Conversations on Chemistry Part 44

The _phosph.o.r.etted hydrogen gas_ has this remarkable peculiarity, that it takes fire spontaneously in the atmosphere, at any temperature. It is thus, probably, that are produced those transient flames, or flashes of light, called by the vulgar _Will-of-the Whisp_, or more properly _Ignes-fatui_, which are often seen in church-yards, and places where the putrefactions of animal matter exhale phosphorus and hydrogen gas.

CAROLINE.

Country people, who are so much frightened by those appearances, would soon be reconciled to them, if they knew from what a simple cause they proceed.

MRS. B.

There are other combinations of phosphorus that have also very singular properties, particularly that which results from its union with lime.

EMILY.

Is there any name to distinguish the combination of two substances, like phosphorus and lime, neither of which are oxygen, and which cannot therefore produce either an oxyd or an acid?

MRS. B.

The names of such combinations are composed from those of their ingredients, merely by a slight change in their termination. Thus the combination of sulphur with lime is called a _sulphuret_, and that of phosphorus, a _phosphuret of lime_. This latter compound, I was going to say, has the singular property of decomposing water, merely by being thrown into it. It effects this by absorbing the oxygen of water, in consequence of which bubbles of hydrogen gas ascend, holding in solution a small quant.i.ty of phosphorus.

EMILY.

These bubbles then are _phosph.o.r.etted hydrogen gas_?

MRS. B.

Yes; and they produce the singular appearance of a flash of fire issuing from water, as the bubbles kindle and detonate on the surface of the water, at the instant that they come in contact with the atmosphere.

CAROLINE.

Is not this effect nearly similar to that produced by the combination of phosphorus and sulphur, or, more properly speaking, the _phosphuret of sulphur_?

MRS. B.

Yes; but the phenomenon appears more extraordinary in this case, from the presence of water, and from the gaseous form of the combustible compound. Besides, the experiment surprises by its great simplicity. You only throw a piece of phosph.o.r.et of lime into a gla.s.s of water, and bubbles of fire will immediately issue from it.

CAROLINE.

Cannot we try the experiment?

MRS. B.

Very easily: but we must do it in the open air; for the smell of the phosphorated hydrogen gas is so extremely fetid, that it would be intolerable in the house. But before we leave the room, we may produce, by another process, some bubbles of the same gas, which are much less offensive.

There is in this little gla.s.s retort a solution of potash in water; I add to it a small piece of phosphorus. We must now heat the retort over the lamp, after having engaged its neck under water--you see it begins to boil; in a few minutes bubbles will appear, which take fire and detonate as they issue from the water.

CAROLINE.

There is one--and another. How curious it is! --But I do not understand how this is produced.

MRS. B.

It is the consequence of a display of affinities too complicated, I fear, to be made perfectly intelligible to you at present.

In a few words, the reciprocal action of the potash, phosphorus, caloric, and water are such, that some of the water is decomposed, and the hydrogen gas thereby formed carries off some minute particles of phosphorus, with which it forms phosph.o.r.etted hydrogen gas, a compound which spontaneously takes fire at almost any temperature.

EMILY.

What is that circular ring of smoke which slowly rises from each bubble after its detonation?

MRS. B.

It consists of water and phosphoric acid in vapour, which are produced by the combustion of hydrogen and phosphorus.

CONVERSATION IX.

ON CARBON.

CAROLINE.

To-day, Mrs. B., I believe we are to learn the nature and properties of CARBON. This substance is quite new to me; I never heard it mentioned before.

MRS. B.

Not so new as you imagine; for carbon is nothing more than charcoal in a state of purity, that is to say, unmixed with any foreign ingredients.

CAROLINE.

But charcoal is made by art, Mrs. B., and a body consisting of one simple substance cannot be fabricated?

MRS. B.

You again confound the idea, of making a simple body, with that of separating it from a compound. The chemical processes by which a simple body is obtained in a state of purity, consist in _unmaking_ the compound in which it is contained, in order to separate from it the simple substance in question. The method by which charcoal is usually obtained, is, indeed, commonly called _making_ it; but, upon examination, you will find this process to consist simply in separating it from other substances with which it is found combined in nature.

Carbon forms a considerable part of the solid matter of all organised bodies; but it is most abundant in the vegetable creation, and it is chiefly obtained from wood. When the oil and water (which are other const.i.tuents of vegetable matter) are evaporated, the black, porous, brittle substance that remains, is charcoal.

CAROLINE.

But if heat be applied to the wood in order to evaporate the oil and water, will not the temperature of the charcoal be raised so as to make it burn; and if it combines with oxygen, can we any longer call it pure?

MRS. B.

I was going to say, that, in this operation, the air must be excluded.

CAROLINE.

How then can the vapour of the oil and water fly off?