BIOGRAPHY OF SIR HUMPHRY DAVY, CONTINUED.

CHAPTER FOURTH.

THE author of the present memoir well remembers, in a conversation with Sir Humeinix DAVY, that the latter observed, a philosopher might always discover how posterity would appreciate his labours, from the opinion entertained of therci by contemporary foreigners ; who, being unbiassed by circumstances of personality or rivalry, will reduce every object to its just proportions and proper value. If we acknow- ledge such a standard, and submit the posthumous fame of DAVY to its measure, where is the philosopher in our times whose name will attain a higher eminence ? Let our readers recall to their recollection the bitter animosity which France and England entertained towards each other in the year 18,07, and they will form some idea of the astound- ing impression which the Bakerian Lecture must have produced on the philosophers of Paris, when,, in despite of national prejudice and national vanity, it was crowned by the Institute of France with the prize of NAPOLEON. Thus did the Voltaic Battery achieve what all the artillery of Britain could never have produced—a spontaneous and willing homage to English superiority ! But let not this, observation be considered as intended to convey the slightest degree of disrespect, or to encourage any feeling to the disparagement of the French che- mists: on the contrary, it is even a question not easily answered, to which party belongs the triumph—to him who won the laurel crown, or to those who so nobly placed it on his brow. They have set an ex- ample to future ages which may as materially advance the progress of science, as the researches which called it forth : they have shown, to adopt the language of the Edinburgh Review, that the commonwealth of Science is of no party, and of no nation ; that it is a pure republic, and always at peace. Its shades are disturbed neither by domestic malice nor foreign levy: they resound not with the cries of factions or of public animosity : Falsehood is the only enemy their inhabitants denounce, Truth, and her minister, Reason, the only leaders they follow.

The splendid discovery of the composition of the Fixed Alkalies, which we now proceed to consider, was announced in DAVY'S second Bakerian Lecture, read before the Royal Society in November 1807; and was the direct result. of an application of the laws of Voltaic de- composition, so admirably developed in his lecture of the preceding year. The memoir therefore aftbrds a very happy instance of philo- sophical induction, the most brilliant results having been obtained through a chain of reasoning and experiment ; and, with the exception perhaps of NEWTON'S account of his first discoveries in • Optics, the annals of Science cannot boast of such another monument of tran- scendent genius. Had it been true, as was at the time insinuated with singular inconsistency, and we will add with equal unfairness, by the Edinburgh Reviewers, that the decomposition of the alkalies was accidentally effected by the high power of the apparatus placed at his disposal, DAVY'S claims to our admiration would have assumed a very different character : in such a case he might be said to have forced open the temple by direct violence, instead of having discovered and touched the secret spring by which its portals were unclosed.

The Fixed Alkalies, as well as the Earths, had formerly been sus- pected to contain metallic bases ; but as no proof, nor even experi- mental 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 re- lations 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. Such was the forlorn and disheartening position of the philosopher, when DAVY proffered his assistance. He created new instruments, new powers, and fresh resources ; and, interrogating Nature on a different plan, her long-cherished secret was revealed.

We have already explained the important fact, established by DAVY, that during the development of principles, from their various com- binations, 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. first attempts were made on solutions of the al- kalies ; 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 decom- position, Potass, in a state of igneous fusion, was submitted to ex- periment : 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 in- sulated disc of platina, and connected with the negative side of the battery in a state of intense activity, and a platina wire commu- nicating with the positive side, was at the same instant brought into contact with the upper surface of the alkali. What followed ?—A series of ph=omena, each of which the reader will understand as it is announced ; for it will be in strict accordance with those laws which DAVY had previously discovered, and which we have been labouring, to render intelligible. The potass began to fuse at both its points of electfization; a violent effervescence commenced at the upper or positive surface, while at the lower or negative, instead of any libera- tion 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. What must have been the sensations of DAVY at this moment ! He had decomposed the alkali, and

discovered it to contain a metallic basis. The gaseous matter deve- loped 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 at-

traction for oxygen, that it speedily reverted to the state of alkali by recombining with it. After various trials, DAVI, 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 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 tempera- ture of 70° Fahrenheit, it exists in small globules, which possess the metallic lustre, opacity, and general appearance of mercury ; so that i

when a globule of mercury s 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. 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 whether,, after all, it can with propriety be classed under this denomination ;—we allude to great specific gravity. Instead of pos- sessing that ponderosity which we -should have expected in a body otherwise metallic, it is so light as not only to swim upon the surface of water, but upon that of naphtha, by far the lightest fluid in nature. We may here introduce an anecdote, which will serve to show, that so inseparable, by long association, are the ideas of ponderosity and metallic splendour, that the evidence even of our senses may fail to dis- unite them. Shortly after DAVY had succeeded in obtaining a quantity of his newly-discoveredbody, Dr. GEORGE PEARSON happened to enter the laboratory, and having been shown the substance, and interrogated as to its nature, he at once exclaimed, upon seeing its lustre, " Why, it is metallic, to be sure ; " and then, balancing it upon his finger, lie added, " and, bless me, how heavy it is ! " Thrown upon water, it in- stantly 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 phainomenon 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 na- ture 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 .observatiens the reader will immediately perceive, that the decomposition of the fixed alkali placed in the hands of the experi- mentalist 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.

As this account has extended beyond the limits we originally designed for it, we shall merely add, that, 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 topotassium, but possessing distinctive peculiarities which it is not ne- cessary to detail : to this substance'DAvv 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 the infusible nature of the earths: the strong affinity of their bases for oxygen made it unavailing to act upon them in solu- tion in water ; and the only methods that proved successful, were those of operating upon them by electricity in seine of the combinations, or of combining them at the moment of their decomposition by electri- city, in metallic alloys, so as to obtain evidences of their nature and properties. Our readers, we are quite sure, would not thank us were we to follow the philosopher through all the intricate paths of this in- vestigation: suffice it to say, that, although lie was unable to produce the metallic bases of the earths in the same unequivocal form as he produced those of the alkalies, he furnished sufficient evidence of their being metallic oxides.

What an immense step, then, has been made in the investigation of Nature ! In sciences kindred to chemistry, the knowledge of the composition of these bodies, and the 'analogies arising from it, have opened new views, and led to the soliition of many problems. In Geology, for instance, has it not shown that agents may have operated in the formation of rocks and earths, 'which have not hitherto been supposed to exist ? It is evident that the metals of the earths can- not exist'at tfie surface of our -globe, but it is very probable that they, May constitute a part of its interior; and such an assumption would at once offer a plausible theory for the plizennmena of volcanoes, the formation of lavas, and the excitement and effects of subterraneous heat, and might even lead to a general hypothesis in geology. Our readers must, for the present, be satisfied with these loose hints : we• shall hereafter show, that our illustrious chemist followed them up by numerous observations and experiments in & volcanic country. We remember with delight the beautiful display of his theory, as exhibited in an artificial volcano on the table of the Royal Institution :—a mountain was modelled in clay, and a quantity of the metallic bases" introduced into its interior ; on water being poured Upon it, the metals were soon thrown into violent action—successive explosions were pro- duced—boiling lava was seen flowing down its sides from a crater in miniature—mimic lightnings played around ; and the, tumultuous ap- plause of the audience might almost, in the instant of dramatic illusion, have been mistaken for the shouts of the alarmedfugitives of Hercula- neum or Pompeii.