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quantity of positive, and potassium of negative electricity. Bodies lying between these two extremes contain a larger quantity of heat with a smaller excess of one or the other kind of electricity, the proportion of which varies greatly according to their nature,—and thus form an electrical series which perhaps coincides with the column of affinity of oxygen (p. 144).

The combination of two ponderable bodies is the result of two forces, viz., the affinity of the ponderable bodies for each other, and the affinity of the electricity which is in excess in the one body for the opposite electricity which predominates in the other. By these two forces the affinity of the electro-negative body for the positive electricity united with it, and that of the electro-positive body for the negative electricity combined with it, are overcome. The result is heat and the ponderable compound. The latter retains the excess of positive or negative electricity, by which it acquires either an electro-negative or electro-positive character, and likewise part of the heat—while another portion is set free, and gives rise to the development of heat or fire, by which most chemical combinations are accompanied. When combination takes place between two bodies, both of which contain an excess of the same kind of electricitye. 9., oxygen and sulphur, which contain free positive electricity in different quantities--it is simplest to suppose that the combination is the result merely of the affinity between the two ponderable bodies, that the new compound contains the sum of the excesses of positive electricity, and that the development of heat is a consequence of the inability of the new compound to retain as much heat united with it as was before combined with its constituents.

When a ponderable compound is decomposed by elevation of temperature~e.g. oxide of silver at a red heat into oxygen gas and silver--it may be supposed that the affinity of silver for negative electricity + that of oxygen for positive electricity + that of heat for oxygen is greater than the affinity of silver for oxygen + that of the two electricities for each other. Hence part of the heat is resolved into its elements and unites as negative electricity with the silver and positive with the oxygen (Sch. 101). The decompositions of ponderable compounds by ponderable substances may perhaps take place as follows. When chlorine at a red heat expels oxygen from potash, forming chloride of potassium, it transfers that portion of positive electricity, which in combining with pure potassium it would have given up to the negative electricity of that substance -to the oxygen which has lost its own positive electricity by combining with the potassium (Sch. 102).-When potassium in contact with water produces potash and hydrogen gas, the negative electricity of the potas"sium goes over to the disengaged hydrogen, which in forming water had previously given up its own negative electricity to the positive electricity of the oxygen (Sch. 103). The same takes place in the solution of zinc in dilute sulphuric acid: its negative electricity goes over to the escaping hydrogen gas (Sch. 104). (For the explanation of the decomposition of compounds by the electric current according to this hypothesis, vid. Electricity.]

2. Dynamic II ypothesis. A substance which to our senses appears continuous, like glass, is likewise so in reality: it does not therefore consist of atoms and empty spaces, but fills completely the space included between its surfaces. Matter is therefore capable of expanding and contracting by virtue of its

own intrinsic nature, not in consequence of the widening or narrowing of pores contained within it. In chemical combination, the elements have the power of diffusing themselves through each other without limit, so that in the smallest point of the compound both elements are alike present;—the elements do not lay themselves side by side-they penetrate each other.

A. Kant's Theory. Matter is a self-existent essence, and is actuated by two forces, the force of attraction and the force of repulsion. It may indeed be pressed together by external force, but only to a certain point,-for its repulsive force increases with the condensation. The action of different kinds of matter on each other, whereby through their innate forces they alter the combination of each other's parts, is chemical action; it consists sometimes in solution, sometimes in decomposition. A perfect solution would be such as, in its smallest particles, would contain the heterogeneous substances in the same proportion as in the whole. Kant however leaves it undecided whether such a solution is ever actually formed; but it may be imagined--for if the action of the solvent power be continued, the division must still go on and that without limit, so that ultimately the volume of the solution will be uniformly filled with each of the two elements at the same time, and thus they will have penetrated each other. (Kant, Anfangsgr. d. Naturwissenschaft. Aufl. 3, s. 75.)

B. Schelling's Theory. Matter is not an original essence, but derives its origin from the conflict of the attractive and the repulsive force; and its various qualities depend upon the quantitative relation of these primary forces. Chemical action takes place only between heterogeneous bodies, those namely, in one of which the relation between the primary forces is the reverse of that in the other. The resulting compound is the mean dynamical ratio of the primary forces which have been brought into activity during the process, and consequently its properties differ essentially from those of its elements. (Schelling, İdeen zu einer Philosophie der Natur. Aufl. 2, 1803, s. 453.)

