Conversations on Chemistry Part 57

MRS. B.

It is naptha, a bituminous liquid, with which I shall hereafter make you acquainted. It is almost the only fluid in which pota.s.sium can be preserved, as it contains no oxygen, and this metal has so powerful an attraction for oxygen, that it will not only absorb it from the air, but likewise from water, or any body whatever that contains it.

EMILY.

This, then, is one of the bodies that oxydates spontaneously without the application of heat?

MRS. B.

Yes; and it has this remarkable peculiarity that it attracts oxygen much more rapidly from water than from air; so that when thrown into water, however cold, it actually bursts into flame. I shall now throw a small piece, about the size of a pin's head, on this drop of water.

CAROLINE.

It instantaneously exploded, producing a little flash of light! this is, indeed, a most curious substance!

MRS. B.

By its combustion it is reconverted into potash; and as potash is now decidedly a compound body, I shall not enter into any of its properties till we have completed our review of the simple bodies; but we may here make a few observations on its basis, pota.s.sium. If this substance is left in contact with air, it rapidly returns to the state of potash, with a disengagement of heat, but without any flash of light.

EMILY.

But is it not very singular that it should burn better in water than in air?

CAROLINE.

I do not think so: for if the attraction of pota.s.sium for oxygen is so strong that it finds no more difficulty in separating it from the hydrogen in water, than in absorbing it from the air, it will no doubt be more amply and rapidly supplied by water than by air.

MRS. B.

That cannot, however, be precisely the reason, for when pota.s.sium is introduced under water, without contact of air, the combustion is not so rapid, and indeed, in that case, there is no luminous appearance; but a violent action takes place, much heat is excited, the potash is regenerated, and hydrogen gas is evolved.

Pota.s.sium is so eminently combustible, that instead of requiring, like other metals, an elevation of temperature, it will burn rapidly in contact with water, even below the freezing point. This you may witness by throwing a piece on this lump of ice.

CAROLINE.

It again exploded with flame, and has made a deep hole in the ice.

MRS. B.

This hole contains a solution of potash; for the alkali being extremely soluble, disappears in the water at the instant it is produced. Its presence, however, may be easily ascertained, alkalies having the property of changing paper, stained with turmeric, to a red colour; if you dip one end of this slip of paper into the hole in the ice you will see it change colour, and the same, if you wet it with the drop of water in which the first piece of pota.s.sium was burnt.

CAROLINE.

It has indeed changed the paper from yellow to red.

MRS. B.

This metal will burn likewise in carbonic acid gas, a gas that had always been supposed incapable of supporting combustion, as we were unacquainted with any substance that had a greater attraction for oxygen than carbon. Pota.s.sium, however, readily decomposes this gas, by absorbing its oxygen, as I shall show you. This retort is filled with carbonic acid gas. --I will put a small piece of pota.s.sium in it; but for this combustion a slight elevation of temperature is required, for which purpose I shall hold the retort over the lamp.

CAROLINE.

Now it has taken fire, and burns with violence! It has burst the retort.

MRS. B.

Here is the piece of regenerated potash; can you tell me why it is become so black?

EMILY.

No doubt it is blackened by the carbon, which, when its oxygen entered into combination with the pota.s.sium, was deposited on its surface.

MRS. B.

You are right. This metal is perfectly fluid at the temperature of one hundred degrees; at fifty degrees it is solid, but soft and malleable; at thirty-two degrees it is hard and brittle, and its fracture exhibits an appearance of confused crystallization. It is scarcely more than half as heavy as water; its specific gravity being about six when water is reckoned at ten; so that this metal is actually lighter than any known fluid, even than ether.

Pota.s.sium combines with sulphur and phosphorus, forming sulphurets and phosphurets; it likewise forms alloys with several metals, and amalgamates with mercury.

EMILY.

But can a sufficient quant.i.ty of pota.s.sium be obtained, by means of the Voltaic battery, to admit of all its properties and relations to other bodies being satisfactorily ascertained?

MRS. B.

Not easily; but I must not neglect to inform you that a method of obtaining this metal in considerable quant.i.ties has since been discovered. Two eminent French chemists, Thenard and Gay Lussac, stimulated by the triumph which Sir H. Davy had obtained, attempted to separate pota.s.sium from its combination with oxygen, by common chemical means, and without the aid of electricity. They caused red hot potash in a state of fusion to filter through iron turnings in an iron tube, heated to whiteness. Their experiment was crowned with the most complete success; more pota.s.sium was obtained by this single operation, that could have been collected in many weeks by the most diligent use of the Voltaic battery.

EMILY.

In this experiment, I suppose, the oxygen quitted its combination with the pota.s.sium to unite with the iron turnings?

MRS. B.

Exactly so; and the pota.s.sium was thus obtained in its simple state.

From that time it has become a most convenient and powerful instrument of deoxygenation in chemical experiments. This important improvement, engrafted on Sir H. Davy's previous discoveries, served but to add to his glory, since the facts which he had established, when possessed of only a few atoms of this curious substance, and the accuracy of his a.n.a.lytical statements, were all confirmed when an opportunity occurred of repeating his experiments upon this substance, which can now be obtained in unlimited quant.i.ties.

CAROLINE.

What a satisfaction Sir H. Davy must have felt, when by an effort of genius he succeeded in bringing to light and actually giving existence, to these curious bodies, which without him might perhaps have ever remained concealed from our view!

MRS. B.

The next substance which Sir H. Davy submitted to the influence of the Voltaic battery was _Soda_, the other fixed alkali, which yielded to the same powers of decomposition; from this alkali too, a metallic substance was obtained, very a.n.a.logous in its properties to that which had been discovered in potash; Sir H. Davy has called it SODIUM. It is rather heavier than pota.s.sium, though considerably lighter than water; it is not so easily fusible as pota.s.sium.

Encouraged by these extraordinary results, Sir H. Davy next performed a series of beautiful experiments on _Ammonia_, or the volatile alkali, which, from a.n.a.logy, he was led to suspect might also contain oxygen.

This he soon ascertained to be the fact, but he has not yet succeeded in obtaining the basis of ammonia in a separate state; it is from a.n.a.logy, and from the power which the volatile alkali has, in its gaseous form, to oxydate iron, and also from the amalgams which can be obtained from ammonia by various processes, that the proofs of that alkali being also a metallic oxyd are deduced.

Thus, then, the three alkalies, two of which had always been considered as simple bodies, have now lost all claim to that t.i.tle, and I have accordingly cla.s.sed the alkalies amongst the compounds, whose properties we shall treat of in a future conversation.

EMILY.