Page images
PDF
EPUB

On rubbing together two metals connected with the ends of the galvanometer, the following order is observed, beginning with the metal which is negative with all others : Bismuth, nickel, cobalt, palladium, platinum, lead, tin, gold, silver, copper, zinc, iron, cadmium, antimony, This is the thermo-electric series. Nevertheless, Becquerel is of opinion (wrongly perhaps) that the production of electricity in this manner cannot be attributed to the heat developed by friction.—A button of bismuth, antimony, iron, or platinum, rubbed on a plate of the same metal, becomes positive; zinc likewise exhibits this action in a slight degree, Filings or granules of metal, as well as metallic oxides or sulphurets, let fall on a plate of the same metal placed in a slanting position, always become negative; eo likewise does rough glass when rubbed upon smooth. (Becquerel.)—To this class of effects belongs also the electrization of powders let fall through sieves made of different materials.

Finely-divided copper, obtained by reducing carbonate of copper by means of hydrogen gas at a very low temperature, becomes strongly electrical when pressed together,

Perfectly dry oxalate of lime becomes positively electrified, in so high a degree, merely by stirring it with a rod of glass or platinum (which at the same time becomes negative), that the powder is lifted out of the basin which contains it. (Faraday, Qu. J. of Sc., 19, 338.)

Sulphur, wax, tallow, cocoa, or chocolate, after fusion, and calomel after sublimation, left to cool in a glass or metallic vessel, shows no sign of electricity on its upper surface; but very strong electrization, often sufficient to give sparks, on the surface which has been in contact with the vessel. The electricity is generally positive; but with sulphur I have sometimes found it to be negative, whilst the inner surface of the vessel exhibits the opposite electricity in an equal degree. (Vid. Crell. Ann. 1784, 2, 119; 1786, 1, 325; Gilb. 23, 230; Kastn. Archiv. 6, 472.) These phenomena were formerly attributed to the existence of positive electricity in a state of combination in liquids, this positive electricity being supposed to be set free on the passage of the body to the solid state. But since the positive electricity does not show itself on the upper surface of the solidified mass, but only where it is in contact with the vessel,- and since, according to Gay-Lussac (Ann. Chim. Phys. 8, 159), no negative electricity is set free during the fusion of metals in glass vessels,—which, however, ought to ensue if positive electricity were rendered latent during the liquefaction, it is better to suppose, with Gay-Lussac, that the electricity observed in this process proceeds merely from the friction occasioned by the unequal contraction of the solidifying body and of the glass vessel with which it is in contact, and from a partial separation resulting from the same cause.

The following experiments, however, cannot well be explained on such a supposition. When water is allowed to freeze in a Leyden jar, the inside of the jar becomes slightly positive, the outside slightly negative; the rapid deposition of ice in the form of hoar-frost produces the contrary effect. (Grotthuss, Ann. Chim. Phys. 27, 111.)-If a glass bulb and a tube about 0.01 or 0.02 metre long attached to it be completely filled with water, surrounded with cotton moistened with ether, and placed under the receiver of the air-pump, an electric spark, visible even by day, will dart out of the tube the moment before the liquid freezes. (Pontus, J. Chim. Med. 9, 430.)

The degree and kind of electricity which two bodies assume on being rubbed together vary with the temperature, the pressure, and the hygrometric state of the air. (Dessaignes, J. Phys. 82, 360 and 413; 83, 4, 194 and 415.)-A glass tube rubbed with a cloth perpendicularly to its axis becomes positive; but when pressed under the arm and rubbed backwards and forwards, parallel to its axis, it generally becomes negative. (Gm.)

