considerable weight to the conclusions which have been thus legitimately formed.

But of all the supporters of Sir Humphry's doctrine, Berzelius is, perhaps, the most active and decided. According to this distinguished chemist, not only the affinity of bodies, but also their acid or alkaline nature depends upon the state of their electricity. If it be permanently negative, it is acid; if permanently positive, it is alkaline. Here, however, difficulties start up; and when he adds, that the same body may be positive with regard to one, and negative with regard to another body, he certainly does the utmost violence to the commonly received notions on electricity.

M. Oersted of Berlin, published some time ago, a work which he entitled, "Considerations on the Physical laws of Chemistry deduced from the new Phenomena." Like Davy and Berzelius he has adopted the electrical theory of affinity; but instead of imitating the cautious reserve of these philosophers, he has stretched their principles as far as they would go, and endeavoured to make his electrical hypothesis complete in all its parts. We give an abridged view of his leading doctrines, agreeably to the conception formed of them by Dr. Thomson in his Annals of Philosophy; not having had access to the work itself, and being rather unwilling to waste time in reading it.

Oersted considers the phenomena of electricity, galvanism, magnetism, light, heat, and chemical affinity, as all depending on the same forces; and he attempts to show, that the same cause which, in one case, produces electrical action, produces chemical action in another. These actions are produced by two forces; the one negative, the other positive: which forces, again, are opposite to each other, and by being made to act against each other, may mutually suspend or destroy one another. Heat is produced by the extinction of the two forces either in electrical or chemical processes; and we are given to understand that light is derived from the same cause.

Acids, he further teaches, which are attracted to the same pole as oxygen, possess the same force with that principle; while alkalies and combustible bodies which are attracted to the opposite pole, possess the opposite force. It should be mentioned too, that he arranges chemical substances under two series; the first, containing the products of combustion, the second, supporters of combustion and combustibles. He endeavours to distribute the bodies in these series, in a kind of arithmetical progression, beginning with the most combustible bodies, as hydrogen, ammonia, potassium, and going on to the least combustible, as platinum, thodium, iridium, and arriving at last at

a body

a body completely incombustible, which body, in the present state of our knowledge, is oxygen.

The products of combustion constitute a similar series, commencing at the most energetic alkalies, and passing to those which are more feeble, till we come to such bodies as have the alkaline property balanced by a countervailing acidity. Thus, each series is found to begin with a certain amount of its peculiar property, which diminishes in arithmetical progression, and terminates by leaving the bodies possessed of the opposite property.

Combustion sometimes gives us alkaline products, sometimes acid, and sometimes neutral ones. The alkaline product, by combining with oxygen, loses, either in part or entirely, its free positive force, and passes to the order of bodies of the second state. The same thing happens to the negative force of the oxygen.

M. Oersted ascribes the phenomenon of heat to an union between the two opposite electric forces; and the effect is so much the greater, that is, the heat is so much more intense, the greater the obstacles are which the electricity encounters, provided these obstacles may be overcome.

According to the same author, there are certain principal combinations between the electrical forces which are the same as the chemical forces. The first is the combination of these forces themselves; of which the result is the contraction or reduction of their volume with the disengagement of light and heat. The second is the combination of a product with a supporter; resulting likewise in condensation with the evolution of light and heat. The third principal combination is that of an acid with an alkali; and this is always accompanied with the disengagement of heat, but rarely with that of light.

We have only to add, that Oersted regards the forces which produce electrical and chemical action, as being the same as those by which the mechanical properties of bodies are produced. Impenetrability, for example, depends on the resistance which the expansive power of two forces opposes to a body endeavouring to penetrate the space already occupied by another. body. Cohesion is the effect of the two forces, which attract each other. Universal attraction consists in the reciprocal action, at a distance, of the two forces, supposing the expansive power of each force not to extend beyond the surface of bodies*.

*See Thomson's Annals, for January, 1815.

It must have struck the reader, that the simplicity of Sir Humphry's views is completely lost sight of, in the chemical metaphysics which we have just detailed; and we seriously apprehend, that the zeal of this Prussian ally will prove more hurtful to the cause which he has chosen to espouse, than if he had summoned all the science and logic of his nation, to oppugu it by argument. The doctrine, however, seems to gain ground which holds the identity of chemical affinity and electrical attraction; and illustrated as it has been by the brilliant discoveries of Davy, it cannot fail to secure the attention of every philosophical chemist.

What has been said relates to the power or energy which impels bodies to enter into chemical union: we have next to consider the new doctrines relative to the proportions in which substances combine chemically.

The opinions hitherto best known on this subject are those of Berthollet. This ingenious and profound writer maintains, that it is the tendency of chemical attraction to combine bodies with-out any limits as to proportion; and that such limits, where they do present themselves, arise not from the nature of the thing itself, but from those external circumstances by which the exer tion of the power in question is always modified. These circumstances are cohesion, elasticity, fluidity and others. Independently of these Berthollet asserts that bodies would unite in proportions absolutely indefinite, and that chemical attraction, in all cases, operates in a ratio made up of the affinity and the relative quantity of matter in the masses brought into contact.

An opinion diametrically opposite to this has been maintained by the most distinguished of modern chemists, Davy, Berzelius, Wollaston, Thomson and Dalton, namely, that substances unite in proportions which are rendered definite by the sole ope ration of their mutual affinity, and that all compounds of the same bodies are equally defined, as to the number or weight of their constituent particles. These particles are denominated atoms, whence has been derived the title of the Atomic theory; and in relation to the leading doctrine on which it rests, it is also denominated the theory of definite proportions.

