Mr. Humphry Davy, Lecturer on Chemistry in the Royal Institution; communicated by Benjamin, count of Rumford, V.P.R.S." In order to appreciate the value of this paper, it must be remembered, that the agencies of two metals in exciting galvanic phenomena were at that time supposed to be directly connected with the different powers of such metals to conduct electricity. Davy was the first philosopher who corrected this error, and, in the paper before us, showed that the evolution of galvanic energy was connected with chemical action; an inference which he de-, duced from some experiments, by which he found that an accumulation of galvanic influence (exactly similar to that in the common pile where two metals are used) might be produced by the arrangement of single metals, with different strata of fluids. This theory he established by a great variety of experiments, and showed that the alternation of two metals with fluids was no further necessary to the production of accumulated galvanic influence, than as it furnished two conducting surfaces of different degrees of oxidability; and that this production would take place, if single metallic plates were connected together by different fluids, in such a manner that one of their surfaces only should undergo oxidation, the arrangement being regular. He moreover ascertained that many of these arrangements could be made active not only when oxidation, but likewise when other chemical changes were going on in some of their parts. Here, then, appeared the dawn of the electro-chemical theory. The main fact stated in

Davy's paper, namely, the relation between the energy of the pile and the oxidation of one of its metals by the interposed fluid, was readily admitted; but a question arose, whether the oxidation, instead of being the primary cause, might not be the effect of the electricity, set in motion by the contact of metals, endowed with different conducting powers. Upon this occasion, with an alacrity corresponding with the importance of the subject, Dr. Wollaston appeared in the arena, and at the meeting succeeding that at which Davy's paper was read, related to the society a series of experiments, which fully confirmed the views of Davy, and set the question for ever at rest. This fact illustrates some of the most prominent features in the scientific character of Wollaston-the quickness of his perception, the solidity of his judgment, and, above all, the liberality and candour with which he lent his powerful aid for the promotion and advantage of a rival philosopher.

An interval of nearly five years now elapsed before Davy threw any further light upon this branch of science; but his energies had not slumbered; he had been engaged in experiments of the most arduous and complicated description; and in presenting their results, he unfolded the mysteries of Voltaic action, and, as far as its theory goes, might almost be said to have perfected our knowledge of the galvanic pile. The memoir in which these discoveries were announced constituted the Bakerian lecture; and was read before the Royal Society on the 20th November, 1806. It had been observed, during some of

the earliest chemical experiments with the Voltaic pile, that when the purest water was submitted to the action of a current of electricity, acid and alkaline matter was separated at the opposite electrified surfaces. A fact so extraordinary necessarily excited various conjectures; and many believed that the bodies were actually generated by the action of the pile. Davy, however, soon negatived so unphilosophical a conclusion, and showed that they merely arose from the decomposition of the materials employed: he found, for instance, that the glass vessel, at its point of contact with the wire, was corroded; a fact which sufficiently explained the source of the alkali; while the animal or vegetable materials, employed as conductors, might be readily supposed to furnish the acid. He accordingly proceeded to work with cups of agate; and, at the suggestion of Dr. Wollaston, who again acted as a Mentor, he formed the connecting parts of wellwashed asbestos. Thus then was every source of fallacy connected with the apparatus removed; but still the same production of saline matter appeared. What could be its origin? He repeated the experiments in cups of gold, and examined the purity of his water by evaporation in vessels of silver. At length he succeeded in recognising the source of this matter: it was of foreign origin, partly derived from the contents of the water, and partly from new combinations of gaseous matter. This was curious, but, after all, a discovery in itself of insignificant value, when compared with those which immediately flowed from it. The acid and alkaline matter then

