3. What was going on?

When the stir came to an end, the chalk was not there!

'Part of it has gone off in gas,' their father said. 'The rest is lime,
and it is mixed with the vinegar.'

4. 'We did not see any gas,' said Harry.

'You can't see gas. It is like air. All those bubbles were made by the
gas. It went out of the cup into the air.

'Now, get a cup of water. Come along! Where is your chalk?'

5. Father rubbed some of it into the water, and stirred it up. The water
now looked like milk.

Father poured it into the sink, and showed Harry and Dora, at the bottom
of the cup, a great many tiny grains.

6. 'Those little round things,' he said, 'are shells.'

'Shells!' said Dora, trying to see them better.

'Were live things ever in them?' asked Harry, and put a finger into the
cup to fish some out.

7. 'Yes, long, long ago. That bit of chalk had hundreds and hundreds of
shells in it. Now, mother, it is your turn! I have had mine. What do you