[Faraday: Speculation concerning the Nature of Matter. Phil. Mag. J. 24, 136.)

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THE Imponderable Bodies, Imponderables, Ethereal Substances, Radiant Powers, or Incoercibles, are distinguished from ponderable substances chiefly by the following characters.

1. They are without weight, so far at least as our balances can show.

2. They are in the highest degree expansible,—and therefore when unequally distributed diffuse themselves—for the most part quickly and by radiation in straight lines—through those spaces which offer no opposition to their progress.

3. They penetrate bodies which are impenetrable to all ponderable substances.

4. Generally speaking, they manifest themselves directly to but few of our senses; magnetism to none, light and heat to one, only electricity alone to several.

The properties here noticed certainly render it doubtful whether the sensations of light, heat, &c., should be attributed to the direct action of peculiar kinds of matter, or whether they are not rather caused by the vibrations of certain supposed elastic fluids of extreme tenuity, like the luminous ether, &c.; the former supposition is however the simpler of the two, and better adapted than the latter to a chemical view of the subject. According to the undulatory theory, the coloured rays of light are distinguished from one another by the different breadths of the waves of the luminous ether; and when they all fall on the eye together, they produce the sensation of pure colourless light. How different would be the impression produced by the whole series of sound-waves if they were all to invade the ear at once!

The Imponderables are: Light, Heat, Electricity and Magnetism :As these substances are all fully discussed in physics, we shall in this work confine ourselves principally to the chemical relations of the first three towards ponderable bodies, -omitting magnetism, which appears to exert no influence on the chemical relations of ponderable bodies.

CHAPTER I.

L I G H T.

On Light in general, and its relations to Heat. C. W. Scheele: Von der Luft und dem Feuer. Ups. and Leipz. 1777. p.

61, also Opusc. 1, 21. Herschel, on the Heating and Illuminating Powers of the Coloured Solar

Rays. Phil. Trans. 1800, II, 255, 292; III, 437; also Gilb. 7, 137;

10, 68; 12, 521. Karsten, on the Solar Rays. Scher. J. 7, 663. C. W. Böckman: Ueber die Erwärmung verschiedener Körper durch die

Sonnenstrahlen. Karslr. 1811. Seebeck, on the Heat of Prismatic Rays. Schw. 40, 129. Flaugergues, on the Heating Power of the Sun during a Solar Eclipse.

J. Phys. 92, 435. Baden Powell, on Solar Light and Heat. Ann. Phil. 23, 322 and 401; 24, 81 and 287; 25, 201.

On Terrestrial Light and Heat. Ann. Phil. 24, 181; 25, 201. Bérard, on the Physical and Chemical Properties of the Rays of Solar

Light. Report thereupon by Berthollet, Chaptal, and Biot. Gilb. 46, 376.

On the Chemical Action of Light. Ritter, on the Chemical Rays of Light. Gilb. 7, 527; 12, 409. Wollaston, on certain Chemical Effects of Light. Gilb. 39, 291. C. W. Böckmann, on the Action of Light upon Phosphorus. Scher. J.

5, 243. A. Vogel, on the Action of Light upon Phosphorus. Schw. 7,95; 9, 236. . Gay-Lussac & Thénard, on the Chemical Action of Light. Schw. 5, 219. Seebeck, on the Chemical Action of Light: in Göthe zur Farbenlehre, 2,

716;-likewise Schw. 2, 263; 7, 119. Bischof, on the Action of Light on a Mixture of Chlorine and Hydrogen

Gases : in his Lehrb. d. reinen Chemie, 1, 93; Kastn. Archiv. 1, 443. Grotthuss, on the Chemical Activity of Light. Gilb. 61, 50;-in detail in

his Phys. Chem. Schriften, 1, 1. G. Succow. Die Chemischen Wirkungen des Lichts. Darmst. 1832;-also

Pogg. 32, 287. G. Langrebe. Ueber das Licht, vorzugsweise über die Chemischen und

Physiologischen Wirkungen desselben. Marb. 1834. Dulk, on the Chemical Action of Light. J. pr. Chemie. 3, 225. Hessler, Chemical Action of Refracted Light. Zeitschr. Phys. Math. 3,

336. Chevreul. Action of Light on Coloured Tissues. Ann. Chim. Phys. 66,

71. Malaguti

. Chemical Effects of Light passing through various Fluids. Ann. Chim. Phys. 72, 5; abstr. Pogg. 49, 567. Draper. Chemical Action of Light. Phil. Mag. J. 16, 81; 24, 169.