According to Wollaston's view, friction-electricity always proceeds from oxidation: for, according to that philosopher, glass gives no electricity when rubbed with an amalgam of silver or platinum, because these metals are not oxidable. It is more powerfully excited by zinc-amalgam than by tin-amalgam, because the former is the more oxidable; and still more strongly by a mixture of the two, which oxidates most quickly of all. According to Wollaston, also, an electrical machine gives no electricity when made to work in carbonic acid gas. But, according to Gay-Lussac, electricity is obtained in carbonic acid gas when the gas is dry; according to Sir H. Davy, it is also obtained in hydrogen gas, and more abundantly in carbonic acid gas than in the air; and, according to Peclet (Ann. Chim. Phys. 70, 83), the electric excitement is equally strong in dry air, carbonic acid gas, and hydrogen gas.

On the development of electricity by friction depend the Electrophorus and the Electrical Machine, which yield electricity of the greatest tension, i.e. accumulated in the greatest quantity on a given surface. H. Development of Electricity by Chemical Changes in Ponderable Bodies:

Chemical Electricity.

a. By Chemical Combination. During the combination of two substances, a very small quantity of electricity often shows itself in them. In oxygen which combines with combustible bodies, and in acids which combine with salifiable bases, the electricity is positive; in combustible bodies and salifiable bases it is negative.

[Oxygen contains positive electricity in a state of combination, combustible bodies negative electricity. When these ponderable bodies combine, their opposite electricities also come together in the form of fire; but under certain circumstances, a very small quantity of them appears to remain uncombined, so that a trace of positive electricity shows itself on the side of the oxygen, and a trace of negative electricity on the side of the combustible body: This is also Pouillet's view, as far as combustions are concerned.

Similarly, with acids and salifiable bases.] To render this feeble electricity sensible, one of the bodies must be placed in connection with the upper plate of the condenser of a Bohnenberger's electroscope, and the other with the ground; or else the two bodies must be respectively connected with the two ends of the galvanometer.

When coals are burnt in the air, negative electricity accumulates in the vessel in which the combustion takes place. (Lavoisier & Laplace.) An insulated stove in which a strong coal fire is burning, becomes negative; the electricity is strongest at each addition of fuel. (Williams, Phil. Mag. J. 18, 93.)

If a cylinder of charcoal, burning only at the upper end, be placed on the cover of the condenser, negative electricity soon accumulates in the condenser; to a still greater degree when the combustion is fed with oxygen gas. If the burning cylinder be connected with the ground, and a metal plate communicating with the cover of the condenser be held

over it at the distance of a few inches or a foot, the condenser will become positively electrical. If the charcoal cylinder burning at one end be laid horizontally, or if it be placed upright and made to barn at the side instead of on the top, no electricity will be perceptible, because the negative electricity of the charcoal will be neutralized by the positive electricity of the surrounding air. (Pouillet.)

When hydrogen gas issuing from a metal tube is set on fire, the cover of a condenser connected with the tube becomes negative. If the tube be connected with the ground and a metal plate held at some little distance above the flame, the plate conveys positive electricity to the plate of the condenser. When the hydrogen issues from a glass tube, negative electricity is obtained by introducing into the middle of the flame a narrow coil of platinum wire connected with the condenser; but if the coil be wide enough to surround the flame without touching it in any part, the electricity will be positive. A metal plate held over the flame does not become electrical when the gas is burned from a glass tube,–because the glass insulates, and consequently, the two electricities neutralize one another within the flame. The flame of alcohol, ether, oil, tallow, or wax, exhibits the same effects as that of hydrogen gas. (Pouillet.) In the combustion of alcohol in the lamp without flame, negative electricity also accumulates in the spiral wire, and positive electricity in the surrounding air. (Becquerel.)

Pfaff (Pogg. 51, 110) regards these statements as erroneous, and asserts that not a trace of electricity is apparent in the combustion of hydrogen gas, phosphorus, sulphur, zinc, alcohol, or ether; only in the combustion of charcoal is there an indication of negative electricity; but as no positive electricity cau be detected in the carbonic acid which rises from it, he regards the phenomenon as proceeding from thermo-electricity.

A thin copper tube through which à dry mixture of chlorine gas and air is passed becomes negative; the gas subsequently transmitted through a platinum tube renders it positive.

