supporters and combustibles. Those of the one series, according to him, do not combine with those of the other; except sulphur and phosphorus, which combine both with the metals and alkalies, and therefore constitute, as it were, the transition from the one series to the other, 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 continuing to the least combustible, as platinum, rhodium, iridium. If we suppose the series continued farther, we are led to the idea of a body absolutely incombustible. This body must possess in the highest degree the properties which are the opposite to combustibility, and in consequence of the attraction which exists between it and combustible bodies, it must produce the strongest action, which is that of combustion. This incombustible body, in the present state of our knowledge, is oxygen.

Between oxygen and iridium the author places carbon, phosphorus, and sulphur. This last substance, though heat makes it pass into the state of a combustible, ought to be considered as a negative body.

The products constitute a similar series, which commences with the most energetic alkalies, and passes to those which are more feeble, till we come to bodies such as alumina, in which that property is balanced by the opposite property having the same force. Then come bodies of a predominating acidity. This is at first feeble in the bodies nearest the point of equilibrium, but it becomes of an extreme activity in the bodies at the greatest distance from that point. We see that each series commences with a certain sum of a property, which diminishes in arithmetical progression, and terminates by leaving the bodies possessed of the opposite property.

Two bodies which belong to the opposite extremes of a series combine with great force; but the energy of this action seems to change their state, since the product of the combination no longer belongs to the same order of affinities. The compounds of oxygen and a combustible body pass into the series of products, as likewise do those of hydrogen and sulphur, of tellurium, and without doubt those of various other bodies. The compound of an acid and alkali no longer belongs to the series of products, but to that of the salts. On the other hand, compounds between bodies at no great distance from each other, as between two acids or two alkalies, do not go out of the series.

This law embraces all the bodies having the same preponderating forces; so, however, that these bodies cannot be confounded. It presents, says the author, under a simple expression this truth, that the same force may exist in a state so different that all its attraction for the opposite force will not be sufficient to make it enter into combination. The two most different states are found in the supporters and the products. The third state is in the neutral salts; but they bear a close resemblance to those products that are placed near the point of equilibrium. Combustibility, then, is the pre

ponderance of the positive force in a particular state, which M. Oersted calls the state of supporters, or of the first class of bodies. Alkalinity presents the same force, but in a different state, which he calls the state of products, or of the second class. We do not know the nature of this difference, but we know that it exists, and that the forces are in a state of greater liberty in the first class than in the second.

Combustion sometimes gives us alkaline products, sometimes acid, and sometimes neutral ones. The 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. If the body be combustible in a high degree, and does not combine with too much oxygen, the positive force still preserves the preponderance, and the body is alkaline. If, on the contrary, the body be but little combustible, and combine with a great deal of oxygen, the negative force remains preponderant, and the body is acid.

In oxygenated bodies we find of necessity a combustible body and oxygen united together, and constituting a body of the second class. Hence we must conclude that these bodies unite together the two opposite properties, the alkaline and acid, one of which is often. rendered insensible by the other. However, in a great number of other combinations, both properties subsist together. This is the case in the oxides of lead, copper, &c. In some bodies we find the positive or negative force in both states at the same time. Thus ammonia possesses both the positive force of the first class and that of the second; while the nitric and oxymuriatic acids possess the negative force both of the first and second class. This is the natural effect of a combination, either feeble or far from the point of saturation, by which a force is reduced to an inferior state. In the combination of tellurium with hydrogen, the negative force of the metal is sufficiently changed by the positive force of the hydrogen to occasion a state of acidity. The positive force contained either in the hydrogen or in the tellurium has not suffered enough of change to come to the state of acid. Hence we find in tellureted hydrogen gas a strong combustibility, and a very distinct acidity, existing together.

