With the help of a diagram, explain the process of destructive distillation of wood.

Let us take two glass tubes. In one tube we put some small pieces of soft wood and in other tube, we put some water. These two tubes are then arranged as shown in the figure. When we heat the tube with a burner, we can find that a gas goes out through the open end of the delivery tube. If we a light a match stick near this gas, it starts burning showing that it is a combustile gas. This combustile gas obtained from wood is called wood gas and it is used as a fuel. In another tube we can find that there are drops of deep black liquid at the bottom of the tube, under water. This deep black liquid is called tar. The black residue left behind the other tube is called charcoal. When this tube is cooled we can remove the charcoal from it.