On connecting the ends of the galvanometer with two iron wires, a and 6, inserting a into a piece of charcoal, then heating to redness both the charcoal with the end of the wire a enclosed in it, and also the extremity of the wire b, and connecting the latter with the charcoal, a strong current will pass from the wire b through the galvanometer to the wire a; hence, in this case, the carbon acts the part of oxygen si.e. in its combination with the iron of a, positive electricity is set free in it, and negative electricity in the iron]. (Becquerel.)

For the investigation of the development of electricity in the combination of two liquids, or of a liquid and a solid, the pieces of apparatus represented in Plate IV are useful.

App. 1. A platinum spoon containing a liquid is connected with one end of the galvanometer. With the other end is connected a pair of platinum forceps, in which a solid body can be fastened so as to dip into the liquid.

App. 2. Two cups or beakers a, b, into which are plunged the platinum terminations of the galvanometer, contain two different liquids wbich are connected with one another, either by a bunch of asbestus or cotton-threads, or by means of a siphon, filled, sometimes with one of the liquids, sometimes with a liquid different from both.

App. 3. A beaker glass is cut in halves in a vertical direction, and after a sheet of bibulous paper has been inserted into it, bound tightly together again. Into the two divisions formed by the paper partition two different liquids are poured, and the platinum ends of the galvanometer dipped into them.

App. 4. The lower part h of a U-tube is stopped up with cotton, asbestus, or clay, moistened with a suitable liquid; then the arm a is filled with this same liquid and the arm b with another.

App. 5. The extremity b of the U-tube being stopped with the finger, the arm a is filled with the heavier liquid; the end a is then closed, the end b opened, and the lighter liquid carefully poured in at this end, so that it may dispose itself in a separate stratum above the heavier liquid.

App. 6. A hole having been made in the bottom of a beaker-glass, and one of the platinum ends of the galvanometer cemented into it, the two liquids are carefully introduced into the glass, oue above the other, and the other platinum

termination made to dip into the upper liquid. App. 7. A glass tube a has its lower extremity either tied round with a bladder or stopped up with clay moistened with a liquid. It contains a liquid, and dips with its lower end into another liquid contained in the beaker 6. Into a and b the platinum ends of the galvanometer are made to dip.

App. 8. Two glass tubes a, b, closed at the bottom with bladder or moistened clay, are filled with different liquids; and made to dip by their lower ends into the liquid in the dish c.

Acids with Acids. The platinum spoon (App. 1) containing oil of vitriol, and the spongy platinum in the forceps, nitric acid, positive electricity goes in considerable quantity from the oil of vitriol through the galvanometer to the nitric acid. If the oil of vitriol be previously diluted with one-half water a strong current is set up in the opposite direction. In the former case, the action of the oil of vitriol on the water of the nitric acid probably comes into play. (Becquerel.) — From oil of vitriol (4 pp. 2) positive electricity passes in small quantity through the galvanometer to nitric acid. (De la Rive.)-Positive electricity goes from phosphoric acid, through the galvanometer, to sulphuric, hydrochloric, or nitric acid; negative from nitric to hydrochloric, hyponitric, or acetic acid. (Becquerel.)— Positive electricity

goes from oil of vitriol, through the galvanometer, to concentrated hydrochloric acid (App. 2 or 7); on the contrary, from concentrated nitric acid to oil of vitriol (App. 2 or 7). Walcker.- Positive electricity goes in large quantity from slightly diluted oil of vitriol through the galvanometer to nitric acid. (App. 5.) Mohr.

Concentrated Acids with dilute Acids.' From concentrated sulphuric or hydrochloric acid, positive electricity goes through the galvanometer to the same acids in a state of dilution. (App. 2 or 7.) Walcker.-From concentrated nitric acid, a feeble current passes through the galvanometer to dilute nitric acid, diminishing in intensity as the 2 liquids are moved about at their surface of contact. (App. 5.) Faraday.

