Now he can take a bit of chalk to pieces, so that it shall become several different things, none of which is chalk, or like chalk at all.  And then his brother Synthesis can put them together again, so that they shall become chalk, as they were before.  He can do that very nearly, but not quite.  There is, in every average piece of chalk, something which he cannot make into chalk again when he has once unmade it.

What that is I will show you presently; and a wonderful tale hangs thereby.  But first we will let Analysis tell us what chalk is made of, as far as he knows.

He will say—­Chalk is carbonate of lime.

But what is carbonate of lime made of?

Lime and carbonic acid.

And what is lime?

The oxide of a certain metal, called calcium.

What do you mean?

That quicklime is a certain metal mixed with oxygen gas; and slacked lime is the same, mixed with water.

So lime is a metal.  What is a metal?  Nobody knows.

And what is oxygen gas?  Nobody knows.

Well, Analysis, stops short very soon.  He does not seem to know much about the matter.

Nay, nay, you are wrong there.  It is just “about the matter” that he does know, and knows a great deal, and very accurately; what he does not know is the matter itself.  He will tell you wonderful things about oxygen gas—­how the air is full of it, the water full of it, every living thing full of it; how it changes hard bright steel into soft, foul rust; how a candle cannot burn without it, or you live without it.  But what it is he knows not.

Will he ever know?

That is Lady Why’s concern, and not ours.  Meanwhile he has a right to find out if he can.  But what do you want to ask him next?

What?  Oh!  What carbonic acid is.  He can tell you that.  Carbon and oxygen gas.

But what is carbon?

Nobody knows.

Why, here is this stupid Analysis at fault again.

Nay, nay, again.  Be patient with him.  If he cannot tell you what carbon is, he can tell you what is carbon, which is well worth knowing.  He will tell you, for instance, that every time you breathe or speak, what comes out of your mouth is carbonic acid; and that, if your breath comes on a bit of slacked lime, it will begin to turn it back into the chalk from which it was made; and that, if your breath comes on the leaves of a growing plant, that leaf will take the carbon out of it, and turn it into wood.  And surely that is worth knowing,—­that you may be helping to make chalk, or to make wood, every time you breathe.

Well; that is very curious.

But now, ask him, What is carbon?  And he will tell you, that many things are carbon.  A diamond is carbon; and so is blacklead; and so is charcoal and coke, and coal in part, and wood in part.

What?  Does Analysis say that a diamond and charcoal are the same thing?