ANNALS OF PHILOSOPHY. JANUARY, 1815. ARTICLE I. Sketch of the latest Improvements in the Physical Sciences. AFTER an almost total exclusion from the Continent for about seven years, all the kingdoms of Europe have been suddenly thrown open; and it has been in our power, by importing the different foreign journals, to make ourselves acquainted with the various additions which the sciences have received during this eventful period. But these journals amount to so many volumes, that I find myself overwhelmed with matter, and foresee with regret that it will be utterly impossible for me to lay before my readers an historical sketch of the improvements which have been made in all the physical sciences. I shall therefore be under the necessity of confining myself, at least at present, to those scierces which have been cultivated with the greatest ardour, and in which the most important improvements have taken place. These are Chemistry and Mineralogy. I shall pass more slightly ove' what has been done in these sciences in Britain and France; because the journals and scientific works of these countries have already become in some measure known to my readers; partly by the contents of the Annals of Philosophy, and partly by means of the other London scientific journals. I shall dwell chiefly on what has been done in Germany and the North of Europe; because the languages of these countries are not much cultivated in Britair, and because our connection with them was so completely interrupted, that there is a considerable probability that most of the facs which I shall state are unknown to at least the greater number of my readers. Next to chemistry and mineralogy, electricity, magnetism, and VOL. V. N° I. optics, have been studied on the Continent with the greatest attention. I shall take a subsequent opportunity of laying the improve, ments made in these sciences before the reader. CHEMISTRY. This science embraces so vast a field, and is cultivated by so numerous a tribe of votaries, that its annual progress is exceedingly striking and rapid. I shall, for the sake of perspicuity, arrange the facts I have to state under different heads; because I consider any arrangement, even though imperfect, as greatly preferable to no arrangement at all. 1. General Principles. There are two general principles in chemistry of the utmost importance, which have lately attracted a great deal of the attention of chemists, and concerning which various theories have been started which have had considerable influence on the science. These two principles are, 1. The power by which bodies unite chemically. This power is usually known by the name of affinity. 2. The proportions in which bodies unite chemically. The facts established relative to this point have received the name of the atomic theory. I shall endeavour to lay a short view of the opinions relative to these two principles before my readers. I. Affinity.In the year 1803 an elaborate set of electrical experiments on the decomposition of salts and other bodics by the Galvanic pile was published by Hisinger and Berzelius. This paper was republished in 1806 by the authors in the Swedish language. † In 1803 an abstract of this paper was translated from the German, and published by the French chemists at Paris. Among other conclusions from their experiments, the authors draw the following: Substances are decomposed by electricity according to a determinate law. Oxygen and acids are attracted to the positive pole; while hydrogen, alkalies, earths, and metals, are attracted to the negative pole. This they consider as owing to an affinity subsisting between oxygen, and acids, and positive electricity; and between hydrogen, alkalies, earths and metals, and negative electricity. This important principle was still further developed by Sir Humphry Davy, and placed in a very luminous point of view in his celebrated lecture On sone Chemical Agencies of Electricity, published in the Transacions of the Royal Society for 1808, and which gained the prize proposed by Bonaparte for the most important discovery in galvanism. This dissertation deserves, in every point of view, to be considerd as the most valuable of all Sir Humphry Davy's philosophical iscoveries, His subsequent discoveries were more brilliant, and gave him greater eclat; but they were all derived from this probund dissertation, which pointed out the means of Gehlens neues allgemeines Journal der Chemie, i. 116. + Afhandingar i Fysik, Kemi och Mineralogi, i, I. Annales Chimie, li, 167. employing galvanism as an instrument of analysis, and the proba bility by means of it of decomposing many bodies which had previously resisted all the efforts of chemical experiment. In this dissertation the author showed that bodies which have a chemical affinity for each other are in different states of electricity; the one being negative, and the other positive. Thus when quicklime and oxalic acid are brought in contact, and separated, the acid is found to be negative, and the lime positive. Hence the reason why oxygen and acids are attracted by the negative pole of the battery. They are charged positively; and it is a law in clectricity that bodies in different states are attracted by each other. Hydrogen, alkalies, earths, and oxides, are in a positive state of excitement; therefore they are attracted to the negative pole of the battery. Sir H. Davy conceives, with Volta, that there is a peculiar state of electricity, either positive or negative, which belongs to every body; that bodies which have an athinity for each other are in different states, and that the degree of affinity is proportional to the intensity of these different states: or, in other words, the more positive one body is, and the more negative another, the greater is the affinity between them. If we bring them into the same state, that is, render them both positive or both negative, they will no longer remain in combination, but will separate from each other. Hence the reason why common electricity and the galvanic battery decomposes bodies; and it is probable that by its means most bodies may be decomposed, because the affinity between all bodies must be definite, whereas the galvanic intensity may be increased