It has been long known that certain substances enter into chemical union, in determinate proportions which never vary. Thus the common mineral called carbonate of lime is uniformly found to consist of 43.2 carbonic acid, and 57.8 lime. Sulphuric acid is always composed of three parts of oxygen and two parts of sulphur: and carbonic acid, of 2000 oxygen and 751 carbon. Several attempts at generalization had been made by foreign chemists, but it was reserved for our countryman Mr. Dalton to explain these interesting facts by referring them to a determinate

determinate law. After a most extensive and laborious induction of particulars, Mr. D. arrived at the following conclusion, which may be regarded as the rule or principle for chemical combination. When two bodies combine in different proportions, if the quantity of one of them be assumed as a fixed number, the proportions of the other uniting to it, are in the simplest possible ratio to each other, being produced by multiplying the lowest proportion by a simple integral number, as 2, 3, 4, &c. We shall now quote a few illustrations of this rule from Dr. Aikin's supplement.

"If a metal can combine chemically with different proportions of oxygen, if 100 of the metal take 9 of oxygen for the lowest degree of oxygenation, all the other degrees will be in the proportion of 100 of metal to twice 9 (18) of oxygen, or 100 of metal to three times 9 (27) of oxygen, or 100 of metal to four times 9 (36) of oxygen, &c. &c. A reason for this simplicity in the ratio of binary compounds, may be found in the general principle assumed by Mr. Dalton, which is, that in all cases, the simple elements of bodies are disposed to unite atom to atom singly, or, if either is in excess, it exceeds by a ratio, to be expressed by some simple multiple of the number of its atoms.

"Hence, from the relative weights of the constituent parts of a compound, Mr. Dalton infers the relative weights of the ultimate particles or atoms of each of these parts; and, this being found, the number of atoms of each constituent which enters into the formation of the compound particle is also deduced.

"Thus (taking a compound of two constituent parts A and B, as the simplest case,) if its elements are found by experiment to unite in the proportion of 5 of A to 7 of B, it is inferred by Mr. Dalton, that the numbers 5 and 7 express the comparative weight of an atom of A and B respectively. And these elements, though uniting in several proportions, will yet be found by experiment to be confined to either 5 A to 14, 21, 28, &c. of B, which is one atom of A to 2, 3, 4, &c. atoms of B; or, conversely, it will be 7 B to 10, 15, 20, &c. of A, which is one atom of B, to 2, 3, 4, &c. atoms of A. It is essential to the consistency of this system, therefore, that there should be no other proportions of combination between these two elements, unless indeed it be one that is expressed by an even sub-division of one of these proportions, as, for example, 5 of A, to 7, 101, 14, &c. of B; in which case, the 10 being resolvable into three portions of 3 each, the num ber expressing the relative weight of an atom of B, must be reduced to 3 instead of 7, and consequently the several proportions of 7, 10, 14, and 21 of B, will be resolved respectively, into 2, 3, 4, and 6 atoms of B."

When a compound consists of two elements in which one atom of each is combined, the double atom is called binary.

The

The epithet ternary, is given to an atom which is composed of two elements, in the proportion of two atoms of the one element to one atom of the other: and when an atom is composed of three atoms of one element with one atom of the other, it is denominated quaternary. We shall subjom a few facts abridged from Aikin's appendix, for the sake of illustrating more fully the chemical union of substances in definite proportions.

"If one measure of pure oxygen, and two measures of hydrogen, be mixed in a jar over mercury, and ignited by the electric spark, both the gases will disappear, and water will be produced. If two measures of each gas be used, water will be produced as before, but one measure of oxygen will remain. Hydrogen, therefore, in the composition of water, unites with oxygen in one exact proportion and no other.

"If a piece of well-burnt charcoal be confined in oxygen gas, and inflamed by a burning-glass, the volume of gas is not altered when again cooled, but the whole is converted into carbonic-acidgas. If more oxygen be present than is necessary for the consumption of the charcoal, the product will be carbonic-acid-gas and an excess of oxygen; if there is less oxygen than will consume the charcoal, carbonic acid alone will be produced, and part of the charcoal will remain unconsumed.

"The combination of two elements, in several definite propor tions, is very happily shown by the various compounds of hydrogen and azote. These are nitrous oxyde, nitrous gas, and nitrous-acid

gas.

"If two measures of nitrous oxyde and two measures of hydrogen are ignited by the electric spark, the product is water, and two measures of azote remain. Now, as water is produced by two measures of hydrogen and one of oxygen, the nitrous oxyde here employed must have consisted of two measures of azote with one of oxygen, condensed into the space of one measure.

"If charcoal is ignited in two measures of nitrous gas, the products are one measure of carbonic-acid-gas, and one measure of azote. Hence, as carbonic-acid-gas always occupies the same volume as the oxygen of which it is formed, nitrous gas consists of equal volumes of oxygen and of azote, not condensed by their union.

"If two measures of nitrous gas be mixed over water, with one measure of oxygen gas, both of them totally disappear, and a solution of nitrous-acid-gas in water is the result."

We cannot enter into the detail of Berzelius's numerous experiments, which were instituted, with the express view, of illustrating the important doctrine of definite proportions. We confine ourselves to one example, namely, the combination of lead and oxygen. Lead, it is well known, admits three degrees

of