A Bunsen burner is made up of the base, a barrel with air holes, a collar, a needle valve and a gas hose. Some of these parts can be adjusted to change the properties of the flame that the burner produces.
The gas hose is a rubber tube that connects the needle valve inside the base of the Bunsen burner to the gas supply. It is corrugated and taped at the end to prevent gas leaks during use.
The needle valve, sometimes known as the gas flow valve, is used to change the flow of gas, and is used to alter the size of the flame. The more open the valve is, the taller the flame at the top of the barrel. It is this part that allows the gas to flow into the barrel.
The barrel is a metal tube screwed onto the base over the valve. It has holes on it which allow air to come into the barrel. The mixture of gas and air is what is ignited at the top of the barrel.
The collar is an adjustable piece of metal that can be turned or screwed to open and close the holes on the barrel. When opened, the collar allows more air into the barrel, producing a hotter flame at the top.