in the following list, positive electricity goes through the galvanometer to the last-named. From sulphuric acid to nitrate of baryta, and from sulphate of magnesia to potash. (Becquerel.)-From sulphuric, nitric, or hydrochloric acid, to carbonate of lime, potash, or

soda; from carbonate of lime to oxalic acid; from sulphuric or nitric acid to chloride of potassium (strong); from sulphuric acid to chloride of barium. (Nobili.)-From oil of vitriol to solutions of common salt, acetate of baryta, or acetate of lead; from concentrated solution of sulphate of alumina or blue vitriol, to ammonia; from nitrate of silver to hydrochloric acid; from perchloride of iron to concentrated or dilute sulphuric acid, am

nia, or potash. (Walcker.)—For complicated cases with App. 10, vid. Fechner (Pogg. 48. 1 and 225).-In the decomposition of calomel by nitric acid, positive electricity goes from the acid through the galvanometer to the calomel. (De la Rive.) When carbonate of potash is decomposed by dilute sulphuric acid in a metallic vessel standing on the electrometer, the instrument shows a negative charge. (Lavoisier & Laplace, Crell, Ann. 1788, 1, 351). [I have also obtained negative electricity].

Electricity in decompositions by Double Affinity. Positive electricity goes from green vitriol through the galvanometer to ferrocyanide of potassium; from tincture of galls to green vitriol. (Becquerel.)-From alkaline sulphates to nitrate of baryta. (Nobili.)-From chloride of barium to carbonate of soda; from chloride of calcium to sulphate of copper; from perchloride of iron to hydrosulphuret of ammonium or ferrocyanide of potassium; from sulphuret of copper to carbonate of soda or ferrocyanide of potassium; from nitrate of silver to common salt, acetate of potash, or ferrocyanide of potassium; from chloride of gold or platinum to ferrocyanide of potassium. (Walcker.)-For complicated cases with four vessels, vid. Fechner.

Electricity in Fermentation. If two horizontal metal plates connected with the galvanometer be immersed in fermenting beer-wort, one at the bottom of the vessel, the other near the surface of the liquid, positive electricity proceeds, at first-so long as the yeast remains at the bottomfrom the lower plate through the galvanometer, to the upper; afterwards when the yeast rises to the surface, the current takes the opposite direction. Hence it appears that negative electricity always proceeds from the yeast (on which the bubbles of carbonic acid gas are evolved.)—J. Blake (Phil. Mag. J. 12, 539.)

B. In the Action of Perfect on Imperfect Conductors.

SIMPLE GALVANIC CIRCUIT.

1. Two Metals and one Liquid.

When two metals are placed in contact with an imperfectly conducting compound liquid, and connected together at some point within or without the liquid, either immediately or by means of a good conductor (a wire), and moreover, one of these metals has the power of decomposing the liquid by appropriating one or more of its elements, whilst the other is either destitute of this power or possesses it only in a less degree, then (1). Decomposition takes place, and a new compound is formed on the first metal only; whereas the second, if placed alone in the liquid, would in many cases exert a decomposing action upon it, and deprive it of the very elements which are actually taken from it by the first metal; (2). The decomposition goes on more quickly than it would, if the first metal were placed alone in the liquid. (3). Those elements of the liquid which are set free by the abstraction of the others, do not make their appearance at the surface of the first metal, where the action takes place, but at the surface of the second. (4). This action is invariably accompanied by a powerful electric current; and, when the first metal takes from the liquid,