gold-atom possesses. Suppose for instance that the quantity of negative electricity at one pole of the gold-atom = 1, of the positive electricity at the other = 2, of the negative at one pole of the sulphur-atom = 12, and that of the positive at the other pole 4; then the positive electricity will predominate in the gold-atom and the negative in the sulphur, but the sulphur will possess a much higher degree of electrical polarization than the gold; the positive electricity accumulated at its positive pole will therefore be able to neutralize a greater quantity of negative electricity in the oxygen than the positive electricity of the gold; hence the greater tendency of oxygen to combine with sulphur than with gold.

In the same body, the degree of electrical polarisation,-i. e. the absolute quantity of the two electricities in the atomic poles-varies, according to Berzelius, with the temperature, and is generally increased by elevation of temperature. Many bodies, such as carbon, which appear to have but very weak polarisation at common temperatures, often become highly polarized at a red heat,—hence their combination with oxygen at that temperature. Many substances, on the contrary, such as gold, which have altogether but weak polarization, frequently show it in a greater degree at low than at high temperatures, at which indeed it often disappears entirely.

Electro-negative bodies in combination with oxygen generally form electro-negative compounds; e. g. sulphur produces sulphuric acid; electro-positive substances give electro-positive compounds; e. g. potassium produces potash.

The decomposition of a compound produced by electro-chemical neutralization can only take place when the elements have their former polarity restored to them. That the united elements, after the neutralization of their opposite electrical states, are held together by a force which resists all mechanical means of separation, does not result from any innate power (affinity); otherwise the permanence of the combination would not be subject to the influence of electricity. But the most intimate chemical combination may be destroyed by restoring the electrical polarity of the elements. In this decomposition of compounds by the electrical current, the acting electricities disappear and the elements reassume their former chemical and electrical properties. If A B is resolved by C into A C and B, C must have greater intensity of electrical polarization than B. Hence there results more complete neutralization between A and C than that which before existed between A and B; this gives rise to development of heat, and B reappears with its original polarity. A substance capable of combining with others, sometimes as an electro-positive sometimes as an electro-negative element, can only be separated from the first mentioned combinations by bodies still more positive, and from the latter by bodies still more negative: e. g. sulphur can only be separated from its combinations with oxygen by bodies which are more positive, and from its combination with lead by bodies which are more negative than itself.

This theory of Berzelius is encumbered with the following difficulties: (1). No precise demarcation can be drawn between the less intimate chemical combinations supposed to be produced by affinity and the more intimate ones which are ascribed to electrical action. At all events it does not seem conformable to nature to assume the existence of two totally different causes for these two very similar classes of compounds. According to this view, one atom of sulphuric acid should combine with the first two or three atoms of water, not by affinity but by electrical attraction,

and with any further quantity of water by affinity. Now if sulphuric acid combined with three atoms of water, possess affinity for water, why should not the same acid when pure or when combined with one atom of water, also have affinity for water?-(2). What is it that induces the two electricities to accumulate each by itself in definite quantity, on two opposite points of an atom which must be regarded as a homogeneous mass? What prevents their combination? Are the atoms of all bodies, even of metals, perfect non-conductors? Again, when sulphur and lead are melted together, the negative electricity of the sulphur-atoms is sup posed by Berzelius to combine with the positive electricity of the leadatoms, the combination being accompanied by a development of light and heat. Why does not the negative electricity at one pole of an atom of sulphur combine with the positive electricity at the opposite pole of another atom and produce fire, when the sulphur is melted by itself?— (3). If combinations are produced not by the affinity of the elements but by electrical polarity, every substance, simple or compound, should be capable of combining with every other whose atomic poles contain the two electricities in different proportions; why, for example, should the predominating positive electricity of mercury combine with the negative electricity of tellurium and not with that of carbon?-(4). It is not easy to discover by what force combined substances are held together. The heterogeneous atoms unite in consequence of their adhesion to the opposite electricities; but when these have been neutralized by combination, it might be expected that the atoms would fall asunder and allow themselves to be easily separated by friction and other mechanical forces, which is by no means the case. In order to overcome this difficulty, Dumas supposes (Philos. of Chem.) that in the combination of oxygen and hydrogen, for example, the negative pole of the former places itself towards the positive pole of the latter, and the positive pole of the former towards the negative pole of the latter; moreover, that the atoms can only give up the electricity of one of their poles-that it is only on this side that electrical neutralization takes place, viz., of the negative electricity of the oxygen with the positive of the hydrogen-that on the contrary the electricities of the two other poles, viz., the positive of the oxygen and the negative of the hydrogen remain uncombined, and hold the atoms united by their mutual attraction. But this assumption-that the electricity of only one pole of an atom can combine with the opposite electricity of another, and that those of the other poles are incapable of uniting-would not only be a new enigma, but admits of positive contradiction; for in the combination of sulphur with oxygen, the positive electricity of the sulphur must unite with the negative of the oxygen; and in the combination of sulphur with the metals, its negative electricity with the positive of the metal. Einbrodt's explanation (Ann. Chim. Phys. 61, 262; also J. pr. Chem. 8, 345,) agrees in the main with that of Dumas.

The theory adopted in the present work is as follows:-Ponderable bodies have affinity for one another. The two electricities are substances which likewise possess affinity for each other, and by whose combination in the proportions in which they neutralize each other, heat (fire) is produced. The individual electricities, and likewise heat, have considerable affinity for ponderable substances, and are united to them with greater force and in greater quantity, the more simple these ponderable substances are. Ponderable bodies, according to their nature, have a greater or less excess of positive or negative electricity united with them in addition to a definite quantity of heat. Thus, oxygen probably contains the greatest

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. g., 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 potassium 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 Hypothesis.

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, Ideen zu einer Philosophie der Natur. Aufl. 2, 1803, s. 453.)

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

PART II.

SPECIAL CHEMISTRY,

OR

THEORY OF THE AFFINITY OF INDIVIDUAL SUBSTANCES.

SECTION I.

CHEMISTRY OF IMPONDERABLE Bodies.

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.