preliminary process of heating, the potassium exploded.] Sometimes we get
an awkward piece of potassium that explodes, or something like it, when it
burns. I will take another piece; and now that it is heated, I introduce
it into the jar, and you perceive that it burns in the carbonic acid not
so well as in the air, because the carbonic acid contains the oxygen
combined; but it does burn, and takes away the oxygen. If I now put this
potassium into water, I find that, besides the potash formed (which you
need not trouble about), there is a quantity of carbon produced. I have
here made the experiment in a very rough way; but I assure you that if I
were to make it carefully, devoting a day to it, instead of five minutes,
we should get all the proper amount of charcoal left in the spoon, or in
the place where the potassium was burned, so that there could be no doubt
as to the result. Here, then, is the carbon obtained from the carbonic
acid, as a common black substance; so that you have the entire proof of
the nature of carbonic acid as consisting of carbon and oxygen. And now, I
may tell you, that _whenever_ carbon burns under common circumstances, it
produces carbonic acid.
Suppose I take this piece of wood, and put it into a bottle with
lime-water. I might shake that lime-water up with wood and the atmosphere
as long as I pleased, it would still remain clear as you see it; but
suppose I burn the piece of wood in the air of that bottle. You, of
course, know I get water. Do I get carbonic acid? [The experiment was
performed.] There it is, you see that is to say, the carbonate lime,
which results from carbonic acid, and that carbonic acid must be formed
from the carbon which comes from the wood, from the candle, or any other
thing. Indeed, you have yourselves frequently tried a very pretty
experiment, by which you may see the carbon in wood. If you take a piece
of wood, and partly burn it, and then blow it out, you have carbon left.
There are things that do not shew carbon in this way. A candle does not
shew it, but it contains carbon. Here also is a jar of coal-gas, which
produces carbonic acid abundantly. You do not see the carbon, but we can
soon shew it to you. I will light it, and as long as there is any gas in
this cylinder it will go on burning. You see no carbon, but you see a
flame; and because that is bright, it will lead you to guess that there is
carbon in the flame. But I will shew it to you by another process. I have
some of the same gas in another vessel, mixed with a body that will burn
the hydrogen of the gas, but will not burn the carbon. I will light them
with a burning taper, and you perceive the hydrogen is consumed, but not
the carbon, which is left behind as a dense black smoke. I hope that by
65