Acids with Water. From concentrated sulphuric or nitric acid contained in the spongy platinum in the forceps (App. 1), positive electricity goes through the galvanometer to water in the platinum spoon,-weak at first, but continually becoming stronger, as the water by taking up acid becomes a better conductor,—then gradually diminishing in force, till the liquids have become completely mixed, when it stops. With hydrochloric acid and water, the current takes the opposite direction; so likewise with boracic, oxalic, and citric acid, which are fixed in the forceps in the solid state. (Becquerel.)—With sulphuric acid and water or ice, positive electricity passes from the water through the galvanometer to the acid. (Nobili.)

Acids with Salts. Positive electricity goes from phosphoric acid, through the galvanometer, to solutions of all salts; from nitric acid to solutions of sulphates, chlorides, and nitrates (Becquerel);– from nitric acid to solution of nitre. (H. Davy).-Positive electricity goes from sulphuric acid, through the galvanometer, to the sulphates of potash, copper, and red oxide of mercury; from hydrochloric acid to chloride of potassium, sodium, barinm, or calcium, and from nitric acid to nitre: always therefore from the acid through the galvanometer to the salts of the same acid; positive electricity also goes from hydrochloric acid through the galvanometer to sulphate of magnesia or nitre. (Nobili.) - The current goes from dilute sulphuric acid through the galvanometer to sulphate of zinc or copper, and from concentrated nitric acid to sulphate or nitrate of copper. On the contrary, from chloride of mercury to oil of vitriol, from nitrate of silver to acetic acid, and from chloride of gold to hydrochloric acid. (App. 2 or 7.) Walcker.

A cids with Salifiable Bases. Positive electricity goes from dilute sulphuric, hydrochloric, or nitric acid, contained in the platinum spoon, (4 pp. 1) through the galvanometer, to moistened hydrate of potash in the forceps. Similarly, from dilute acids to aqueous solution of potash (App. 2, with asbestus.) Becquerel.—Walcker also obtained a strong current from the acid (but probably through the galvanometer?) to the potash. Faraday, on the other hand, obtained no current with dilute sulphuric acid and aqueous solution of potash (A pp. 3); Mohr also obtained with dilute sulphuric or hydrochloric acid, on the one side, and aqueous solution of potash or ammonia on the other, either no current at all, or merely a slight disturbance of the needle at the commencement of the action; whereas, he found that from concentrated or dilute nitric acid, positive electricity goes through the galvanometer to the potash.

From sulphuric or nitric acid, positive electricity goes through the galvanometer to aqueous solution of ammonia (Nobili); from dilute sulphuric acid to aqueous ammonia, soda, or baryta (App. 2 or 7) Walcker; from sulphuric, hydrochloric, or nitric acid, through the galvanometer, to solid Iime; but, on the contrary, from lime-water through the galvanometer to the acid. It also goes from solid lime through the galvanometer to aqueous solution of arsenic, oxalic, or tartaric acid, and from aqueous ammonia to oxalic acid. (Nobili.)

If hydrated phosphoric acid be fused in one arm of the U-tube, (App. 5) and hydrate of potash or oxide of lead in the other, positive electricity goes from the acid through the galvanometer to the base (especially with potash) in sufficient quantity to produce a slight decomposition of iodide of potassium. (Dulk & Moser, Pogg. 42, 91.)–From nitric acid, positive electricity goes through the galvanometer to oxide of lead. (Faraday.)

Salts with Water. When sulphate of soda or chloride of barium is dissolved in water, a feeble positive current goes from the water through the galvanometer to the salt. (Becquerel.). From a solution of nitrate of silver in 12 times its weight of water positive electricity goes through the galvanometer to pure water. (Fechner.)

Concentrated with dilute saline solutions. Positive electricity goes from a concentrated solution of common salt or nitre, through the galvanometer, to a dilute solution of the same. (A pp. 2.) Becquerel; also from dilute to concentrated solution of liver of sulphur, through the galvanometer. (Faraday.)--If two platinum spatulas, one cold and the other red-hot, be dipped into the same solution of 1 part of common salt in 10 parts of

« PreviousContinue »