It is well known that electricity produces heat. M. Oersted ascribes this effect to a union between the two opposite electric forces; and it is so much the more intense, the greater obstacles the transmission of the electricity meets with, provided that these obstacles may be overcome. The transmission of electricity consists in a series of attractions and repulsions, or in the undulatory movement experienced by the peculiar forces of the body. Chemical union between electro-negative and electro-positive bodies excites always heat, and none of the electrical forces escapes in a state of liberty. However, the increase of conducting power may counterbalance this effect, and even overcome it, and then cold is excited. There exists three principal combinations between the electrical

forces, which are the same as the chemical forces. The first is the combination between the forces themselves; the result of it is the contraction of the two forces, or their reduction to a smaller volume, with the disengagement of light and heat. The second is the combination of a product with a supporter. The result of it likewise is condensation, and the evolution of light and heat, though not to so great an extent as in the first case. The third degree consists in the combination of an alkali with an acid. It is rarely accompanied by the disengagement of light, but always with the disengagement of heat. A condensation likewise takes place unless peculiar causes modify the result. Expansion, which is the effect of a repulsive force in bodies, is most frequently owing to an excess of one of the electric forces. Contraction is the effect of an equilibrium between the forces, and of their mutual extinction. The forces which produce the electrical and chemical actions of bodies are the same as those which produce the mechanical properties of bodies. Impenetrability 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 one another. Universal attraction consists in the action at a distance of the two forces upon each other, supposing the expansive power of each force not to extend beyond the surface of bodies.

Such is an abstract of M. Oersted's hypothesis, as far as I have been able to make it out. It is fair, however, to state, that I have not had an opportunity of perusing his own work, but only the abstracts of it published in some of the German journals, and an outline given by Van Mons in his translation of Sir H. Davy's Elementary Work. Hence it is very possible that I may not have done the author justice, and that some of the parts of his hypothesis, which appear the most whimsical and absurd, would assume another aspect under the explanations of the author himself. On that account I shall not attempt any critical examination of this hypothesis, which has given the author considerable celebrity in Germany. Its weak parts and inconsistencies are sufficiently obvious to those who have followed the late improvements in electricity and chemistry. The metaphysical part I do not fully understand; nor have I been able to make out whether the author's electrical forces be substances or qualities.

At present, then, it seems to be the prevailing opinion of chemists that chemical affinity is identical with electrical attraction. The opinion possesses much plausibility, and even probability; but much remains to be done before it can be considered as established, and made the foundation of our chemical reasonings.

II. Proportions in which Bodies combine chemically.-That the ultimate particles of matter consist of atoms, incapable of farther subdivision, is an opinion which has been pretty generally received among philosophers ever since the time of the Greeks; and since the establishment of the Newtonian philosophy this opinion has

become almost universal. That substances àlways enter into chemical combination, in determinate proportions which never vary, has been known ever since chemists acquired the art of analysing bodies. Thus carbonate of lime, wherever, or in whatever state, it occurs, is always a compound of 43.2 carbonic acid and 57.8 lime; and sulphate of barytes, of 34.5 sulphuric acid and 65.5 barytes. In like manner, the yellow oxide of lead is always a compound of 100 lead and 7-7 oxygen; and red oxide of mercury, of 100 mercury and 8 oxygen. Sulphuric acid is always composed of three parts of oxygen and two parts of sulphur; and carbonic acid, of 2000 oxygen and 751 carbon. This law is universally admitted by chemists; and, indeed, the more rigorously it has been examined, the more conspicuous and decided have become the proofs in its favour. Even Berthollet, who seems to be an enemy to the atomic theory in the abstract, has admitted that all known compounds unite in determinate proportions; and has endeavoured to reconcile this fact to his own opinions by several highly ingenious, and some rather whimsical, arguments. The few exceptions which he was able to muster up against the law have all disappeared before the more rigid and exact examination of modern analysts.

