Conversations on Chemistry Part 39

If you are not yet tired of experiments, I have another to show you. It consists in filling soap-bubbles with a mixture of hydrogen and oxygen gases, in the proportions that form water; and afterwards setting fire to them.

EMILY.

They will detonate, I suppose?

MRS. B.

Yes, they will. As you have seen the method of transferring the gas from the receiver into the bladder, it is not necessary to repeat it. I have therefore provided a bladder which contains a due proportion of oxygen and hydrogen gases, and we have only to blow bubbles with it.

CAROLINE.

Here is a fine large bubble rising--shall I set fire to it with the candle?

MRS. B.

If you please . . . .

CAROLINE.

Heavens, what an explosion! --It was like the report of a gun: I confess it frightened me much. I never should have imagined it could be so loud.

EMILY.

And the flash was as vivid as lightning.

MRS. B.

The combination of the two gases takes place during that instant of time that you see the flash, and hear the detonation.

EMILY.

This has a strong resemblance to thunder and lightning.

MRS. B.

These phenomena, however, are generally of an electrical nature. Yet various meteorological effects may be attributed to accidental detonations of hydrogen gas in the atmosphere; for nature abounds with hydrogen: it const.i.tutes a very considerable portion of the whole ma.s.s of water belonging to our globe, and from that source almost every other body obtains it. It enters into the composition of all animal substances, and of a great number of minerals; but it is most abundant in vegetables. From this immense variety of bodies, it is often spontaneously disengaged; its great levity makes it rise into the superior regions of the atmosphere; and when, either by an electrical spark, or any casual elevation of temperature, it takes fire, it may produce such meteors or luminous appearances as are occasionally seen in the atmosphere. Of this kind are probably those broad flashes which we often see on a summer-evening, without hearing any detonation.

EMILY.

Every flash, I suppose, must produce a quant.i.ty of water?

CAROLINE.

And this water, naturally, descends in the form of rain?

MRS. B.

That probably is often the case, though it is not a necessary consequence; for the water may be dissolved by the atmosphere, as it descends towards the lower regions, and remain there in the form of clouds.

The application of electrical attraction to chemical phenomena is likely to lead to many very interesting discoveries in meteorology; for electricity evidently acts a most important part in the atmosphere. This subject however, is, as yet, not sufficiently developed for me to venture enlarging upon it. The phenomena of the atmosphere are far from being well understood; and even with the little that is known, I am but imperfectly acquainted.

But before we take leave of hydrogen, I must not omit to mention to you a most interesting discovery of Sir H. Davy, which is connected with this subject.

CAROLINE.

You allude, I suppose, to the new miner's lamp, which has of late been so much talked of? I have long been desirous of knowing what that discovery was, and what purpose it was intended to answer.

MRS. B.

It often happens in coal-mines, that quant.i.ties of the gas, called by chemists _hydro-carbonat_, or by the miners _fire-damp_, (the same from which the gas-lights are obtained,) ooze out from fissures in the beds of coal, and fill the cavities in which the men are at work; and this gas being inflammable, the consequence is, that when the men approach those places with a lighted candle, the gas takes fire, and explosions happen which destroy the men and horses employed in that part of the colliery, sometimes in great numbers.

EMILY.

What tremendous accidents these must be! But whence does that gas originate?

MRS. B.

Being the chief product of the combustion of coal, no wonder that inflammable gas should occasionally appear in situations in which this mineral abounds, since there can be no doubt that processes of combustion are frequently taking place at a great depth under the surface of the earth; and therefore those acc.u.mulations of gas may arise either from combustions actually going on, or from former combustions, the gas having perhaps been confined there for ages.

CAROLINE.

And how does Sir H. Davy's lamp prevent those dreadful explosions?

MRS. B.

By a contrivance equally simple and ingenious; and one which does no less credit to the philosophical views from which it was deduced, than to the philanthropic motives from which the enquiry sprung. The principle of the lamp is shortly this: It was ascertained, two or three years ago, both by Mr. Tennant and by Sir Humphry himself, that the combustion of inflammable gas could not be propagated through small tubes; so that if a jet of an inflammable gaseous mixture, issuing from a bladder or any other vessel, through a small tube, be set fire to, it burns at the orifice of the tube, but the flame never penetrates into the vessel. It is upon this fact that Sir Humphry's safety-lamp is founded.

EMILY.

But why does not the flame ever penetrate through the tube into the vessel from which the gas issues, so as to explode at once the whole of the gas?

MRS. B.

Because, no doubt, the inflamed gas is so much cooled in its pa.s.sage through a small tube as to cease to burn before the combustion reaches the reservoir.

CAROLINE.

And how can this principle be applied to the construction of a lamp?

MRS. B.

Nothing easier. You need only suppose a lamp enclosed all round in gla.s.s or horn, but having a number of small open tubes at the bottom, and others at the top, to let the air in and out. Now, if such a lamp or lanthorn be carried into an atmosphere capable of exploding, an explosion or combustion of the gas will take place within the lamp; and although the vent afforded by the tubes will save the lamp from bursting, yet, from the principle just explained, the combustion will not be propagated to the external air through the tubes, so that no farther consequence will ensue.

EMILY.

And is that all the mystery of that valuable lamp?

MRS. B.