What is the theory, or the explanation, of this experiment?

Beautiful, and instructive, even beyond the stage already gained, but up to it as follows.

The myriads of air bubbles were those of hydrogen gas, for which sodium has no attraction or affinity; and Hydrogen, though itself inflammable, will not support the combustion of the taper or splinter of wood; but sodium has an intense attraction for the Oxygen of the water, and combined with it to form Oxide of sodium or Soda, which now remains dissolved in a portion of the undecomposed water, and being alkaline, has changed the yellow colour of the turmeric paper to brown; so that the experiment presents two results, the eduction of elementary Hydrogen by the decomposition of Water, and the production of compound Soda, by the union of elementary Oxygen and Sodium.

Let the water be now poured from the flask into a perfectly clean basin. Set this in an oven moderately heated, leaving the door open, that the whole of the water may evaporate, and then at the bottom of the basin will be found a minute portion of a white, solid, acrid, and caustic substance, that will immediately redden a moistened piece of turmeric paper most powerfully, or change a blue infusion of cabbage bright green; it is the solid and nearly anhydrous oxide of sodium or soda, exactly similar in constitution to the dull white tarnish produced when the globule of sodium was originally cut in the air, though in this case

produced by the oxygen, not of the air, but of the

water.

The Hydrogen, as it burnt from the neck of the flask, had its flame supported by the Oxygen of the surrounding air; and in so burning, actually formed the vapour of water; and if the experiment be repeated with about twice as much sodium as that already directed, all being in small pieces, sufficient hydrogen may be collected to fill more than the neck of the flask; then, by proceeding as before, and applying the smallest possible flame of a splinter of wood, to kindle the hydrogen, and instantly holding a clean, cold, and dry wine-glass over its lambent flame, the glass, instead of remaining dry, as might be reasonably anticipated, will become dim with moisture; because its cold surface condenses the hot vapour of the Water that is produced by the combination of the Hydrogen with the Oxygen of the air.

If a globule of sodium be thrown upon the surface of water contained in a large shallow plate, the evolution of hydrogen will proceed as in the flask, but it may now be directly kindled by approaching the globule with a small flame, and thus the curious phenomenon of a ball of fire floating on the water will be presented.

If a globule of sodium be thrown upon hot water, the decomposition is so intensely rapid, that the evolved hydrogen will spontaneously inflame, thus illustrating the chemical fact, that light and heat are

the usual concomitants of intense chemical combination between two or more substances.

Potassium has a greater affinity for oxygen than even sodium is found to possess; in fact, it has the most intense affinity for that element of any elementary or compound substance. It is, therefore, preserved in "naphtha,” and it is likewise the lightest solid known, its Specific Gravity being only 0.865. It might be used in the experiment with the flask, but is rather dangerous, as its action often rises beyond control, and an explosion happens. However, a globule may be thrown on a plate filled with cold water; it will float, and spontaneously inflame with a purple light, this colour being apparently due to the combustion of a portion of the vapour of the metal, in addition to that of the hydrogen of the decomposed

water.

Potassium will as rapidly decompose solid water or ice; for example, make a small hole in a lump of ice and drop into it a globule of potassium, the purple flame will instantly appear, a deep hole will be melted in the ice, and the liquid that it now contains is a strong solution of oxide of potassium or Potash, and it will act upon turmeric paper, or infusion of cabbage, like soda, because it is likewise an alkaline oxide.

Reasoning upon the extraordinary powers of the se two metals, potassium and sodium, in so energetically combining with oxygen, in whatever form it may be presented to them, the chemist is led by analogy to imagine, that volcanic eruptions, both on land and at

sea, may probably ensue from masses of these or other metals of the earths, suddenly coming into contact with oxygen or other elements, for which he knows they have intense attraction, and thus combining, displaying combustion upon a magnificent and awful scale.

If the chemist compare the measures or volumes of the definite weights of these extraordinary elements of water, he discovers them to bear the proportion of one to two, or in other words, One volume of Oxygen and Two volumes of Hydrogen, and farther ascertains, that upon exciting these to combine, they form not Three volumes, or their sum total, as might be anticipated, but only Two volumes of the Vapour of Water, or, to employ his technical expression of this extraordinary fact, the Three volumes of the Elements condense into Two of the Compound.

This fact bears analogy to that discovered by the simple experiment at page 114, where equal bulks of Water and of Alcohol contracted very considerably, or condensed by chemical union; for such it was, and no repose, no lapse of time, will cause the separation of the two liquids from each other, according to their specific gravities, as at page 341. Once chemically combined, they can only be separated by chemical agents-of which hereafter.

But, as in the case of their mutual combination, heat was evolved, so in this of the more energetic union of Oxygen and Hydrogen, the chemist discovers that heat is evolved of intensity sufficient to soften, melt, and burn, the most refractory earths, ores, and

metals; in fact, the union of Oxygen and Hydrogen affords him a degree of heat scarcely inferior to that of electricity, and a brilliant flash that rivals both it and lightning. Another extraordinary fact next presents itself; although the compound, at the instant of its formation, is in the state of Two volumes of Vapour, this, upon cooling, sustains a most excessive condensation into th part, to form liquid water!

To impress upon the mind of the young student this extraordinary fact regarding the enormous volume of gaseous elements that are included in a drop of water, let 845 peas, all similar in size, represent the One Volume of Oxygen, and 1690 similar peas represent the Two Volumes of Hydrogen; then 1690 more peas would represent the Two volumes of the Vapour of Water, which the Three Volumes form, and a Single pea will represent the drop of water that results from its condensation.

It is some little trouble to count so many peas; but once accurately done, the three heaps may be preserved in three bottles, and are extremely useful for illustrating the fact at any future time.

Knowledge of the composition of Water is of great importance in chemistry, it enables philosophers to explain many phenomena that were formerly mysterious, and affords an excellent example of a compound differing in all its habitudes from those of its elements.

Thus, gradually, have we discovered the leading characters of Carbonic acid, Water in its three physical