VOL, I.

M

Hunt, on the same subject. Phil. Mag. Ann. 16, 138, and 268; Further,

Phil. Mag. J. 24, 96; 26, 25 and 276.

On the Daguerrotype: Arago. Ann. Chim. Phys. 71, 313; also Pogg. 48, 193; also Ann. Pharm. 31, 216; also J. Pr. Chem. 18, 215 — Biot. Pogg. 48, 217.-Fyfe. Ed. N. Phil. J. 28, 205.—Hunt. Phil. Mag. J. 16, 270; 17, 260.–Draper. Phil. Mag. J. 17, 217.- Fizeau. J. Pharm. 26, 581.-Herschel. Phil. Mag. J. 22, 120.-Claudet. Phil. Mag. J. 32, 88.

On Phosphorescence in General. Plac. Heinrich. Die Phosphorescenz der Körper. Abhandl. 1 bis 5.

Nürnberg. 1811, bis 20. Dessaignes, sur les Phosphorescences. J. Phys. 68, 444; 69, 5; 73, 41; 74, 101, and 173 (the later memoirs also in Schw, 8, 70, and 115).

On the Phosphorescence of Living Animals and Plants. Viviani. Phosphorescentia Maris. Genuæ. 1805. Spallanzani, on Phosphorescent Medusa; in his Reisen durch beide Sici

lien. Leipz. 4, 173. Treviranus, on Phosphorescent Appearances in Organic Nature; in his

Biologie, 5, 81. Macartney, on Luminous Animals, Schw. 10, 409; also Gilb. 61, 1, and

113; in the last, with observations by Tilesius. Tilesius. Investigations on the Luminosity of the Sea. Gilb. 61, 36. Grotthuss, on the Phosphorescence of Lampyris Italica. Ann. Chim. 64,

38; also N. Gehl. 5, 613. Macaire, on the Phosphorescence of Lampyres. Bibl. univ. 1821, May;

also Ann. Chim. Phys. 17, 151; also Gilb. 70, 265; abstr. Schw. 33,

254. Carus. Phosphorescence of the Lampyris; in the Analekte für Natur

wissenschaft u. Heilkunde. Dresden, 1829, p. 169.

Phosphorescence of the Sea: Wässtroem. Gilb. 2, 352.-Labillardière. Gilb. 30, 169.-Le Gentil. Samml. von Reisebeschreibungen. Hamburg, Th. 1.- Newland; Bajon, Condremière; Diquemare: in Rozier Observations, 2, 13; 3, 104; 5, 451; 6, 319.-Cook; Sparmann; Forster: in the Accounts of their Voyages.—Hellwig. Gilb. 50, 126.- Artaud. Ann. Maritim. et Colonial. 1825; 364; abstr. Schw. 52, 319.—Pfaff. Schw. 52, 316.—Bonnycastle. Schw. 61, 56. Percy, on the Phosphorescence of Wounds. Schw. 35, 228. Bischof, on the Phosphorescence of Rhizomorphs. Verhandl. der Leop. Carol. Akad. d. Naturf. 11, 603; also Schw. 39, 259. L. C. Treviranus. Whether are Light and Heat developed in the Vital

action of Plants? Tiedemann Zeitschr. f. Physiol. 3, 257. Zawadsky. Momentary Luminosity of flowers. Zeitschr. Ph. Math. 6, 459.

On the Phosphorescence of Dead Animals and Plants. Hulme, on the Light which streams out from certain Bodies. Gilb. 12,

129 and 292; the first half also in Scher. J. 8, 422. Büchner. Luminosity of Calves' flesh. Repert, 33, 422. D. Cooper and Appleton. Luminosity of Human Corpses. Phil. Mag.

J. 12, 420; also J. Chim. Med. 14, 505; also J. pr. Chem. 14, 173.

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