of platinum, or some other form of that metal, gradually converted the whole of the alcohol into acetic acid.

The lamp in this form has been used for a nightlamp: it gives light enough to see the time by a watch held close to it; and if more light be required, a piece of amadou may be carefully inflamed at it, and then a light procured in the usual way. Mr. Batka proposes to use Eau de Cologne in place of common spirit of wine, and finds, that then the fragrance diffused is very grateful; being, in fact, occasioned by the actual formation of aromatic vinegar, during the whole time the lamp burns.

COMBUSTION.

Why are certain bodies combustible?

Because of an intense chemical action which takes place in them, and is connected with their electrical energies; “for, all bodies which powerfully act upon each other, are in the opposite electrical states of positive and negative; and the disengagement of heat and light, (which characterizes combustion) may depend upon the annihilation of those opposite states which happens whenever they combine.' -Brande.

Sir H. Davy has asserted, "that in any case combustion is merely the appearance produced, when substances, which have perhaps still stronger attraction for each other than quick-lime and water, are combining chemically, so as to become heated, at least, to the degree of incandescence. During the phenomenon, there is not, as was formerly supposed, something altogether consumed and destroyed, or something called plogiston escaping; the substances concerned are but assuming a new form and arrangement.

Of the substances called combustible, there are only a few which will begin to unite or burn at the common temperature of our globe, the others requiring to be at some higher and peculiar temperature. Thus, phos

phorus begins to burn at 150°, sulphur at 550°, charcoal at 750°, hydrogen at 800°; it appearing, that up to these temperatures, the attraction of the atoms among themselves is sufficient to resist the other attraction, or that of oxygen. But when the combustion once begins, the temperature, from the effect of the combustion itself, rises instantly, much beyond the degree necessary for the commencement of the process. Oxygen and hydrogen, which begin to burn or combine at 800°, produce a flame of as intense heat as human art can excite.-Arnott.

Why are other bodies, as a stone, or brick, termed incombustible?

Because, when heated, they undergo no change except an augmentation of temperature, and when left to themselves, they soon cool again, and become as at first. But, with combustible bodies, the case is very different. When heated to a certain degree in the open air, they suddenly become much hotter of themselves, and continue for a considerable time intensely hot, sending out a copious stream of coloric and light to the surrounding bodies. This emission, after a certain period, begins to diminish, and at last ceases altogether. The combustible body has now undergone a complete change,-it is converted into a substance possessing very different properties, and no longer capable of combustion.-Thomson.

Again, of substances burning in air, those which are originally aëriform, as coal gas, or which, on being heated are vapourised or rendered aëriform, before their union with the oxygen of the atmosphere takes place, as oil or wax, assume the appearance of flame; viz. the aëriform particles usually invisible, are raised to the incandescent temperature; but when the substance combining with the oxygen remains solid, while its particles are gradually lifted away by the oxygen acting only at the surface of their mass, it appears during the whole time only as a red-hot stone.

PART V.

The latter is the case of charcoal, coke, Welch stone, coal, &c. while in the case of wood, common coal, &c. a greater or less portion of the inflammable matter, is, by the heat of the combustion, converted into vapour, and produces the beautiful appearance of flame.

Men, now grown familiar with prodigies, have almost ceased to be moved by them; but few persons can resist a feeling of wonder and admiration when chemistry, in its progress of discovery, every now and then calls forth the hidden spirit of combustion in some new or less familiar guise; for instance, when a piece of iron wire, lighted as a taper in oxygen gas, burns with such resplendent brilliancy; or, when phosphorus, similarly placed, throws around its overpowering flood of flame; or, when small portions of the metal called potassium, being cast upon the surface of water, become as beads of most intense light, running about there, and crossing as in a merry dance; -or, lastly, when flames produced from particular substances are seen rising deep-tinged with most vivid and beautiful colours.-Arnott.

Why does a common fire smoke?

Because of the vapour of the water from the moisture of the fuel; and the carburetted hydrogen and bituminous substances, formed during combustion by the union of the hydrogen of the combustible with the oxygen of the atmosphere.

Why does a draught support a fire?

Because it flows towards the fire-place, to occupy the vacancy left by the air that has undergone decomposition, and which, in its turn, becomes decomposed also. Hence, a supply of caloric is furnished without intermission, till the whole of the combustible is saturated with oxygen.-Parkes.

Why do not coals, wood, &c. being combustibles, take fire on exposure to the air?

Because all such bodies require to have a certain preparatory temperature before beginning to combine with the oxygen of the atmosphere.

Why is heat produced by combustion?

Because of the decomposition of the oxygen gas of the atmosphere; for, as the oxygen combines with the combustible body, it disengages the caloric which is held when in the state of a gaseous substance. Or, to speak with more precision, the act of combustion effects a real analysis of atmospheric air; for while the oxygen combines with the combustible, the caloric, in the form of sensible heat, is thrown off in every direction.-Parkes.

Why do lamps with many wicks, placed near each other, give much more light than the same number of wicks would, if placed in separate lamps ?

Because the light given out by a combustible body is in proportion to the elevation of temperature; and in this case the many wicks communicate heat to each other.

Why is oxygen a powerful supporter of combustion?

Because it is more abundantly diffused throughout nature than any of the other elementary bodies; it forms eight-ninths of the weight of water, about onefifth of the weight of the atmosphere, and a relative proportion of the earthy and mineral bodies which form the solid matter of the globe. Hence, it is present everywhere, and ready to unite itself with any matter exposed to it at the necessary temperature. Why is oxygen gas called vital air?

Because it is a powerful supporter of respiration. Thus, a small animal confined in oxygen gas, lives thrice as long as when confined in the same bulk of common air; but we are not thence to conclude that it is fit for the support of life; on the contrary, an animal made to breathe oxygen for any length of time, falls a sacrifice to excess of arterial action; and after death, the blood in the veins is found as florid as that in the arteries.-Brande.

Why is it considered that oxygen unites with the combustible body in the act of burning?

Because, if a substance be burnt in a sufficient quantity of oxygen gas, in a close vessel, and the product preserved, the whole will be found to be increased in weight exactly in proportion to the oxygen gas consumed, and the combustible body will then have become incombustible.-Parkes.

Fourcroy observes, "this view of combustion authorises us to divide almost all the productions of nature into two grand classes; one of combustible bodies, the other of bodies already burnt; in the masses and action of the former we discern the causes of inflammable meteors, the perpetual alteration of the surface of the earth, volcanoes, &c. In the existence of the latter we perceive the source of the number and diversity of acids, saline compounds, oxides, and metallic salts, which vary in a thousand ways the appearance of ores, &c."

Why is not a goblet, when pushed into water with the mouth downwards, filled with water?

Because the air in the goblet resists the entrance of the water; and, if the goblet be inverted over a floating lighted taper, this will continue to float under it, and to burn in the contained air, however deep in the water it be carried, exhibiting the curious phenomenon of a light below water, and itself an emblem of the living inmate of a diving bell, which is merely. a larger goblet, with a man instead of a candle. Arnott.

Why is the name fuel given only to the substances which combine with oxygen, and not to the oxygen itself?

Because, probably, the former being solid or liquid, and therefore more obvious to sense, were known as producers of combustion long before the existence of the aëriform ingredient was even suspected.—Arnott.