produced, it has been already stated, collected in the water round opposite poles; the former always appearing at the positively electrified, the latter at the negatively electrified, surface. Was this a universal law? It was necessary to decide this question by more extended inquiries. The first series of experiments which he instituted for this purpose, embraced the decomposition of solid bodies, insoluble, or difficultly soluble in water. From the effects of the electrical agency on glass, already mentioned, he very reasonably expected that various earthy compounds might thus undergo changes under similar circumstances; and his conclusion was just. From sulphate of lime he obtained sulphuric acid in the positive, and a solution of lime in the negative cup. These experiments were extended to a great variety of other compounds, such as sulphate of strontia, fluate of lime, sulphate of baryta, &c. and with parallel results. Having thus far established the general law, he proceeded to inquire into the mode and circumstances under which these constituent parts were transferred to their respective poles; and he discovered, first, that acid and alkaline bodies, during the time of their electrical transfer, would pass through water containing vegetable colours, without affecting them or combining with them; and, secondly, that such bodies would even pass through chemical menstrua having stronger attractions for them, thereby showing that the same power which destroyed elective affinity in the vicinity of the metallic points, would likewise destroy or suspend its operation,

throughout the whole of its circuit. In 1807, this Bakerian lecture, in despite of national prejudice and national vanity, was crowned by the Institute of France with the prize of Napoleon.

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The discovery of the position of the fixed alkalies, was announced in Davy's second Bakerian lecture, read before the Royal Society in 1807, and was the direct result of an application of the laws of Voltaic decomposition, developed in his lecture of the preceding year. Davy submitted a fixed alkali to the most intense action of the galvanic pile, believing that if it contained any hydrogen, or other inflammable basis, it would be separated at its negative extremity, and if any oxygen, that it would appear at the opposite end. His first attempts were made on solutions of the alkalies; but, notwithstanding the intensity of the electric action, the water alone was decomposed, oxygen and hydrogen being disengaged with violent effervescence, and transferred to their respective poles. The presence of water thus appearing to prevent the desired de composition, potass, in a state of igneous fusion, was submitted to experiment; when it was immediately evident that combustible matter of some kind, burning with a vivid light, was given off at the negative wire. After various trials, during the progress of which the numerous difficulties which successively arose were as immediately combated by ingenious manipulation, a small piece of potass, sufficiently moistened by the breath to impart to it a conducting power, was placed on an insulated disc of platina, and con

nected with the negative side of the battery in a state of intense activity, and a platina wire, communicating with the positive side, was at the same instant brought into contact with the upper surface of the alkali. What followed?-A series of phænomena, in strict accordance with those laws which Davy had previously discovered The potass began to fuse at both its points of electrization; a violent effervescence commenced at the upper or positive surface, while at the lower or negative, instead of any liberation of elastic matter, which must have happened had hydrogen been present, small globules, having the appearance of quicksilver, were disengaged, some of which were no sooner formed than they burnt with explosion and bright flame.

The gaseous matter developed at the positive pole, was soon identified as oxygen; but to collect the metallic matter at the opposite extremity, in a sufficient quantity for a satisfactory examination, was not so easy; for such was its attraction for oxygen, that it speedily reverted to the state of alkali by re-combining with it. After various trials, Davy found that recently-distilled naphtha presented a medium in which it might be preserved, by covering the metal with a thin transparent film of fluid, which defended it from the action of the air, and at the same time allowed an accurate examination of its physical qualities. Thus provided, he proceeded to investigate the properties of the body; giving to it the name of potassium. It is a white metal, instantly tarnishing by exposure to air; at the temperature of 70° Fahrenheit, it exists in

small globules, which possess the metallic lustre, opacity, and general appearance of mercury; so that when a globule of mercury is placed near one of potassium, the eye cannot discover any difference between them. At this temperature, however, the metal is only imperfectly fluid; but when gradually heated, it becomes more and more fluid; and at 150°, its fluidity is so perfect, that several globules may easily be made to run into one. By reducing its temperature, it becomes at 50° a soft and malleable solid, which has the lustre of polished silver; it is soft enough, indeed, to be moulded like wax. At about the freezing point of water, it becomes hard and brittle, and exhibits, when broken, a crystallized texture of perfect whiteness and high metallic splendour. It is also a perfect conductor of both electricity and heat. But instead of possessing the ponderosity usual in metallic bodies, it is so light as to swim not only upon the surface of water, but upon that of naphtha, by far the lightest fluid in nature. Thrown upon water, it instantly decomposes the fluid, and an explosion is produced with a vehement flame: an experiment which is rendered more striking if, for water, ice be substituted. In this latter case it instantly burns with a bright flame, and a deep hole is made in the ice, filled with a fluid, which is found to be a solution of potass. It is scarcely necessary to state that this phænomenon depends upon the very powerful affinity which the metal