Mr. Dalton was the first person who ventured to account for this fixedness in chemical proportions. According to him, it is the atoms of bodies that unite together. One atom of a body, a, unites with one atom of a body, b, or with two atoms of it, or with three, four, &c. atoms of it. The union of one atom of a with one atom of produces one compound, the union of one atom of a with two atoms of produces another compound, and so on. Each of these compounds, of course, must consist of the same proportions, be cause the weight of every atom of the same body must of necessity be the same.

We have no means of demonstrating the number of atoms which unite together in this manner in every compound; we must, therefore, have recourse to conjecture. If two bodies unite only in one proportion, it is reasonable to conclude that they unite atom to atom. Hence it is most likely that water is composed of one atom of oxygen and one atom of hydrogen; oxide of silver, of one atom silver and one atom oxygen; and oxide of zinc, of one atom zinc and one atom oxygen.

When a body has the property of uniting with various doses of oxygen, we can then determine the number of atoms which constitute the compounds. Thus manganese unites with four doses of oxygen; and supposing the manganese to be represented by 100, the oxygen of each respective oxide is represented by the numbers 14, 28, 42, 56; but these numbers are to each other as the numbers one, two, three, four. Hence the first oxide is composed of one atom manganese and one atom oxygen; the second, of one atom manganese and two atoms oxygen; the third, of one atom manganese and three atoms oxygen; and the fourth, of one atom manganese and four atoms oxygen. In like manner, as mercury

combines with two doses of oxygen, and forms two oxides, the first composed of 100 mercury and four oxygen, and the second of 100 mercury and eight oxygen, it is obvious that the first must be a compound of one atom mercury and one atom oxygen, and the second of one atom mercury and two atoms oxygen.

Nor is there any difficulty with respect to iron. There are two oxides of that metal: the first composed of 100 iron and 28 oxygen; the second of 100 iron and 42 oxygen. Now as 28 is to 42 as two to three, it follows that the first is a compound of one atom iron and two atoms oxygen; the second, of one atom iron and three atoms oxygen. The same rule holds good with respect to the oxides of nickel and cobalt.

If we know the number of atoms of which a body is combined, and the proportion of the constituents, there is no difficulty in determining the proportional weight of the atoms of which it is composed. Thus if water be composed of one atom of oxygen and one atom of hydrogen, and if the weight of the oxygen in water is to that of the hydrogen as 7+ to one, then it follows that the weight of an atom of oxygen is to that of an atom of hydrogen as 71⁄2 to one. If black oxide of mercury be composed of one atom of mercury and one atom of oxygen, and if it be composed of 100 mercury and four oxygen, then an atom of mercury is to the weight of an atom of oxygen as 100 to four, or as 25 to one. If black oxide of iron be composed of one atom iron and two atoms oxygen, and if it consist of 100 iron and 28 oxygen, then an atom of iron is to an atom of oxygen as 100 to 14, or as 7-142 to one. Such is the method of determining the weight of an atom of the different substances upon which experiment has hitherto been made. The advantage of such a knowledge is immense; because it gives us the proportions in which the different substances unite together, and even enables us to calculate the proportional constituents of all compound bodies, independent of experiment, and with more accuracy than would result from experiments unless conducted with uncommon precautions.

Hitherto the only persons who have written upon the subject of chemical atoms are Mr. Dalton, Sir Humphry Davy, Dr. Berzelius, Dr. Wollaston, and myself. Mr. Dalton made choice of hydrogen as his unit, because it is the lightest of all the atoms; and Sir H. Davy has followed his example. But as oxygen enters into a much greater number of compounds than any other body, it was chosen by Dr. Wollaston and Dr. Berzelius as the most convenient unit; and in the tables of atoms which I have published in the different volumes of the Annals of Philosophy, I have followed their example. Berzelius considers an atom of oxygen to weigh 100, Wollaston makes it weigh 10, and I myself make its weight one. The reader will perceive that these three numbers are the same, the only difference being the position of the decimal point.

The person who has hitherto made the greatest number of experiments upon this important subject is Dr. Berzelius; and he has