at pleasure almost to any amount. According to this view of the subject, chemical affinity is the same power with the attraction which exists between bodies in different states of electrical excitement; and if any means can be fallen upon to measure this power, we shall at the same time have a measure of chemical affinity. Such is an outline of the hypothesis of Sir Humphry Davy. Every one, I conceive, who has considered it with attention, must admit the great importance of it as a means of advancing our knowledge of the constituents of bodies, and be aware that it was in consequence of it that Sir H. Davy was led to attempt the decomposition of the alkalies and earths, and to obtain the splendid success with which these fortunate attempts were attended. He will recollect also the facts advanced in support of it by Volta and Mr. Brande, and the happy facility with which it enables us to explain many things that formerly appeared exceedingly obscure. I am far from pretending to call in question the probability that this hypothesis may ultimately turn out accurate, and think it entitled to the closest attention of every chemist and electrician; but if it be correct, I conceive that the theory of electricity, which at present prevails, will not be able to stand its ground. If negative and positive electricity be qualities inherent in bodies, and continuing in them after they unite together, I cannot for my part conceive the one to consist in a deficiency of electric matter, and the other in an excess of it. Neither can I conceive with M. Dufay, the Abbe Hauy, and some other French electricians, that negative electricity consists in one fluid, and positive electricity in another, which have an attraction for each other, and neutralize each other when they come in contact. But I can conceive negative and positive electricity to be two attractions inherent in different bodies, which make them unite with each other, and keep them united. But if we adopt this view of the subject, we are not only embarrassed by the difficulty of explaining many electrical phenomena, but we lose the benefit of all the facts stated by Volta, and of most of those advanced by Sir H. Davy in favour of his hypothesis. I myself, therefore, though disposed to think favourably of the Davian hypothesis of chemical affinity, consider it as very far from being sufficiently established to constitute the basis of our researches and our arrangements. This, however, has been done by Berzelius, who has bestowed much attention on it, and is certainly far better acquainted with the facts brought to light in support of it than I can pretend to be. His view of the subject does not differ much from that of Sir H. Davy; but the additions which he has made when we come to compare them with the present theory of electricity, or with any theory hitherto proposed, are sufficiently puzzling. According to him the acid or alkaline nature of a body depends upon the state of its electricity. If it be permanently negative, it is of an acid nature; if it be permanently positive, it is alkaline. But when he adds that a body may be positive with respect to one body, and negative with respect to another; though nothing is more easy than to reconcile this with the common doctrine of chemical affinity, it would be somewhat difficult to reconcile it with the theory of etectricity. I am far from saying that the thing is impossible; but in order to attempt an explanation of it with success, it would be necessary to make very sweeping changes in the electrical doctrines at present admitted. Berzelius has given a table of the chemical substances in the order of the intensity of their electricities, beginning with the one attracted most strongly to the positive pole, or the most intensely negative substance; and terminating with the body which is attracted most strongly to the negative pole, and therefore is most intensely positive. The negative intensity diminishes as we proceed downwards in the table, and at last in the centre finally disappears. Then the positive intensity begins; at first very weak, but it gradually increases as we go downwards, and becomes greatest at the lower end of the table. Hence the affinity of the two substances at the two extremes of the table is greatest of all; and as we advance to the middle of the table, that affinity gradually diminishes, and at last disappears. As I do not know the data from which Berzelius constructed his table, I have no means of judging of its accuracy; but I shall give the table in this place, as being well entitled to the attention of the chemical reader. It is doubtless susceptible of great improvements: but such a table, if it could be constructed with accuracy, would be of prodigious service to the progress of scientific chemistry. According to this table, oxygen and potassium have the greatest affinity for each other; and there is very little affinity between iridium, platinum, and gold. M. Oersted published at Berlin, in 1812, a work 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 he has not been so reserved as these philosophers. On the contrary, he has pushed matters as far as they will go, and has endeavoured to make his electrical hypothesis complete in all its parts. As this theory has attracted great attention, and gained great eclat in Germany, though I believe it is entirely unknown in Britain, I shall give the outlines of it in this place. He considers the phenomena of electricity, galvanism, magnetism, heat, light, and chemical affinity, as all depending on the same forces; and he shows that the same cause, which in one case produces electrical actions, occasions in another chemical actions. These actions are produced by two forces; the one negative, the other positive. These forces are opposite to one another; and by being made to act against one another, may suspend or destroy one another. Heat is produced by the extinction of the two forces, either in electrical or chemical processes. We may suppose also that the light is derived from the same cause. Acids 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. Oersted arranges chemical substances under two series: the first containing the products of combustion; the second, the |