possesses for oxygen, enabling it even to separate it from its most subtle combinations. The evidence afforded of the nature of the fixed

alkali, potass, is thus rendered complete. It is a metallic oxide, or, in other words, a body composed of oxygen, and a metal of the most singular description, so light as to swim upon water, and so inflammable as to catch fire by contact with ice!

The decomposition of the fixed alkali placed in the hands of the experimentalist a new instrument of analysis, scarcely less energetic, or of less universal application, than the power from which the discovery emanated. So strong is the affinity of potassium for oxygen, that it discovers and decomposes the small quantities of water contained in alcohol and ether. But, perhaps, the most beautiful illustration of its deoxidizing power, is shown in its action on fixed air, or carbonic acid; when heated in contact with that gas, it catches fire, and by uniting with its oxygen becomes potass, while the liberated carbon is deposited in the form of charcoal.

Upon submitting soda to the electric battery, under circumstances such as those we have already described, a bright metal was obtained, similar in its general character to potassium, but possessing distinctive peculiarities, which it is not necessary to detail; to this substance Davy gave the name of sodium.

These important discoveries were followed up by an investigation into the nature of the earths; and the results were communicated in a paper, read before the Royal Society on the 30th of June, in the same year. This investigation required still more refined and complicated processes than those which had succeeded with the fixed alkalies, owing to the in

fusable nature of the earths; the strong affinity of their bases for oxygen made it unavailing to act upon them in solution in water; and the only methods that proved successful, were those of operating upon them by electricity in some of the combinations, or of combining them at the moment of their decomposition by electricity, in metallic alloys, so as to obtain evidences of their nature and properties.

Sir Humphry Davy's Bakerian lecture of 1808, entitled, "An Account of some new Analytical Researches on the Nature of certain Bodies, particularly the Alkalies, Phosphorus, Sulphur, Carbonaceous Matter, and the Acids hitherto undecomposed; with some general Observations on Chemical Theory," abounded in elaborate experiments with the Voltaic apparatus, made with the hope of extending our knowledge of the principles of bodies, by the new powers and methods arising from the application of electricity; and announced the decomposition of boracic acid, and the development of its inflammable base at the negative surface of the battery.

The similarity of the laws of electrical and magnetical attraction had long excited the attention of the philosopher, and numerous had been the attempts to establish the existence of an identity, or intimate relation, between these two forces; but little light had been thrown upon the subject before the year 1819, when M. Oersted, secretary to the Royal Society of Copenhagen, published an account of some experiments exhibited in his lecture before the University, by which it was demonstrated that the magnetic

needle was moved from its position by the action of the galvanic apparatus. These experiments, unlike all preceding ones, were made with the two ends of the pile in communication with each other; to which circumstance are to be attributed the novel results that followed. In pursuing the investigation with a more powerful battery, M. Oersted fully ascertained that the phænomena exhibited by the needle did not depend upon electrical attraction and repulsion, for its movements were wholly at variance with such an explanation; they must depend, then, upon the production of a new energy, generated by the action of the two electricities thus brought into conflict, and which, if not identical with, must be nearly related to magnetism! moreover appeared probable, from the motions of the magnet, when differently placed with regard to the conjunctive wire, or that wire by which the opposite ends of the battery were connected, that this energy circulated, or performed a circular movement around the axis of the conductor, and thus drove the magnetic pole towards the east or west, according to the direction of the needle with reference to such a current. No sooner had this extraordinary discovery been announced in this country, than sir Humphry Davy proceeded to repeat the experiments, and with his characteristic talent, to vary and extend them. The nature and limits of this memoir will not allow us to follow

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him; it is sufficient to say, that he obtained new results, and expanded the views which Oersted had opened. He particularly investigated the magnetizing powers