The apparatus:
Mercury(II)oxide (HgO) is an orange solid .
A small quantity is in the test tube.
On the left side, we see a gas trap.
The test tube is heated.
The reaction starts.
A colorless gas is collected in the gas trap.
In the test tube we see shining metallic drops: It is elementary mercury (Hg).
We lighten a pece of wood.
The wood is still incandescent.
In contact with the trapped gas it starts to burn again.
The colorless gas is the elementary substance oxygen.
