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bled to collect and measure the va rious gases submitted to examina. tion. In the course of these investigations, the respirability and singularly intoxicating effects of ni. trous oxide were first discovered; which led to a new train of research concerning its preparation, compo. sition, properties, combinations, combinations, and physiological action on living beings; inquiries which were extended to the different substances connected with nitrous oxide, such as nitrous gas, nitrous acid, and ammonia; when, by multiplying experiments, and comparing the facts they disclosed, Davy ultimately succeeded in reconciling appa. rent anomalies; and, by removing the greater number of those difficulties which had obscured this branch of science, was enabled to present a clear and satisfactory his. tory of the combinations of OXYGEN and NITROGEN.

These interesting results were published in a separate volume, entitled, "Researches, Chemical and Philosophical, chiefly concerning Nitrous Oxide and its Respiration; by Humphrey Davy, Superintendant of the Medical Pneumatic Institution." Of the value of this production, the best criterion is to be found in the admiration which it excited; its author was barely twenty-one years old, and yet, although a mere boy, he was hailed as the Hercules in science, who had cleared an Augean stable of its impurities.

On obtaining the appointment of Professor at the Royal Institution, Mr. Davy gave up all his views of the medical profession, and devoted himself entirely to chemistry.

In 1802, Mr. Davy, having been elected Professor of Chemistry to the Board of Agriculture, commen.

ced a series of lectures before its members; which he continued to deliver every successive session for ten years, modifying and extending their views, from time to time, in such a manner as the progress of chemical discovery required. These discourses were published in the year 1813, at the request of the president and members of the board; and they form the only complete work on the subject of agricultural chemistry.

He has treated the interesting subject of manures with singular success; showing the manner in which they become the nourish. ment of the plant, the changes produced in them by the processes of fermentation and putrefaction, and the utility of mixing and combining them with each other. He has also pointed out the chemical princi. ples upon which depends the im provement of lands by burning and fallowing; he has elucidated the theory of convertible husbandry, founded on regular rotations of dif. ferent crops.

In the year 1803, Davy was elected a Fellow of the Royal Society; he subsequently became its secre tary, and lastly its president.

The first memoir presented to the Royal Society by Mr. Davy, was read on the 18th of June, 1801; and is entitled, "An Account of some Galvanic Combinations, formed by the Arrangement of Single Metallic Plates and Fluids, analogous to the new Galvanic Apparatus of Volta; by Mr. Humphrey Davy, Lecturer on Chemistry in the Royal Institution; communica. ted by Benjamin, Count of Rumford, V.P.R.S."

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. This grand display of sci. entific light burst upon Europe like a meteor, throwing its radiance into the darkest recesses, and open. ing to the view of the philosopher new and unexpected regions. The memoir in which these discoveries were announced constituted the Bakerian lecture; and was read before the Royal Society on the 20th November, 1806. We shall endeavour to offer as popular a re. view of its contents as the abstruse nature of the subject will allow. 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 were se. parated 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 unphi. losophical a conclusion, and show. ed that they merely arose from the decomposition of the materials employed: he found, for instance, that the glass vessel, at its point of con. tact 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 well.

washed 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 recog nising 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, embra. ced the decomposition of solid bo dies, insoluble, or difficultly soluble in water. From the effects of the electrical agency on glass, already mentioned, he very reasonably ex. pected that various earthy com. pounds night 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 contain. ing vegetable colours, without af. fecting them, or combining with them; and, secondly, that such bo. dies would even pass through che mical menstrua having stronger at tractions for them, thereby show. ing that the same power which destroyed elective affinity in the vi cinity of the metallic points, would likewise destroy or suspend its operation, throughout the whole of its circuit. Thus, proceeding step by step, with philosophic caution and unwearied perseverance, did he develope all the particular phenomena and details of his subject; his genius then took flight, and with an eagle's eye caught the plan of the whole. A new science was created; and so important and extensive were the applications of its principles in producing chemical composition and decomposition, that it justly derived the name of Electro-Chemistry. Its illustrious author, reasoning upon the phe. nomena it displayed, arrived at the plausible conclusion, that the pow. er of electrical attraction and repulsion must be identical with chemical affinity. If this be true, we at once obtain a solution of the problem, and can explain the action of the electric fluid in disuniting the elements of chemical combinations; for it is evident, that if two bodies be held together by virtue of their electrical states, by changing their electricity we shall disunite them. In this view of the subject, every substance, it is supposed, has its own inherent electricity, some be

ing positive, others negative.When, therefore, bodies in such opposite states are presented to each other, they will combine.

We proceed to consider the splendid discovery of the composition of the fixed alkalies, which was an nounced in Davy's second Bakerian Lecture, read before the Royal Society in 1807; and which was the direct result of an application of the laws of Voltaic decomposition, so admirably developed in his lecture of the preceding year.

The fixed alkalies, as well as the earths, had formerly been suspected to contain metallic bases; but as no proof, nor even experimenta! indication of the fact, could be obtained, the idea was by many entirely abandoned; and, with regard to the former of these bodies, the supposition of their being compounds of hydrogen was considered more plausible, inasmuch as they maintained a striking analogy in sensible qualities, as well as in chemical habitudes, to ammonia, whose composition had been fully established; while the supposed relations between hydrogen and oxygen, the acknowledged principle of acidity, added strength to the conjecture. Still, all the chemists in Europe had in vain attempted to effect their decomposition; they had been tortured by every variety of experiment which ingenuity could suggest or perseverance accomplish, but all in vain: nor was the pursuit abandoned, until indefatigable effort had wrecked the patience and exhausted every resource of the experimentalist.

We have already explained the important fact, established by Davy, that during the development of principles from their various combinations, by Voltaic action, an

attraction invariably subsists between oxygen and the positive pole, and inflammable matter and the negative pole; thus, in the decomposition of water, its oxygen was constantly transferred to the former, and its hydrogen to the latter. Furnished with such data, Davy proceeded to submit 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 decomposition, 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. Af Af. ter 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 connected 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. The potass began to fuse at both its points of electriza

tion; a violent effervescence commenced at the upper or positive surface, while at the lower or ne gative, instead of any liberation of electric 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 recombining with it. After various trials, Davy found that recently. distilled naphtha presented a me. dium in which it might be preserved, by covering the metal with a thin transparent film of fluid, which de. fended 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, and which may be described as follows. 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 the 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 seve.

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ral 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 splen. dour. It is also a perfect conductor of both electricity and heat. Thus far, then, it fulfils every condition of a metal; but we have now to mention a quality which has been as invariably associated with the idea of a metal as lustre; and its absence, therefore, in potassium, has given rise to a question whe. ther, after all, it can with proprie. ty be classed under this denomination; we allude to great specific gravity. Instead of possessing that ponderosity which we should have expected in a body otherwise metallic, 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 phenomenon 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!

From these observations it will be immediately perceived, that 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 elec. tric battery, under circumstances such as those we have already described, a bright metal was obtained similar in its general character to potassium, but possessing dis tinctive 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. It appears that this investigation required still more refined and complicated processes than those which had succeeded with the fixed alkalies, owing to

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