Conversations on Chemistry Part 34

CAROLINE.

You love to deal in paradoxes to-day, Mrs. B. --Fire, then, produces water?

MRS. B.

The combustion of hydrogen gas certainly does; but you do not seem to have remembered the theory of combustion so well as you thought you would. Can you tell me what happens in the combustion of hydrogen gas?

CAROLINE.

The hydrogen combines with the oxygen, and their opposite electricities are disengaged in the form of caloric. --Yes, I think I understand it now--by the loss of this caloric, the gases are condensed into a liquid.

EMILY.

Water, then, I suppose, when it evaporates and incorporates with the atmosphere, is decomposed and converted into hydrogen and oxygen gases?

MRS. B.

No, my dear--there you are quite mistaken: the decomposition of water is totally different from its evaporation; for in the latter case (as you should recollect) water is only in a state of very minute division; and is merely suspended in the atmosphere, without any chemical combination, and without any separation of its const.i.tuent parts. As long as these remain combined, they form WATER, whether in a state of liquidity, or in that of an elastic fluid, as vapour, or under the solid form of ice.

In our experiments on latent heat, you may recollect that we caused water successively to pa.s.s through these three forms, merely by an increase or diminution of caloric, without employing any power of attraction, or effecting any decomposition.

CAROLINE.

But are there no means of decomposing water?

MRS. B.

Yes, several: charcoal, and metals, when heated red hot, will attract the oxygen from water, in the same manner as they will from the atmosphere.

CAROLINE.

Hydrogen, I see, is like nitrogen, a poor dependant friend of oxygen, which is continually forsaken for greater favourites.

MRS. B.

The connection, or friendship, as you choose to call it, is much more intimate between oxygen and hydrogen, in the state of water, than between oxygen and nitrogen, in the atmosphere; for, in the first case, there is a chemical union and condensation of the two substances; in the latter, they are simply mixed together in their gaseous state. You will find, however, that, in some cases, nitrogen is quite as intimately connected with oxygen, as hydrogen is. --But this is foreign to our present subject.

EMILY.

Water, then, is an oxyd, though the atmospherical air is not?

MRS. B.

It is not commonly called an oxyd, though, according to our definition, it may, no doubt, be referred to that cla.s.s of bodies.

CAROLINE.

I should like extremely to see water decomposed.

MRS. B.

I can gratify your curiosity by a much more easy process than the oxydation of charcoal or metals: the decomposition of water by these latter means takes up a great deal of time, and is attended with much trouble; for it is necessary that the charcoal or metal should be made red hot in a furnace, that the water should pa.s.s over them in a state of vapour, that the gas formed should be collected over the water-bath, &c.

In short, it is a very complicated affair. But the same effect may be produced with the greatest facility, by the action of the Voltaic battery, which this will give me an opportunity of exhibiting.

CAROLINE.

I am very glad of that, for I longed to see the power of this apparatus in decomposing bodies.

MRS. B.

For this purpose I fill this piece of gla.s.s-tube (PLATE VIII. fig. 1.) with water, and cork it up at both ends; through one of the corks I introduce that wire of the battery which conveys the positive electricity; and the wire which conveys the negative electricity is made to pa.s.s through the other cork, so that the two wires approach each other sufficiently near to give out their respective electricities.

[Ill.u.s.tration: Plate VIII. Vol. I. p. 206

Fig. 1. Apparatus for the decomposition of water by the Voltaic Battery.

Fig. 2. Apparatus for decomposing water by Voltaic Electricity & obtaining the ga.s.ses separate.

Fig. 3. Apparatus for preparing & collecting hydrogen gas.

Fig. 4. Receiver full of hydrogen gas inverted over water.

Fig. 5 Slow combustion of hydrogen gas.

Fig. 6. Apparatus for ill.u.s.trating the formation of water by the combustion of hydrogen gas.

Fig. 7. Apparatus for producing harmonic sounds by the combustion of hydrogen gas.]

CAROLINE.

It does not appear to me that you approach the wires so near as you did when you made the battery act by itself.

MRS. B.

Water being a better conductor of electricity than air, the two wires will act on each other at a greater distance in the former than in the latter.

EMILY.

Now the electrical effect appears: I see small bubbles of air emitted from each wire.

MRS. B.

Each wire decomposes the water, the positive by combining with its oxygen which is negative, the negative by combining with its hydrogen which is positive.

CAROLINE.

That is wonderfully curious! But what are the small bubbles of air?

MRS. B.